CHAPTER -3

Synthesis &

Characterizations of

Metal Complexes

Synthesis & Characterizations of Metal Complexes

63

3.1 INTRODUCTION

Transition metal complexes represent an important class of compounds because of

their applications in wide range areas from material sciences to biological sciences.

Metal complexes are being employed as diagnostic agents and have opened

moderately new area of medicinal research and have thrived rapidly from last 4-5

decades [1].

Metal complexation is of widespread interest. It is studied not only by inorganic

chemists, but by physical and organic chemists and by biochemists, pharmacologists,

molecular biologists and environmentalists.

The metal complexes in pharmaceuticals have gained access over traditional organic

dominated drugs, due to their potential use as regulators of gene expression and tools

of molecular biology [2]. The metal ions are also known to accelerate drug action [3]

and the efficiency of a therapeutic agent can often be enhanced by coordination with a

metal ion (Goldstein et al., 1986). Many complexes, including the platinum group,

have been synthesized and tested in a number of biological systems after the

discovery of the inorganic anti-cancer agent, cisplatin (Figure-3.1).

Figure-3.1: Cisplatin

Coordination Compounds are the backbone of modern inorganic and bio–inorganic

chemistry and chemical industry. Coordination compounds are important due to their

role in biological and chemical systems in various ways. It has been observed that

metal complexes with appropriate ligands are chemically more significant and

specific than the metal ions and original [4,5].

P t

C l N H 3

C l N H 3

C i s p l a t i n

Synthesis & Characterizations of Metal Complexes

64

The therapeutic and diagnostic properties of transition metal complexes have

fascinated extensive attention leading to their application in many areas of

contemporary medicine [6]. Coordination complexes are gaining increasing

importance in recent years particularly in the design of repository; slow release or

long acting drugs in nutrition and in the study of metabolism [3]. Many coordination

compounds of transition metal ions also accomplish nucleolytic cleavage [7].

Apart from these, there has been a growing interest in the role of metal ions and their

complexes in biological systems [8,9]. Metal complexes have been explored for their

catalytic and biological activities [10]. Many enzymes and proteins involving multi-

metal systems have been reported [11,12]. Coordination chemistry has now leaped

into many areas of science such as analytical chemistry, medicinal chemistry,

metallurgy, industrial chemistry, material science etc.

Complexes are structure containing a metal ion bonded to a group of surrounding

molecule or ions (ligand). Complexes may be non-ionic (neutral) or cationic or

anionic, depending on the charges carried by the central metal ion and the coordinated

groups.

All metals form complexes, although the extent of formation and nature of these

depend very largely on the electronic structure of the metal. A metal ion in solution

does not exist in isolation, but in combination with ligands (such as solvent molecules

or simple ions) or chelating groups, giving rise to complex ions or coordination

compounds.

These complexes contain a central atom or ion, often a transition metal, and a cluster

of ions or neutral molecules surrounding it. Many complexes are relatively unreactive

species remaining unchanged throughout a sequence of chemical or physical

operations and can often be isolated as stable solids or liquid compounds.

Other complexes have a much more transient existence and may exist only in solution

or be highly reactive and easily converted to other species.

Synthesis & Characterizations of Metal Complexes

65

Biologically relevant metal complexes have several requirements in terms of their

synthetic design. First, a biologically active metal complex should have a sufficiently

high thermodynamic stability to deliver the metal to the active site. The metal-ligand

binding should be hydrolytically stable. The kinetics with which the metal ion

undergoes ligation or de-ligation reactions is of great importance. The molecular

weight of the metal complex is also critical. The compounds of low molecular weight

with neutral charge and some water solubility are soluble in almost any medium and

may slip through biological membranes by passive diffusion. Generally, drug

combinations have proven to be an essential feature of antimicrobial treatment due to

a number of important considerations: (i) they increase activity through the use of

compounds with synergistic or additive activity; (ii) they thwart drug resistance; (iii)

they decrease required doses, reducing both cost and the chances of toxic side effects;

(iv) they increase the spectrum of activity.

3.1.1 TERMS USED IN COORDINATION CHEMISTRY

Coordination number

In a complex the number of ligand donor atoms to which the metal is directly bonded

is defined as the coordination number (CN) of a metal ion and this can vary from 2 to

greater than 12. For example, in the complex ions, [PtCl6]2–

and [Ni(NH3)2]+2

, the

coordination number of Pt and Ni are 6 and 4 respectively.

Ligand

A ligand is an ion or molecule that binds to a central metal atom to form

a complex (alternatively known as a coordination entity). The term ligand (ligare

[Latin], to bind) was first used by Alfred Stock in 1916 in relation to silicon

chemistry. The first use of the term was by H. Irving and R.J.P. Williams [13] in a

British journal in their paper describing what is now called the Irving-Williams series.

A ligand is a neutral molecule or ion having a lone pair that can be used to form a

bond to a metal ion that is in turn known as complexing agents. The formation of a

metal-ligand bond therefore can be described as the interaction between Lewis base

(the ligand) and a Lewis acid (the metal ion). The bond between metal ion and ligand

as a result of their sharing electrons is known as dative covalent bond (Brown et al.,

2006) or co-ordinate covalent bond. The transition metals have tendency to form co-

ordination compounds with Lewis bases with groups which are able to donate an

Synthesis & Characterizations of Metal Complexes

66

electron pair. The ligand provides both of the electrons for the bond that forms

between itself and the central metal or ion. The overall charge on a complex is the

arithmetic sum of the oxidation state of the metal in the center plus the charge(s)

brought to the complex by each ligand.

Ligands can be further characterised as monodentate, bidentate, tridentate etc.

according to number of electron donor atom present in it.

Ambidentate ligands are monodentate ligands that can bind in two possible places.

For example, the thiocyanate ion, SCN- can bind to the central metal atom/ion at

either the sulfur or the nitrogen. The nitrate ion NO2- can bind to central metal at

either the nitrogen atom or one of the oxygen atoms.

The atom within a ligand that can donate a pair of electron to the central atom or ion

and bonded to it is called the donor atom. The atom that accepts this lone pair of

electron is known as acceptor. The co-ordinate bond is always shown by an arrow

(→) pointing from donor to acceptor.

Chelate Compound or Chelate

The term chelate was first applied in 1920 [14], which stated:

"The adjective chelate, derived from the great claw or chela (chely- Greek) of the

lobster or other crustaceans, is suggested for the caliperlike groups which function as

two associating units and fasten to the central atom so as to produce heterocyclic

rings."

Complexes involving simple ligands, i.e., those forming only one bond are described

as co-ordination compound. A complex of a metal ion with 2 or more groups on a

multidentate ligand is called a chelate or a chelate compound. There is no

fundamental difference between co-ordination compound and a chelate compound

except that in a chelate compound, ring influence the stability of compound. Thus, a

chelate can be described as a heterocyclic ring structure in which a metal atom is a

member of ring. The stability of a chelate is usually much greater than that of

corresponding unidentate metal complex.

Synthesis & Characterizations of Metal Complexes

67

Chelating agent

Ligands having more than one electron donating groups are called chelating agents.

The most effective complexing agent in ligands are amino and carboxylate ions. All

the multidentate ligands important in analytical chemistry contain the structure

component. Morgan and his colleagues made the first truly systematic studies of this

class of compound, but they were mainly interested in the -diketones. From that time

to the present day new analytical reagents have been developed, but, in addition,

many contributions to structural and synthetic chemistry have been made. The more

important early organic reagents and the dates of their introduction in analysis are

listed in Table:3.1.

Table-3.1: Important early organic reagents and the dates of their introduction in

analysis

*It is emphasized that the dates refer to the first application in chemical analysis, even

though the compound may have been known or its reactions noted earlier. Salicyclic

acid provides some difficulties; according to Welcher4 the reaction with iron was

noted by Vogel in 1876: several later investigators commented on it before the turn of

the century, but it was first used for analysis by Gregory (Welcher, loc cit); hence this

is the reference quoted above. Yet Pulsifer (1904) (supra) used the reaction to

compare it with acetylacetone, but gives no reference to earlier work; he may have

been the first to use it. Only an extensive examination of the original papers could

establish the exact situation. It might well turn out that salicylic acid was the first

synthetic organic reagent to be used in chemical analysis.

Reagent Year Author Application

1-Nitroso-2-naphthol 1885 Jlinski and von Knorre Co

1,5-Diphenylcarbohydrazide 1900 Cazeneuve Several metals

Acetylacetone 1904 Pulsifer Fe

Dimethylglyoxime 1905 Tschugaeff Ni

Salicyclic acid* 1907 Gregory Fe

Cupferron 1909 Baudisch Several metals

Alizarin 1915 Atack Al

α-Benzoin-oxime 1923 Feigl Cu

Dithizone 1925 Fischer Several metals

8-Quinolinol 1926 Berg and Hahn (independently) Several metals

Rhodizonic acid 1926 Feigl Several metals

p-Dimethylaminobenzalrhodanine 1928 Feigl Ag

2,2'-Dipyridyl 1930 Hill Fe

Tris(phenanthroline)FeII

1931 Walden, Hammett and Chapman Redox indicator

Synthesis & Characterizations of Metal Complexes

68

3.1.2 History

Werner’s theory

The concept of a metal complex originated in the work of Alfred Werner. He prepared

and characterized a large number of coordination compounds and studied their

physical and chemical behavior by simple experimental techniques. He proposed the

concept of a primary valence & a secondary valence for a metal ion and in 1898

propounded his theory of coordination compounds. His theory allows one to

understand the difference between coordinated and ionic in a compound. Werner was

awarded the first Nobel Prize in Inorganic chemistry in 1913 for his work on the

linkage of atoms and the coordination

theory. The main postulates are:

1. In coordination compounds metals show two types of linkages (valences)-

primary and secondary.

2. The primary valences are normally ionisable and are satisfied by negative

ions.

3. The secondary valences are non ionisable. These are satisfied by neutral

molecules or negative ions. The secondary valence is equal to the

coordination number and is fixed for a metal.

4. The ions/groups bound by the secondary linkages to the metal have

characteristic spatial arrangements corresponding to different coordination

numbers.

In modern formulations, such spatial arrangements are called coordination polyhedra.

The species within the square bracket are coordination entities or complexes and the

ions outside the square bracket are called counter ions.

He further postulated that octahedral, tetrahedral and square planar geometrical

shapes are more common in coordination compounds of transition metals. In 1914,

Werner resolved the first coordination complex, called hexol (Figure-3.2), into

optical isomers, defeating the theory that only carbon compounds could

possess chirality.

Synthesis & Characterizations of Metal Complexes

69

Figure-3.2: Structure of hexol

3.2 PROPERTIES OF COORDINATION COMPOUNDS

Geometry

In coordination chemistry, a structure is first described by its coordination number,

the number of ligands attached to the metal (more specifically, the number of donor

atoms). Usually one can count the ligands attached, but sometimes even the counting

can become ambiguous. Coordination numbers are normally between two and nine,

but large numbers of ligands are not uncommon for the lanthanides and actinides. The

number of bonds depends on the size, charge, and electron configuration of the metal

ion and the ligands. Metal ions may have more than one coordination number.

Typically the chemistry of complexes is dominated by interactions between s and

p molecular orbitals of the ligands and the d orbitals of the metal ions. The s, p, and d

orbitals of the metal can accommodate 18 electrons. The maximum coordination

number for a certain metal is thus related to the electronic configuration of the metal

ion (to be more specific, the number of empty orbitals) and to the ratio of the size of

the ligands and the metal ion. Large metals and small ligands lead to high

coordination numbers, e.g. [Mo(CN)8]4−

. Small metals with large ligands lead to low

coordination numbers, e.g. Pt[P(CMe3)]2. Due to their large

size, lanthanides, actinides and early transition metals tend to have high coordination

numbers.

C o

N H 3

N H 3 O H

H 3 N

O H H 3 N C o

O H

O H

C o

C o

N H 3

N H 3

N H 3 H 3 N

N H 3 H O

N H 3 H O

N H 3 H 3 N

( S O 4 2 - ) 3

+ 6

Synthesis & Characterizations of Metal Complexes

70

Different ligand structural arrangements result from the coordination number. Most

structures follow the points-on-a-sphere pattern (or, as if the central atom were in the

middle of a polyhedron where the corners of that shape are the locations of the

ligands), where orbital overlap (between ligand and metal orbitals) and ligand-ligand

repulsions tend to lead to certain regular geometries. The most observed geometries

are listed below, but there are many cases that deviate from a regular geometry, e.g.

due to the use of ligands of different types (which results in irregular bond lengths;

the coordination atoms do not follow a points-on-a-sphere pattern), due to the size of

ligands, or due to electronic effects (e.g., Jahn–Teller distortion):

Linear for two-coordination

Trigonal planar for three-coordination

Tetrahedral or square planar for four-coordination

Trigonal bipyramidal or square pyramidal for five-coordination

Octahedral (orthogonal) or trigonal prismatic for six-coordination

Pentagonal bipyramidal for seven-coordination

Square antiprismatic for eight-coordination

Tri-capped trigonal prismatic (Triaugmented triangular prism) for nine-

coordination.

Color

Metal complexes often have spectacular colors caused by electronic transitions by the

absorption of light. For this reason they are often applied as pigments. Most

transitions that are related to colored metal complexes are either d–d

transitions or charge transfer bands.

In a d–d transition, an electron in a d orbital on the metal is excited by a photon to

another d orbital of higher energy. A charge transfer band entails promotion of an

electron from a metal-based orbital into an empty ligand-based orbital (Metal-to-

Ligand Charge Transfer or MLCT). The converse also occurs: excitation of an

electron in a ligand-based orbital into an empty metal-based orbital (Ligand to Metal

Charge Transfer or LMCT). These phenomena can be observed with the aid of

electronic spectroscopy; also known as UV-Vis [15]. For simple compounds with

Synthesis & Characterizations of Metal Complexes

71

high symmetry, the d–d transitions can be assigned using Tanabe–Sugano diagrams.

These assignments are gaining increased support with computational chemistry.

Magnetism

Metal complexes that have unpaired electrons are magnetic. Considering only

monometallic complexes, unpaired electrons arise because the complex has an odd

number of electrons or because electron pairing is destabilized. Transition metal

compounds are paramagnetic when they have one or more unpaired d electrons [16].

Thus, monomeric Ti(III) species have one "d-electron" and must be (para)magnetic,

regardless of the geometry or the nature of the ligands. Ti(II), with two d-electrons,

forms some complexes that have two unpaired electrons and others with none. This

effect is illustrated by the compounds TiX2[(CH3)2PCH2CH2P(CH3)2]2: when X = Cl,

the complex is paramagnetic (high-spin configuration), whereas when X = CH3, it is

diamagnetic (low-spin configuration). It is important to realize that ligands provide an

important means of adjusting the ground state properties.

In bi- and polymetallic complexes, in which the individual centers have an odd

number of electrons or that are high-spin, the situation is more complicated. If there is

interaction (either direct or through ligand) between the two (or more) metal centers,

the electrons may couple (antiferromagnetic coupling, resulting in a diamagnetic

compound), or they may enhance each other (ferromagnetic coupling). When there is

no interaction, the two (or more) individual metal centers behave as if in two separate

molecules.

Isomerism

Isomers are two or more compounds that have the same chemical formula but a

different arrangement of atoms. Because of the different arrangement of atoms, they

differ in one or more physical or chemical properties. The arrangement of the ligands

is fixed for a given complex, but in some cases it is mutable by a reaction that forms

another stable isomer.

There exist many kinds of isomerism in coordination complexes, just as in many other

compounds. Two principal types of isomerism are known among coordination

compounds. Each of which can be further subdivided.

Synthesis & Characterizations of Metal Complexes

72

a) Stereoisomerism

i. Geometrical isomerism

ii. Optical isomerism

b) Structural isomerism

i. Linkage isomerism

ii. Coordination isomerism

iii. Ionisation isomerism

iv Solvate isomerism

Stereoisomers have the same chemical formula and chemical bonds but they have

different spatial arrangement. Structural isomers have different bonds.

3.3 USEFULNESS OF COORDINATION COMPOUNS

3.3.1 COORINATION COMPOUNDS IN NATURE

Coordination compounds and transition metals are widespread in nature. Naturally

occurring coordination compounds are vital to living organisms. Metal complexes

play a variety of important roles in biological systems. They are most commonly

encountered as an integral component to proteins, especially the class of proteins that

can perform chemical reactions, termed enzymes.

Many enzymes, the naturally occurring catalysts that regulate biological processes,

are metal complexes (metalloenzymes); for example, carboxypeptidase, a hydrolytic

enzyme important in digestion, contains a zinc ion coordinated to several amino acid

residues of the protein. Another enzyme, catalase, which is an efficient catalyst for the

decomposition of hydrogen peroxide, contains iron-porphyrin complexes. In both

cases, the coordinated metal ions are probably the sites of catalytic activity. Structure

of simple porphyrin and heme B group of hemoglobin are shown in figure-3.3.

Synthesis & Characterizations of Metal Complexes

73

Figure-3.3: Structures of porphyrins

Hemoglobin also contains iron-porphyrin complexes, its role as an oxygen carrier

being related to the ability of the iron atoms to coordinate oxygen molecules

reversibly. Other biologically important coordination compounds

include chlorophyll (a magnesium-porphyrin complex) (Figure-3.4) and vitamin B12

(Figure-3.5), a complex of cobalt with a macrocyclic ligand known as corrin.

Figure-3.4: Structure of chlorophyll

Proteins, polysaccharides, and polynucleic acids are excellent polydentate ligands for

many metal ions. Organic compounds such as the amino acids glutamic acid

and histidine, organic diacids such as malate, and polypeptides such

N

N N

N

R

M g

O O O

O O

C h l o r o p h y l l a , R = C H 3 C h l o r o p h y l l b , R = C H O

N

N N

N

H 3 C

C H 2 C H 3

C H 2

C H 3

C O O H H O O C

H 3 C

F e

N

N H N

H N

S i m p l e p o r p h y r i n

H e m e B g r o u p o f h e m o g l o b i n

Synthesis & Characterizations of Metal Complexes

74

as phytochelatin are also typical chelators. In addition to these adventitious chelators,

several biomolecules are specifically produced to bind certain metals [17-19].

Figure-3.5: Structure of vitamin B12

Many microbial species produce water-soluble pigments that serve as chelating

agents, termed siderophores. For example, species of Pseudomonas are known to

secrete pyocyanin and pyoverdin that bind iron. Enterobactin, produced by E. coli, is

the strongest chelating agent known.

3.3.2 CORDINATION COMPOUNDS IN INDUSTRY

The applications of coordination compounds in chemistry and technology are

numerous and diverse. The brilliant and intense colors of many coordination

compounds, such as Prussian blue, render them of great value

as dyes and pigments. Phthalocyanine complexes (e.g., copper phthalocyanine),

containing large-ring ligands closely related to the porphyrins (Figure-3.6), constitute

an important class of dyes for fabrics.

N

N N

N H

H 2 N O C

C O N H 2

C O N H 2

C O N H 2

N H

O P

H 2 N O C

H 2 N O C

O

O

O O

O

H O N

N

H O

C o +

R = 5 ' - d e o x y a d e n o s y l , M e , O H , C N

Synthesis & Characterizations of Metal Complexes

75

Figure-3.6: Structures of phthalocyanine

Several important hydrometallurgical processes utilize metal

complexes. Nickel, cobalt and copper can be extracted from their ores as ammine

complexes using aqueous ammonia. Differences in the stabilities and solubilities of

the ammine complexes can be exploiting in selective precipitation procedures that

bring about separation of the metals. The purification of nickel can be effected by

reaction with carbon monoxide to form the volatile tetracarbonylnickel complex,

which can be distilled and thermally decomposed to deposit the pure metal.

Aqueous cyanide solutions usually are employed to separate gold from its ores in the

form of the tremendously stable dicyanoaurate(−1) complex. Cyanide complexes also

find application in electroplating.

There are a number of ways in which coordination compounds are used in the analysis

of various substances. These include

(1) The selective precipitation of metal ions as complexes—for example,

nickel(2+) ion as the dimethylglyoxime complex (Figure-3.7)

(2) The formation of coloured complexes, such as the tetrachlorocobaltate(2−)

ion, which can be determined spectrophotometrically—that is, by means of

their light absorption properties, and

(3) The preparation of complexes, such as metal acetylacetonates, which can be

separated from aqueous solution by extraction with organic solvents.

N H

N

N

H N

N

N

N

N

N

N

N

N

N

N

N

N

P h t h a l o c y a n i n e

C u

C o p p e r p h t h a l o c y a n i n e

Synthesis & Characterizations of Metal Complexes

76

Figure-3.7: Structure of dimethylglyoxime

In certain circumstances, the presence of metal ions is undesirable, as, for example,

in water, in which calcium (Ca2+

) and magnesium (Mg2+

) ions cause hardness. In such

cases the undesirable effects of the metal ions frequently can be eliminated by

“sequestering” the ions as harmless complexes through the addition of an appropriate

complexing reagent.

Ethylenediaminetetraacetic acid (EDTA) (Figure-3.8) forms very stable complexes,

and it is widely used for this purpose. Its applications include water softening (by

tying up Ca2+

and Mg2+

) and the preservation of organic substances, such as vegetable

oils and rubber, in which case it combines with traces of transition metal ions that

would catalyze oxidation of the organic substances.

Chelators are used in producing nutritional supplements, fertilizers, chemical analysis,

as water softeners, commercial products such as shampoos and food preservatives,

medicine, heavy metal detox, and numerous additional industrial applications.

N i

N

N N

N

O O

O O

C

C C

C

H 3 C

H 3 C

C H 3

C H 3

H

H

d i m e t h y l g l y o x i m e c o m p l e x

Synthesis & Characterizations of Metal Complexes

77

Figure-3.8: Structure of EDTA & it’s metal chelate

For the overall health of the plants some micronutrients such as manganese, iron, zinc,

copper - are required. Metal chelate compounds are common components of fertilizers

to provide micronutrients.

A technological and scientific development of major significance was the discovery in

1954 that certain complex metal catalysts— namely, a combination of titanium

trichloride (TiCl3) and triethylaluminum (Al(C2H5)3)—bring about

the polymerizations of organic compounds with carbon-carbon double bonds under

mild conditions to form polymers of high molecular weight and highly ordered

(stereoregular) structures. Certain of these polymers are of great commercial

importance because they are used to make many kinds of fibres, films, and plastics.

Other technologically important processes based on metal complex catalysts include

the catalysis by metal carbonyls, such as hydridotetracarbonylcobalt, of the so-

called hydroformylation of olefins—i.e., of their reactions with hydrogen and carbon

monoxide to form aldehydes—and the catalysis by tetrachloropalladate(2−) ions of

the oxidation of ethylene in aqueous solution to acetaldehyde.

3.3.3 COORDINATION COMPOUNDS IN MEDICINE

Main use of coordination compounds in medicine is in chelation therapy.

Chelation describes a particular way that ions and molecules bind metal

ions. According to the International Union of Pure and Applied Chemistry (IUPAC),

Chelation therapy is the use of chelating agents to detoxify poisonous metal agents

such as mercury, arsenic, and lead by converting them to a chemically inert form that

H O

N N

O H

O H O H O

O

O

O

E t h y l e n e d i a m i n e t e t r a a c e t i c a c i d

N

O -

N O -

O -

O -

O

O

O

O

M

M e t a l - E D T A c h e l a t e

Synthesis & Characterizations of Metal Complexes

78

can be excreted without further interaction with the body, and was approved by

the U.S. Food and Drug Administration in 1991. Chelation therapy is most frequently

given into a vein, either as a short injection or over a period of two to four hours. A

typical treatment cycle may include twenty injections or infusions spread over ten to

twelve weeks. Chelation therapy can also be given by mouth.

The human body cannot break down heavy metals, which can build up to toxic levels

in the body and interfere with normal functioning. EDTA and other chelating drugs

lower the levels of metals such as lead, mercury, cadmium, and zinc in blood by

attaching to the heavy metal molecules, which helps the body to remove them through

urination.

Because EDTA can reduce the amount of calcium in the bloodstream, some

practitioners suggest chelation therapy may help reopen arteries blocked by mineral

deposits, a condition called atherosclerosis or hardening of the arteries. They claim it

is an effective and less expensive alternative to coronary bypass surgery, angioplasty

and other techniques designed to unclog blocked arteries.

Chelation therapy has also been promoted as an alternative treatment for many

unrelated conditions, such as gangrene, thyroid disorders, multiple sclerosis, muscular

dystrophy, psoriasis, diabetes, arthritis, Alzheimer’s disease, and the improvement of

memory, sight, hearing and smell.

Some alternative practitioners further claim chelation therapy can be used as a cancer

treatment. They claim it can remove "environmental toxins" from the body and block

the production of harmful molecules called free radicals that can cause cell damage.

In alternative medicine, chelation is used as a treatment for autism, although this

practice is controversial due to the absence of scientific plausibility, lack of FDA

approval, and its potentially deadly side-effects [20].

Although they can be beneficial in cases of heavy metal poisoning, chelating agents

can also be dangerous. Use of disodium EDTA instead of calcium EDTA has resulted

in fatalities due to hypocalcemia. Chelation therapy may produce toxic effects,

including kidney damage, irregular heartbeat, and swelling of the veins. It may also

Synthesis & Characterizations of Metal Complexes

79

cause nausea, vomiting, diarrhea, and temporary lowering of blood pressure. Since the

therapy removes minerals from the body, there is a risk of developing low calcium

levels (hypocalcemia) and bone damage. Chelation therapy may also impair the

immune system and decrease the body's ability to produce insulin.

Dimercaprol (British Anti-lewisite, or BAL) was the first widely used chelating agent

as a cure for Lewisite, the arsenic based poison gas. The most commonly used

chelating agents (Figure-3.8) today are :

Dimercaptosuccinic acid (DMSA)

EDTA (usually in its calcium disodium form)

Dimercapto-propane sulfonate (DMPS)

Alpha lipoic acid (ALA)

Diethylene triamine pentaacetic acid (DTPA)

Dimercaprol (BAL)

DMSA and BAL – both dithiols, bind metals through adjacent –SH groups, much like

the proteins the metals would otherwise bind to in vivo. DMSA, specifically, can

cross the blood-brain barrier and is used to sequester heavy metals in brain.

Metal complexes are also useful in other medical applications. For example, Chelate

complexes of gadolinium are often used as contrast agents in MRI scans.

Figure-3.9: Structures of commonly used chelating agents

S O -

S H

S H

H 3 C

O

O

D i m e r c a p t o p r o p a n e s u l f o n a t e

S S

O H

O

H

A l p h a l i p o i c a c i d

N N

N

O

O H

O H

O

O H

O

H O O O

O H

D i e t h y l e n e t r i a m i n e p e n t a a c e t i c a c i d

Synthesis & Characterizations of Metal Complexes

80

Figure-3.9: Structures of commonly used chelating agents

3.4 CURRENT WORK

Many coumarins show distinct physiological photodynamic and bacteriostatic

activities [21] and placed for many diverse uses. Their chelating characteristics have

long been observed and the bacteriostatic activity seems to be due to chelation. The

physicochemical studies [22,23] of the coumarins with chelating group at appropriate

position and their metal complexes reveal that the ligand can be used as potential

analytical reagents [24].

Earlier work reported that some drugs showed increased activity, when administered

as metal complexes rather than as organic compounds [25,26]. Moreover, a lot of

research has been done on nitrogen containing ligands which is also known as Schiff

bases compare to ligands containing oxygen & sulfur.

Going through the literature survey and considering the vital role of the coumarin

derivatives in biological applications and diagnostic parameters, the present work was

undertaken to prepare, Fe(II), Co(II), Ni(II) and Cu(II) complexes with various

substituted and unsubstituted 3-acetyl-4-hydroxy-pyrano[3,2-c]chromene-2,5-dione

and 4-hydroxy-3-(3-oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione as ligands; which

was previously synthesized (as described in chapter-2). All metal complexes were

characterized by UV, FT-IR, mass spectra, 1H NMR and elemental analyses. They

were also subjected to various biological activities viz., antimicrobial & DNA binding

ability to know the biological properties of synthesized complexes.

3.4.1 LIST OF LIGANDS USED FOR THE SYNTHESIS OF METAL

COMPLEXES

1) 3-acetyl-4-hydroxy-pyrano[3,2-c]chromene-2,5-dione (LI) (sample code - 13)

H O

O

O H

S H

S H O

D M S A

H S O H

S H

B A L

Synthesis & Characterizations of Metal Complexes

81

2) 3-acetyl-4-hydroxy-9-methylpyrano[3,2-c]chromene-2,5-dione (LII

)

(sample code-23)

3) 3-acetyl-4-hydroxy-7-methylpyrano[3,2-c]chromene-2,5-dione (LIII

)

(sample code-33)

4) 3-acetyl-4-hydroxy-8-methylpyrano[3,2-c]chromene-2,5-dione (LIV

)

(sample code -43)

5) 3-acetyl-4-hydroxy-8,10-dimethylpyrano[3,2-c]chromene-2,5-dione (LV)

(sample code-53)

6) 3-acetyl-4-hydroxy-7,8-dimethylpyrano[3,2-c]chromene-2,5-dione (LVI

) (sample

code-63)

7) 4-hydroxy-3-(3-oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LVII

)

(sample code-14)

8) 4-hydroxy-9-methyl-3-(3-oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LVIII

)

(sample code-24)

9) 4-hydroxy-7-methyl-3-(3-oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LIX

)

(sample code-34)

10) 4-hydroxy-8-methyl-3-(3-oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LX)

(sample code-44)

11) 4-hydroxy-8,10-dimethyl-3-(3-oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione

(LXI

) (sample code-54)

12) 4-hydroxy-7,8-dimethyl-3-(3-oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione

(LXII

) (sample code-64)

3.5 REACTION SCHEME

Scheme-3.5.1: Reaction of 3-acetyl-4-hydroxy-pyrano[3,2-c]chromene-2,5-dione

O

R 4

R 3

R 2

R 1

O

O

O H

O

C O C H 3

O

R 4

R 3

R 2

R 1

O

O

O H

O

C - C H 3

O

M + 2

e t h a n o l

m e t a l

W h e r e , R 1 , R 2 , R 3 & R 4 = H O r C H 3 M = F e ( I I ) , C o ( I I ) , N i ( I I ) , o r C u ( I I )

Synthesis & Characterizations of Metal Complexes

82

Scheme-3.5.2: Reaction of 4-hydroxy-3-(3-oxobutanoyl)pyrano[3,2-c]chromene-2,5-

dione

Figure-3.10: Possible structure of metal complex

3.6 EXPERIMENTAL

3.6.1 ANALYSIS PROTOCOLS

All chemicals used were of analytical reagent (AR) grade and of the highest purity

available. All the melting points were determined in open glass capillaries in a liquid

paraffin-bath. All metal complexes char above temperature 270°C. IR spectra were

O

R 4

R 3

R 2

R 1

O

O

O H

O

C - C H 3 O

M + 2

O

O O

H O

R 1

R 2

R 3

R 4

O

H 3 C - C

O

O

R 4

R 3

R 2

R 1

O

O

O H

O

C - C H 2 C O C H 3 O

M + 2

O

O O

H O

R 1

R 2

R 3

R 4

O

H 3 C O C H 2 C - C

O

W h e r e , R 1 , R 2 , R 3 & R 4 = H O r C H 3 M = F e ( I I ) , C o ( I I ) , N i ( I I ) , o r C u ( I I )

s t r u c t u r e - I s t r u c t u r e - I I

H 2 O H 2 O H 2 O H 2 O

O

R 4

R 3

R 2

R 1

O

O

O H

O

C O C H 2 C O C H 3

O

R 4

R 3

R 2

R 1

O

O

O H

O

C - C H 2 C O C H 3

O

e t h a n o l m e t a l

M + 2 W h e r e , R 1 , R 2 , R 3 & R 4 = H O r C H 3 M = F e ( I I ) , C o ( I I ) , N i ( I I ) , o r C u ( I I )

Synthesis & Characterizations of Metal Complexes

83

recorded in Shimadzu 435-IR instrument using KBr Powder method. UV analysis

was carried out using Shimadzu UV 1800, shimadzu pte. Ltd. Japan. Mass spectra

were recorded on GCMS-QP2010 spectrometer (EI method). The NMR Spectra

were recorded on BRUKER NMR Spectrometer (300 MHz). Elemental analysis of

the all the synthesized compounds was carried out on Elemental Perkin- Elmer 2400

CHN elemental Analyzer Model 1106. All the results are in agreements with the

structures assigned. Thermo gravimetric analysis of representative metal complexes

was carried out within a temperature range from room temperature up to 800 °C.

3.6.2 METHOD OF PREPARATION FOR METAL COMPLEXES

The metal solutions (0.1M) were prepared by dissolving metal salt (ferrous

ammonium sulphate and chloride of cobalt, nickel & copper) in distilled water and

standardized with 0.1M EDTA solution. Reaction of standardized metal solution

(10ml) was carried out with ligand solution (20ml) for two hours in water bath at

100°C. Few drops of ammonium hydroxide were added to the reaction mixture to

maintain the pH 10.5-11. Precipitates obtained were filtered, washed with water and

alcohol, dried and recrystalised with DMSO.

3.6.3 CONDUCTIVITY

The conductivity of metal complexes was determined using Systronic Conductivity

Bridge. It was dissolved in DMF and conductivity was measured. Conductivity of the

DMF along was measured and solution of the complexes in DMF with different

concentration was measured. The molar conductivity was calculated using the

formula

Where, K = Conductivity of the solution of the complexes in DMF.

C = Concentration of the complexes (10-3

M).

The conductivity data are presented in Table:3.2 to 3.13 and the data indicates that

the complexes are non-electrolyte in nature [27].

Synthesis & Characterizations of Metal Complexes

84

3.7 PHYSICAL DATA

3.7.1 PHYSICAL DATA TABLES OF SYNTHESIZED COMPOUNDS

Figure-3.11: General structure of complexes of 3-acetyl-4-hydroxy-

pyrano[3,2-c]chromene-2,5-dione (LI)

Table:3.2 Complexes of 3-acetyl-4-hydroxy-pyrano[3,2-c]chromene-2,5-dione (LI)

Figure-3.12: General structure of complexes of 3-acetyl-4-hydroxy-9-

methylpyrano[3,2-c]chromene-2,5-dione (LII

)

Complex Sample Molecular Molecular Molar Color

M[LI(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LI(H2O)]2 136 C28H22O14Fe 638 52.75/52.69 3.62/3.47 34.91/35.09 8.89/8.75 11.3 Brown

Co[LI(H2O)]2 137 C28H22O14Co 641 52.61/52.43 3.29/3.46 35.11/34.92 9.18/9.19 14.25 Dark Brown

Ni[LI(H2O)]2 138 C28H22O14Ni 641 52.32/52.45 3.31/3.46 35.08/34.94 9.03/9.15 9.87 Light Brown

Cu[LI(H2O)]2 139 C28H22O14Cu 646 51.92/52.06 3.56/3.43 34.52/34.67 9.72/9.84 12.52 Dark Brown

Elemental analysis(%)

Found/Calcd.

O O

O

O H

O C - C H 3 O

M + 2

O

O O

H O

O H 3 C - C

O

W h e r e , M =

F e ( I I ) , C o ( I I ) ,

N i ( I I ) , o r C u ( I I )

H 2 O H 2 O

H 3 C

C H 3

O O

O

O H

O C - C H 3 O

M + 2

O

O O

H O

O H 3 C - C

O

W h e r e , M =

F e ( I I ) , C o ( I I ) ,

N i ( I I ) , o r C u ( I I )

H 2 O H 2 O

Synthesis & Characterizations of Metal Complexes

85

Table:3.3 Complexes of 3-acetyl-4-hydroxy-9-methylpyrano[3,2-c]chromene-2,5-

dione (LII

)

Figure-3.13: General structure of complexes of 3-acetyl-4-hydroxy-7-

methylpyrano[3,2-c]chromene-2,5-dione (LIII

)

Table:3.4 Complexes of 3-acetyl-4-hydroxy-7-methylpyrano[3,2-c]chromene-2,5-

dione (LIII

)

Complex Sample Molecular Molecular Molar Color

M[LII

(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LII(H2O)]2 236 C30H26O14Fe 666 54.23/54.07 4.2/3.93 33.49/33.61 8.1/8.38 9.93 Yellowish Brown

Co[LII(H2O)]2 237 C30H26O14Co 669 53.89/53.82 3.79/3.91 33.38/33.46 8.94/8.8 11.58 Light Brown

Ni[LII(H2O)]2 238 C30H26O14Ni 668 53.9/53.84 3.83/3.92 33.53/33.47 8.72/8.77 14.63 Orange

Cu[LII(H2O)]2 239 C30H26O14Cu 673 53.52/53.45 3.96/3.89 33.15/33.23 9.36/9.43 13.76 Dark Brown

Elemental analysis(%)

Found/Calcd.

Complex Sample Molecular Molecular Molar Color

M[LIII

(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LIII

(H2O)]2 336 C30H26O14Fe 666 54.25/54.07 3.9/3.93 33.51/33.61 8.24/8.38 10.59 Dark Brown

Co[LIII

(H2O)]2 337 C30H26O14Co 669 53.93/53.82 3.75/3.91 33.33/33.46 8.96/8.8 13.78 Light Orange

Ni[LIII

(H2O)]2 338 C30H26O14Ni 668 53.92/53.84 3.75/3.92 33.58/33.47 8.67/8.77 9.68 Yellowish Brown

Cu[LIII

(H2O)]2 339 C30H26O14Cu 673 53.56/53.45 4.02/3.89 33.09/33.23 9.39/9.43 12.93 Brown

Found/Calcd.

Elemental analysis(%)

O O

O

O H

O

C - C H 3 O

M + 2

O

O O

H O

O H 3 C - C

O

W h e r e , M = F e ( I I ) , C o ( I I ) , N i ( I I ) , o r C u ( I I )

H 2 O H 2 O

C H 3

C H 3

Synthesis & Characterizations of Metal Complexes

86

Figure-3.14: General structure of complexes of 3-acetyl-4-hydroxy-8-

methylpyrano[3,2-c]chromene-2,5-dione (LIV

)

Table:3.5 Complexes of 3-acetyl-4-hydroxy-8-methylpyrano[3,2-c]chromene-2,5-

dione (LIV

)

Figure-3.15: General structure of complexes of 3-acetyl-4-hydroxy-8,10-

dimethylpyrano[3,2-c]chromene-2,5-dione (LV)

Complex Sample Molecular Molecular Molar Color

M[LIV

(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LIV

(H2O)]2 436 C30H26O14Fe 666 54.19/54.07 4.12/3.93 33.54/33.61 8.15/8.38 10.14 Dark Brown

Co[LIV

(H2O)]2 437 C30H26O14Co 669 53.75/53.82 3.83/3.91 33.25/33.46 9.15/8.8 12.07 Light Green

Ni[LIV

(H2O)]2 438 C30H26O14Ni 668 53.96/53.84 3.78/3.92 33.61/33.47 8.66/8.77 11.85 Light Orange

Cu[LIV

(H2O)]2 439 C30H26O14Cu 673 53.32/53.45 3.81/3.89 33.1/33.23 9.76/9.43 14.2 Dark Brown

Elemental analysis(%)

Found/Calcd.

O O

O

O H

O C - C H 3 O

M + 2

O

O O

H O

O H 3 C - C

O

W h e r e , M = F e ( I I ) , C o ( I I ) , N i ( I I ) , o r C u ( I I )

H 2 O H 2 O

H 3 C

C H 3

C H 3

C H 3

O O

O

O H

O

C - C H 3 O

M + 2

O

O O

H O

O H 3 C - C

O

W h e r e , M = F e ( I I ) , C o ( I I ) , N i ( I I ) , o r C u ( I I )

H 2 O H 2 O

H 3 C

C H 3

Synthesis & Characterizations of Metal Complexes

87

Table:3.6 Complexes of 3-acetyl-4-hydroxy-8,10-dimethylpyrano[3,2-c]chromene-

2,5-dione (LV)

Figure-3.16: General structure of complexes of 3-acetyl-4-hydroxy-7,8-

dimethylpyrano[3,2-c]chromene-2,5-dione (LVI

)

Table:3.7 Physical Data Table of complexes of 3-acetyl-4-hydroxy-7,10-

dimethylpyrano[3,2-c]chromene-2,5-dione (LVI

)

Complex Sample Molecular Molecular Molar Color

M[LV(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LV(H2O)]2 536 C32H26O12Fe 658 58.13/58.38 4.1/3.98 28.97/29.16 8.39/8.48 13.2 Reddish Brown

Co[LV(H2O)]2 537 C32H26O12Co 661 58.33/58.10 3.79/3.96 28.87/29.02 0 10.08 Green

Ni[LV(H2O)]2 538 C32H26O12Ni 661 57.91/58.12 3.86/3.69 29.31/29.04 8.72/8.88 11.32 Dark Brown

Cu[LV(H2O)]2 539 C32H26O12 Cu 666 57.92/57.7 4.15/3.93 28.65/28.82 9.31/9.54 9.15 Green

Elemental analysis(%)

Found/Calcd.

Complex Sample Molecular Molecular Molar Color

M[LVI

(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LVI

(H2O)]2 636 C32H26O12Fe 658 58.27/58.38 4.06/3.98 28.89/29.16 8.32/8.48 13.71 Dark Brown

Co[LVI

(H2O)]2 637 C32H26O12Co 661 57.87/58.10 3.74/3.96 29.42/29.02 9.11/8.91 10.6 Light Brown

Ni[LVI

(H2O)]2 638 C32H26O12Ni 661 58.34/58.12 3.86/3.69 29.24/29.04 8.96/8.88 11.83 Dark Brown

Cu[LVI

(H2O)]2 639 C32H26O12 Cu 666 57.39/57.7 4.28/3.93 29.19/28.82 9.78/9.54 9.85 Dark Brown

Elemental analysis(%)

Found/Calcd.

O O

O

O H

O

C - C H 3 O

M

O O

O

H O

O

H 3 C - C

O H 2 O O H 2

Synthesis & Characterizations of Metal Complexes

88

Figure-3.17: General structure of complexes of 4-hydroxy-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LVII

)

Table:3.8 Complexes of 4-hydroxy-3-(3-oxobutanoyl)pyrano[3,2-c]chromene-2,5-

dione (LVII

)

Figure-3.18: General structure of complexes of 4-hydroxy-9-methyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LVIII

)

Complex Sample Molecular Molecular Molar Color

M[LVII

(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LVII

(H2O)]2 146 C32H26O16Fe 722 53.04/53.2 3.78/3.63 35.68/35.44 7.52/7.73 12.38 Chocolate Brown

Co[LVII

(H2O)]2 147 C32H26O16Co 725 53.13/52.98 3.75/3.61 35.4/35.29 8.26/8.12 13.57 Light Brown

Ni[LVII

(H2O)]2 148 C32H26O16Ni 725 52.89/53 3.55/3.61 35.14/35.3 7.94/8.09 11.08 Dark Brown

Cu[LVII

(H2O)]2 149 C32H26O16Cu 730 52.53/52.64 3.68/3.59 34.88/35.06 8.92/8.7 14.36 Greenish Brown

Elemental analysis(%)

Found/Calcd.

O O

O

O H

O

C - C H 2 C O C H 3 O

M + 2

O

O O

H O

O H 3 C O C H 2 C - C

O

H 2 O H 2 O

W h e r e , M = F e ( I I ) , C o ( I I ) , N i ( I I ) , o r C u ( I I )

H 3 C

C H 3

O O

O

O H

O C - C H 2 C O C H 3 O

M + 2

O

O O

H O

O H 3 C O C H 2 C - C

O H 2 O H 2 O

W h e r e , M = F e ( I I ) , C o ( I I ) , N i ( I I ) , o r C u ( I I )

Synthesis & Characterizations of Metal Complexes

89

Table:3.9 Complexes of 4-hydroxy-9-methyl-3-(3-oxobutanoyl)pyrano[3,2-c]

chromene-2,5-dione (LVIII

)

Figure-3.19: General structure of complexes of 4-hydroxy-7-methyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LIX

)

Table:3.10 Physical Data Table of complexes of 4-hydroxy-7-methyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LIX

)

Complex Sample Molecular Molecular Molar Color

M[LVIII

(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LVIII

(H2O)]2 246 C34H30O16Fe 750 54.35/54.42 3.94/4.03 34.2/34.11 7.51/7.44 10.24 Reddish Brown

Co[LVII

(H2O)]2 247 C34H30O16Co 753 54.27/54.19 3.91/4.01 34.06/33.97 7.78/7.82 13.49 Yellowish Brown

Ni[LVIII

(H2O)]2 248 C34H30O16Ni 753 54.33/54.21 4.15/4.01 34.06/33.98 7.46/7.79 12.4 Green

Cu[LVIII

(H2O)]2 249 C34H30O16Cu 758 53.98/53.86 4.1/3.99 33.81/33.77 8.11/8.38 15.2 Dark Brown

Found/Calcd.

Elemental analysis(%)

Complex Sample Molecular Molecular Molar Color

M[LIX

(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LIX

(H2O)]2 346 C34H30O16Fe 750 54.51/54.42 3.84/4.03 34.24/34.11 7.58/7.44 14.19 Brown

Co[LIX

(H2O)]2 347 C34H30O16Co 753 54.21/54.19 3.93/4.01 34.01/33.97 7.73/7.82 10.54 Reddish Brown

Ni[LIX

(H2O)]2 348 C34H30O16Ni 753 54.39/54.21 4.09/4.01 33.92/33.98 7.58/7.79 13.69 Green

Cu[LIX

(H2O)]2 349 C34H30O16Cu 758 53.95/53.86 4.12/3.99 33.86/33.77 8.2/8.38 12.73 Dark Brown

Elemental analysis(%)

Found/Calcd.

O O

O

O H

O

C - C H 2 C O C H 3 O

M + 2

O

O O

H O

O H 3 C O C H 2 C - C

O

H 2 O H 2 O

W h e r e , M = F e ( I I ) , C o ( I I ) , N i ( I I ) , o r C u ( I I )

C H 3

C H 3

Synthesis & Characterizations of Metal Complexes

90

Figure-3.20: General structure of complexes of 4-hydroxy-8-methyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LX)

Table:3.11 Complexes of 4-hydroxy-8-methyl-3-(3-oxobutanoyl)pyrano[3,2-c]

chromene-2,5-dione (LX)

Figure-3.21: General structure of complexes of 4-hydroxy-8,10-dimethyl-3-

(3-oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LXI

)

Complex Sample Molecular Molecular Molar Color

M[LX(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LX(H2O)]2 446 C34H30O16Fe 750 54.31/54.42 3.89/4.03 34.24/34.11 7.56/7.44 11.49 Dark brown

Co[LX(H2O)]2 447 C34H30O16Co 753 54.08/54.19 3.94/4.01 34.13/33.97 7.87/7.82 14.17 Brown

Ni[LX(H2O)]2 448 C34H30O16Ni 753 54.13/54.21 4.12/4.01 33.9/33.98 7.85/7.79 15.43 Yellowish Brown

Cu[LX(H2O)]2 449 C34H30O16Cu 758 54.02/53.86 4.08/3.99 33.83/33.77 8.07/8.38 13.98 Green

Elemental analysis(%)

Found/Calcd.

O O

O

O H

O

C - C H 2 C O C H 3 O

M + 2

O

O O

H O

O H 3 C O C H 2 C - C

O

H 2 O H 2 O

W h e r e , M = F e ( I I ) , C o ( I I ) , N i ( I I ) , o r C u ( I I )

H 3 C

C H 3

C H 3

C H 3

O O

O

O H

O C - C H 2 C O C H 3 O

M + 2

O

O O

H O

O H 3 C O C H 2 C - C

O

H 2 O H 2 O

W h e r e , M = F e ( I I ) , C o ( I I ) , N i ( I I ) , o r C u ( I I )

H 3 C

C H 3

Synthesis & Characterizations of Metal Complexes

91

Table:3.12 Complexes of 4-hydroxy-8,10-dimethyl-3-(3-oxobutanoyl)pyrano[3,2-c]

chromene-2,5-dione (LXI

)

Figure-3.22: General structure of complexes of 4-hydroxy-7,8-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LXII

)

Table:3.13 Complexes of 4-hydroxy-7,10-dimethyl-3-(3-oxobutanoyl)pyrano[3,2-

c]chromene-2,5-dione (LXII

)

Complex Sample Molecular Molecular Molar Color

M[LXI

(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LXI

(H2O)]2 546 C36H30O14Fe 742 57.96/58.24 3.92/4.07 30.02/30.17 7.68/7.52 15.49 Chocolate Brown

Co[LXI

(H2O)]2 547 C36H30O14Co 745 57.73/58 4.45/4.06 30.26/30.04 6.97/7.9 11.92 Dark brown

Ni[LXI

(H2O)]2 548 C36H30O14Ni 745 58.34/58.01 3.84/4.06 29.82/30.05 8.04/7.88 12.78 Yellowish Brown

Cu[LXI

(H2O)]2 549 C36H30O14Cu 750 58.1/57.64 4.47/4.03 30.07/29.86 9.03/8.47 10.97 Green

Elemental analysis(%)

Found/Calcd.

Complex Sample Molecular Molecular Molar Color

M[LXII

(H2O)]2 code Formula weight conductance

(g) C H O M mho cm2mol

-1

Fe[LXII

(H2O)]2 646 C36H30O14Fe 742 58.16/58.24 3.89/4.07 30.32/30.17 7.78/7.52 15.88 Dark brown

Co[LXII

(H2O)]2 647 C36H30O14Co 745 57.86/58 4.32/4.06 29.87/30.04 8.12/7.9 12 Yellowish brown

Ni[LXII

(H2O)]2 648 C36H30O14Ni 745 58.39/58.01 4.25/4.06 30.21/30.05 7.56/7.8 13.05 Green

Cu[LXII

(H2O)]2 649 C36H30O14Cu 750 57.42/57.64 3.73/4.03 29.93/29.86 8.83/8.47 11.24 Greenish Yellow

Elemental analysis(%)

Found/Calcd.

O O

O

O H

O

C - C H 2 C O C H 3

O F e

O O

O

H O

O

H 3 C O C H 2 C - C

O H 2 O O H 2

Synthesis & Characterizations of Metal Complexes

92

3.7.2 PROPERTIES OF SYNTHESIZED COMPOUNDS

Most of the metal complexes are soluble in DMF and DMSO while some of

them are partially soluble in it; while shows complete solubility in hot DMF

and DMSO.

All the metal complexes are insoluble in solvents like water, alcohol, acetic

acid, acetone, benzene, diethyl ether and hexane.

All the metal complexes are highly stable with respect to temperature. All of

them char above temperature 270°C. So, exact melting point is not recorded

for any of them.

3.8 SPECTRAL STUDY

3.8.1 ABSORPTION SPECTRA

Absorption spectra of metal complexes in UV and visible region were taken on

instrument UV 1800, shimadzu pte. Ltd. Japan by dissolving metal complexes in

DMSO, which shows a very weak band in the range of 741-749 nm, along with two

regular bands in the range of 266-332 nm.

3.8.2 INFRA RED SPECTRA

Infra Red spectra were taken on Shimadzu 435-IR instrument using KBr Powder

method. In case of metal complexes, position of OH bands remains almost unaffected

indicating that the enolic OH is not replaced during complex formation; while a much

broader band is may be due to presence of water molecule. In all the spectra of

complexes both aromatic and acetyl ketone frequencies shifted by ~15–20 cm-1

to the

lower energy region compared to the free ligand. This phenomenon appears may be

due to the coordination of the carbonyl oxygen to the metal ion. The carbonyl groups

are involved in bonding with the metal is further supported by the appearance of a

medium intensity bands in the region 476-486 cm-1

assignable to M-O vibrations [28].

3.8.3 1H NMR SPECTRA

1H NMR spectra of compounds were recorded on Bruker AC 500 MHz FT-NMR

Spectrometer using TMS (Tetramethyl Silane) as an internal standard and DMSO-d6

as a solvent. In the NMR spectra, various proton values like methylene (-CH2), methyl

Synthesis & Characterizations of Metal Complexes

93

(-CH3), aromatic protons (Ar-H) were observed. In complexes values for methyl (-

CH3) protons are seen between 2.258-2.795 ppm. The aromatic protons (Ar-H)

shows multiplets between 6.527-7.616 ppm. The hydroxyl proton (-OH) was

observed very broad at 9.924-10.287 ppm. The carboxyl proton (-COCH3) was

observed at 1.772-1.91 ppm, while (-COCH2COCH3) at 4.104-4.193 ppm.

3.8.4 MASS SPECTRA

The mass spectrum of compounds was recorded by GCMS-QP2010 spectrometer (EI

method). The mass spectrum of compounds were obtained by positive chemical

ionization mass spectrometry. The molecular ion peak and the base peak in all

compounds were clearly obtained in mass spectram study. The molecular ion peak

(M+) values are in good agreement with molecular formula of all the compounds

synthesized.

3.8.5 ELEMENTAL ANALYSIS

Elemental analysis of the synthesized compounds was carried out on Vario EL Carlo

Erba 1108 which showed calculated and found percentage values of Carbon,

Hydrogen,oxygen and metal in support of the structure of synthesized compounds.

The analytical data for individual compounds synthesized in this chapter is mentioned

here.

3.8.6 THERMO GRAVIMETRIC ANALYSIS

Thermo gravimetric analysis of representative metal complexes was carried out

within a temperature range from room temperature up to 800 °C. The data from

thermogravimetric analysis clearly indicated that the decomposition of the complex

proceed in several steps.

Hydration water molecules were lost in between 30 °C - 120 °C.

The coordinated water molecules were liberated in between 120 °C - 180 °C.

There is no change up to ~300 ºC after that there is a break in the curves due

to evaporation of 0.5 molecule of organic ligand, the remaining ligand is

removed from the coordination sphere at ~

Finally the metal oxides were formed above 600 °C. The decomposition was

complete at ~600 °C for the complex.

Synthesis & Characterizations of Metal Complexes

94

The degradation pathway for the complex may be represented as follows.

M[L(H2O)]2.nH2O 30-120 °C M[L(H2O)]2 + nH2O

M[L(H2O)]2 120-180 °C M[L]2 + (H2O)2

M[L]2 180-300 °C M[L] + L

M[L] 300-600°C MO + L

Where, M= Fe(II), Co(II), Ni(II) or Cu(II)

n= 0, 1 or 2

3.9 SPECTRAL CHARACTERISATION

Iron(II) 3-acetyl-4-hydroxy-8,10-dimethylpyrano[3,2-c]chromene-2,5-dione

(Sample code-536)

UV-Vis. (DMSO) λmax/nm: 288, 332, 746. IR (KBr) cm-1

: 3434 (-OH str), 1612 (-

C=O str), 1032 (=C-O str), 3271, 1552 (ring skeleton), 2923 (alkane C-H str), 1452

(alkane C-H def.), 679 (alkane =C-H bend), 1681 (α,β-unsaturation), 1086 (C-O-C

str). 1H NMR 500 MHz (DMSO-d6, ppm): 1.772 (s, 6H, -COCH3), 2.357-2.550 (s,

12H, -CH3), 6.412 (s, 1H, Ar-H), 7.241-7.392 (m, 4H, Ar-H), 10.287 (s, br, 1H, -OH).

Mass [m/e (%)], M. Wt.: 693, 642, 607, 535, 473, 424, 377, 342, 320, 291, 262, 228,

205, 171, 142, 117, 94, 66, 46. C, H, N analysis, (Found/Calculated): C,

58.13/58.38; H, 4.1/3.98; O, 28.97/29.16; Fe, 8.39/8.48. TGA wt. loss in % (temp.):

4.812 (299.5°C), 27.139 (430°C), 33.035 (800°C).

Cobalt (II) 3-acetyl-4-hydroxy-8,10-dimethylpyrano[3,2-c]chromene-2,5-dione

(Sample code-537)

UV-Vis. (DMSO) λmax/nm: 266, 332, 741. IR (KBr) cm-1

: 3421 (-OH str), 1603 (-

C=O str), 1030 (=C-O str), 3339, 1578 (ring skeleton), 2921 (alkane C-H str), 1473

(alkane C-H def.), 691 (alkane =C-H bend), 1701 (α,β-unsaturation), 1081 (C-O-C

str). 1H NMR 500 MHz (DMSO-d6, ppm): 1.84 (s, 6H, -COCH3), 2.312-2.608 (s,

12H, -CH3), 6.413 (s, 1H, Ar-H), 7.406-7.609 (m, 4H, Ar-H), 10.227 (s, br, 1H, -OH).

Mass [m/e (%)], M. Wt.: 696, 669, 642, 591, 535, 475, 426, 378, 340, 271, 260, 210,

182, 146, 112, 90, 64, 44. C, H, N analysis, (Found/Calculated): C, 58.33/58.10; H,

Synthesis & Characterizations of Metal Complexes

95

3.79/3.96; O, 28.87/29.02; Co, 9.06/8.91. TGA wt. loss in %(temp.): 6.684 (299°C),

14.063 (332°C), 27.957 (800°C).

Nickel(II) 4-hydroxy-8,10-dimethyl-3-(3-oxobutanoyl)pyrano[3,2-c]chromene-

2,5-dione (Sample code-548)

UV-Vis. (DMSO) λmax/nm: 266, 290, 749. IR (KBr) cm-1

: 3436 (-OH str), 1609 (-

C=O str), 1033 (=C-O str), 3287, 1530 (ring skeleton), 2924 (alkane C-H str), 1448

(alkane C-H def.), 669 (alkane =C-H bend), 1679 (α,β-unsaturation), 1086 (C-O-C

str). 1H NMR 500 MHz (DMSO-d6, ppm): 1.91 (s, 6H, -COCH3), 2.258-2.463 (s,

12H, -CH3), 4.104 (s, 3H, -COCH2CO-), 6.530-7.616 (m, 4H, Ar-H), 9.924 (s, br,

1H, -OH). Mass [m/e (%)], M. Wt.: 780, 747, 704, 661, 599, 573, 502, 445, 395,

370, 334, 265, 201, 164, 128, 107, 84, 59, 46. C, H, N analysis, (Found/Calculated):

C, 58.34/58.01; H, 3.84/4.06; O, 29.82/30.05; Ni, 8.04/7.88. TGA wt. loss in

%(temp.): 7.307 (234°C), 46.746 (411°C), 26.851 (800°C).

Copper(II) 4-hydroxy-8,10-dimethyl-3-(3-oxobutanoyl)pyrano[3,2-c]chromene-

2,5-dione (Sample code-549)

UV-Vis. (DMSO) λmax/nm: 266, 291, 748. IR (KBr) cm-1

: 3413 (-OH str), 1609 (-

C=O str), 1082 (=C-O str), 1659, 1538 (ring skeleton), 2924 (alkane C-H str), 1448

(alkane C-H def.), 671 (alkane =C-H bend), 1659 (α,β-unsaturation), 1082 (C-O-C

str). 1H NMR 500 MHz (DMSO-d6, ppm): 1.91 (s, 6H, -COCH3), 2.258-2.463 (s,

12H, -CH3), 4.104 (s, 3H, -COCH2CO-), 6.530-7.616 (m, 4H, Ar-H), 9.924 (s, br,

1H, -OH). Mass [m/e (%)], M. Wt.: 785, 749, 707, 658, 668, 560, 507, 448, 399,

361, 311, 260, 221, 166, 130, 108, 85, 60, 42. C, H, N analysis, (Found/Calculated):

C, 58.1/57.64; H, 4.47/4.03, O, 30.07/29.86, Cu, 9.03/8.47. TGA wt. loss in

%(temp.): 4.326 (242°C), 46.087 (368°C), 36.087 (800°C).

Synthesis & Characterizations of Metal Complexes

96

3.10 REPRESENTATIVE SPECTRA

3.10.1 UV & Visible spectrum of Iron(II) 3-acetyl-4-hydroxy-8,10-

dimethylpyrano[3,2-c]chromene-2,5-dione (Sample code-536)

3.10.2 IR spectrum of Iron(II) 3-acetyl-4-hydroxy-8,10-dimethylpyrano[3,2-

c]chromene-2,5-dione (Sample code-536)

Synthesis & Characterizations of Metal Complexes

97

3.10.3 NMR spectrum of Iron(II) 3-acetyl-4-hydroxy-8,10-dimethylpyrano[3,2-

c]chromene-2,5-dione (Sample code-536)

3.10.4 Mass spectrum of Iron(II) 3-acetyl-4-hydroxy-8,10-dimethylpyrano[3,2-

c]chromene-2,5-dione (Sample code-536)

Synthesis & Characterizations of Metal Complexes

98

3.10.5 UV & Visible spectrum of Cobalt(II) 3-acetyl-4-hydroxy-8,10-

dimethylpyrano[3,2-c]chromene-2,5-dione (Sample code-537)

3.10.6 IR spectrum of Cobalt(II) 3-acetyl-4-hydroxy-8,10-dimethylpyrano[3,2-

c]chromene-2,5-dione (Sample code-537)

Synthesis & Characterizations of Metal Complexes

99

3.10.7 NMR spectrum of Cobalt(II) 3-acetyl-4-hydroxy-8,10-dimethylpyrano[3,2-

c]chromene-2,5-dione (Sample code-537)

3.10.8 Mass spectrum of Cobalt(II) 3-acetyl-4-hydroxy-8,10-dimethylpyrano[3,2-

c]chromene-2,5-dione (Sample code-537)

Synthesis & Characterizations of Metal Complexes

100

3.10.9 UV & Visible spectrum of Nickel(II) 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-548)

3.10.10 IR spectrum of Nickel(II) 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-548)

Synthesis & Characterizations of Metal Complexes

101

3.10.11 NMR spectrum of Nickel(II) 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-548)

3.10.12 Mass spectrum of Nickel(II) 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-548)

Synthesis & Characterizations of Metal Complexes

102

3.10.13 UV & Visible spectrum of Copper(II) 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-549)

3.10.14 IR spectrum of Copper(II) 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-549)

Synthesis & Characterizations of Metal Complexes

103

3.10.15 NMR spectrum of Copper(II) 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-549)

3.10.16 Mass spectrum of Copper(II) 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-549)

Synthesis & Characterizations of Metal Complexes

104

3.10.17 Representative TGA spectra

(I) TGA spectra of Iron(II) complex of 3-acetyl-4-hydroxy-8,10-

dimethylpyrano[3,2-c]chromene-2,5-dione (Sample code-536)

The spectra shows total 84.996 % weight loss up to 800 °C temperature. The

degradation pathway for the complex may be represented as follows.

Fe[LV(H2O)]2 2O 30-120 °C Fe[L

V(H2O)]2 + nH2O

Fe[LV(H2O)]2 120-180 °C Fe[L

V]2 + (H2O)2

Fe[LV]2 180-300 °C Fe[L

V] + L

V

Fe[LV] 300-600°C FeO + L

V

O O

O

O H

O O F e

O O

O

H O

O O H 2 O O H 2

C H 3

H 3 C

Synthesis & Characterizations of Metal Complexes

105

(II) TGA spectra of Cobalt (II) complex of 3-acetyl-4-hydroxy-8,10-

dimethylpyrano[3,2-c]chromene-2,5-dione (Sample code-537)

The spectra shows total 48.704 % weight loss up to 800 °C temperature. The

degradation pathway for the complex may be represented as follows.

Co[LV(H2O)]2 . nH2O 30-120 °C Co[L

V(H2O)]2 + nH2O

Co[LV(H2O)]2 120-180 °C Co[L

V]2 + (H2O)2

Co[LV]2 180-300 °C Co[L

V] + L

V

Co[LV] 300-600 °C CoO + L

V

O O

O

O H

O C - C H 3 O

C o

O O

O

H O

O H 3 C - C

O H 2 O O H 2

Synthesis & Characterizations of Metal Complexes

106

(III) TGA spectra of Nickle(II) complex of 3-acetyl-4-hydroxy-8,10-

dimethylpyrano[3,2-c]chromene-2,5-dione (Sample code-538)

The spectra shows total 75.865 % weight loss up to 800 °C temperature. The

degradation pathway for the complex may be represented as follows.

Ni[LV(H2O)]2 2O 30-120 °C Ni[L

V(H2O)]2 + nH2O

Ni[LV(H2O)]2 120-180 °C Ni[L

V]2 + (H2O)2

Ni[LV]2 180-300 °C Ni[L

V] + L

V

Ni[LV] 300-600 °C NiO + L

V

O O

O

O H

O C - C H 3 O

N i

O O

O

H O

O H 3 C - C

O H 2 O O H 2

Synthesis & Characterizations of Metal Complexes

107

(VI) TGA spectra of Copper(II) complex of 3-acetyl-4-hydroxy-8,10-

dimethylpyrano[3,2-c]chromene-2,5-dione (Sample code-539)

The spectra shows total 53.279 % weight loss up to 800 °C temperature. The

degradation pathway for the complex may be represented as follows.

Cu[LV(H2O)]2 2O 30-120 °C Cu[L

V(H2O)]2 + nH2O

Cu[LV(H2O)]2 120-180 °C Cu[L

V]2 + (H2O)2

Cu[LV]2 180-300 °C Cu[L

V] + L

V

Cu[LV] 300-600 °C CuO + L

V

O O

O

O H

O C - C H 3 O

C u

O O

O

H O

O H 3 C - C

O H 2 O O H 2

Synthesis & Characterizations of Metal Complexes

108

(V) TGA spectra of Iron(II) complex of 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-546)

The spectra shows total 90.068 % weight loss up to 800 °C temperature. The

degradation pathway for the complex may be represented as follows.

Fe[LXI

(H2O)]2 2O 30-120 °C Fe[LXI

(H2O)]2 + nH2O

Fe[LXI

(H2O)]2 120-180 °C Fe[LXI

]2 + (H2O)2

Fe[LXI

]2 180-300 °C Fe[LXI

] + LXI

Fe[LXI

] 300-600 °C FeO + LXI

O O

O

O H

O C - C H 2 C O C H 3 O

F e

O O

O

H O

O H 3 C O C H 2 C - C

O H 2 O O H 2

Synthesis & Characterizations of Metal Complexes

109

(VI) TGA spectra of Cobalt(II) complex of 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-547)

The spectra shows total 83.109 % weight loss up to 800 °C temperature. The

degradation pathway for the complex may be represented as follows.

Co[LXI

(H2O)]2 . nH2O 30-120 °C Co[LXI

(H2O)]2 + nH2O

Co[LXI

(H2O)]2 120-180 °C Co[LXI

]2 + (H2O)2

Co[LXI

]2 180-300 °C Co[LXI

] + LXI

Co[LXI

] 300-600 °C CoO + LXI

O O

O

O H

O

C - C H 2 C O C H 3 O

C o

O O

O

H O

O H 3 C O C H 2 C - C

O H 2 O H 2 O

Synthesis & Characterizations of Metal Complexes

110

(VII) TGA spectra of Nickle(II) complex of 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-548)

The spectra shows total 80.967 % weight loss up to 800 °C temperature. The

degradation pathway for the complex may be represented as follows.

Ni[LXI

(H2O)]2 . nH2O 30-120 °C Ni[LXI

(H2O)]2 + nH2O

Ni[LXI

(H2O)]2 120-180 °C Ni[LXI

]2 + (H2O)2

Ni[LXI

]2 180-300 °C Ni[LXI

] + LXI

Ni[LXI

] 300-600 °C NiO + LXI

O O

O

O H

O C - C H 2 C O C H 3 O

N i

O O

O

H O

O H 3 C O C H 2 C - C

O H 2 O H 2 O

Synthesis & Characterizations of Metal Complexes

111

(VIII) TGA spectra of Copper(II) complex of 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (Sample code-549)

The spectra shows total 87.940 % weight loss up to 800 °C temperature. The

degradation pathway for the complex may be represented as follows.

Cu[LXI

(H2O)]2 2O 30-120 °C Cu[LXI

(H2O)]2 + nH2O

Cu[LXI

(H2O)]2 120-180 °C Cu[LXI

]2 + (H2O)2

Cu[LXI

]2 180-300 °C Cu[LXI

] + LXI

Cu[LXI

] 300-600 °C CuO + LXI

O O

O

O H

O

C - C H 2 C O C H 3 O

C u

O O

O

H O

O

H 3 C O C H 2 C - C

O H 2 O H 2 O

Synthesis & Characterizations of Metal Complexes

112

3.11 CONCLUSION

All the spectral data are in good agreement with the Figure-3.10 (structure-I & II).

In IR spectral data it can a medium intensity bands in the region 476-486 cm-1

shows

bonding of metal with carbonyl oxygen [28]. Lower conductance data in DMF

indicates that all the metal complexes are non-electrolytes (molar conductance < 16

mho cm2mol

-1; 10

-3 M solution) [29]. Thermo gravimetric analysis of representative

complexes shows that metal(II) complexes are stable even at high temperature. TGA

spectra of metal(II) complex of ligand 3-acetyl-4-hydroxy-8,10-dimethylpyrano[3,2-

c]chromene-2,5-dione (LV) and 4-hydroxy-8,10-dimethyl-3-(3-

oxobutanoyl)pyrano[3,2-c]chromene-2,5-dione (LXI

) shows that up to 800°C

temperature, Co[LV(H2O)]2 (sample code- 537) shows minimum weight of 48.704 %

and Fe[LXI

(H2O)]2 (sample code- 546) shows maximum weight loss of 90.068 %. So,

it can be concluded that Fe[LXI

(H2O)]2 has lowest; while Co[LV(H2O)]2 has highest

thermal stability among the complexes under taken for thermo gravimetric analysis.

Synthesis & Characterizations of Metal Complexes

113

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