33

Chapter 2

2.1 Introduction:

The various experimental techniques used in research work reported in this thesis

have been discussed in this chapter. The theories of each instrument have also been

discussed briefly.

2.2 Materials:

All the salts were purchased from Merck or Loba chemie. The common organic

solvents were purchased from Merck. The glassy carbon electrodes and platinum electrodes

were purchased from CH instrument Inc., USA. Surfactants were purchased from Sigma-

Aldrich. Water used in all the experiments was purified by MilliQ(Millipore) water

purification system.

Table 2.1: Chemicals used with purchase information:

Chemicals used Manufacturer

1. Benzil LOBA CHEMIE

2. Ethylene diamine ,,

3. Sodium methoxide pure ,,

4. L Ascorbic acid ,,

5. Metal salts MERCK OR LOBA CHEMIE

6. Phthalic anhydride MERCK

7. Salicylaldehyde ,,

8. 1- Butanol ,,

9. Ethylene glycol ,,

10. Potassium superoxide ALDRICH

11. Dopamine hydrochloride SIGMA

12. CTAB, TX-100, SDS HIMEDIA

13. NBT HIMEDIA

14. Semicarbazide hydrochloride Sisco Research labortary

34

Chapter 2

2.3 Experimental technique used in the work:

The various electrochemical techniques used to carry out the works reported in this

thesis have been briefly described in the following sections.

2.3.1 Nuclear Magnetic Resonance Spectroscopy (NMR):

Nuclear Magnetic Resonance spectroscopy (NMR) is basically used for

determination of the structure of organic molecules. This technique also finds its use in

quality control and for determining the purity of a sample. Any nuclei having non zero

nuclear magnetic moment value (I) is NMR active. In this work we have reported NMR

spectra of H and 13

C, both of which have I value ½. On application of a magnetic field this

nuclear magnetic moment vectors splits according to their Iz values +1/2 and -1/2 (the

direction of applied magnetic field is considered as z axis). The magnetic nuclei can be

brought into the excited state from the ground state by application of radiation of

appropriate frequency, known as resonance. In practice the magnetic field is changed

gradually keeping the applied radiation fixed. Nuclei having different chemical

environment comes under resonance at different applied magnetic field resulting in

different peaks. Further a peak corresponding to a particular nuclei splits depending on the

nature and number of other nuclei with I ≠ 0 close to it.

The chemical shift of a nucleus, in NMR spectroscopy, is the difference between the

resonance frequency of the nucleus relative to a standard molecule which is quite often

tetramethylsilane (TMS, Si(CH3)4). Chemical shift is reported in ppm and given the symbol

delta (δ).

δ = (ʋ - ʋref) x106 / ʋref

Where ʋ and ʋref are the resonance frequencies of a sample nucleus and the nuclei of TMS.

The chemical shift value is diagnostic of a nucleus in a particular environment [1].

In our works all the 1H NMR and

13C NMR spectra were recorded on a Bruker

35

Chapter 2

Ultrashield 300MHz NMR spectrometer available in our own department. TMS has been

used as internal standard while either CDCl3 or d6-DMSO as solvents depending on the

nature of the sample. Generally two types of NMR instruments exist- continuous wave and

Fourier transform.

2.3.2 Ultraviolet/Visible Spectroscopy:

UV/Vis or electronic spectroscopy is based on the absorption of electromagnetic

radiation by a molecule in the range 200 nm to 900 nm, where the wavelength of 200 nm to

340 nm are referred as ultraviolet region and from 340 nm to 900 nm is the visible region

[2,3]. In organic molecules the absorption, upon irradiation, may be due to the transitions

between various electronic levels such as,

p p* ; n p* etc.

UV/Vis spectroscopy has been employed in this thesis mainly to analyse different

metal complexes where the transition is known as d-d transition. The combined effect of

ligand field and the electron-electron repulsion between electrons in d orbitals generates a

ground state energy level and a number of higher energy states. Selective transition

between ground state and a selection rule allowed higher energy state is possible providing

information about the structure of a particular metal complex [B N Figgis, Ligand field

theory].

In the UV/Vis spectroscopy the Beer-Lambert law is significant which states that

the absorbance of a sample solution is directly proportional to the concentration of the

absorbing species and the path length [4]. Thus for a fixed path length, UV/Vis spectra can

be analyzed to determine the concentration of the absorbing species in the solution. The

Beer-Lambert law is expressed by the following equation,

A=log10(I0/I) = ε.c.l (equation 2.1)

Where A is the measured absorbance, I0 is the intensity of the incident light at a given

36

Chapter 2

wavelength, I is the transmitted intensity, l the path length of the sample which is equal to

the length of the cuvette used to record the spectra which is 1 cm and c is the concentration

of the absorbing species. ε is the proportionality constant known as extinction coefficient

which is characteristic of a particular species. Beer-Lamberts law is best applicable in case

of dilute solutions having absorbance below 1.0.

Hitachi U-3210 UV-visible spectrophotometer and Shimadzu UV-1800

spectrophotometer have been used in our work.

The basic components of a UV/Vis spectrophotometer are the light source, holder

(for the sample), diffraction grating in a monochromator or a prism (to separate the

different wavelengths of light), and a detector. The radiation source is a Tungsten filament

(300-2500 nm), a deuterium arc lamp, which is continuous over the ultraviolet region (190-

400 nm), continuous Xenon arc lamps, (160-2,000 nm or more), light emitting diodes

(LED) for the visible wavelengths. The detector is typically a photomultiplier tube, a

photodiode, a photodiode array or a charge-couple device (CCD). Single photodiode

detectors and photomultiplier tubes are embedded with scanning monochromators, which

filter the light so that only light of a single wavelength can reach the detector at a time. A

spectrophotometer can be either a single beam or a double beam. In a single beam

instrument I0 must be measured by removing the sample, where as in the double beam

instrument, the light split into two beams before it reaches the sample. One beam is used as

the reference, the other beam passes through the sample. The reference beam intensity is

taken as 100% transmission (or zero absorbance), and the measurement displayed is in the

ratio of the two beam intensities. Some double beam instruments have two detectors

(photodiodes), and the sample and reference beam are measured at the same time [5, 6]

Samples for UV/Vis spectrophotometry was used as liquids, although the

absorbance of gases and even of solids can also be done. Samples are typically placed in a

transparent cell, known as cuvette. The cuvettes are typically rectangular in shape,

commonly with an internal width of one cm. and made of high quality fused silica or quartz

glass which is transparent throughout the UV, visible and near infrared regions.

37

Chapter 2

2.3.3 Fourier Transform Infrared Spectroscopy Studies (FTIR):

Fourier transform infrared spectroscopy is one of the most common spectroscopic

techniques used by chemists. It is the measurement of absorption band at different IR

frequencies for a sample positioned in the path of an IR beam. The main goal of FTIR

spectroscopic analysis is the determination of chemical functional groups in a compound.

Different functional groups absorb characteristic frequencies of IR radiations. The IR

region is commonly divided into three sub areas near IR, mid IR, and far IR, having wave

numbers in the electromagnetic spectrum 13,000-4,000 cm–1

, 4,000-200 cm–1

and 200-10

cm–1

respectively. The mid IR regions within the wavelength 400 cm–1

to 4000 cm–1

are

used in the present study [7-11]. The unit cm–1

is commonly used in modern IR. In the

contrast, wavelengths are inversely proportional to frequencies and their associated energy.

Above the absolute zero temperature, all atoms in molecules are in continuous

vibrational mode with respect to each other. When the frequency of a specific vibration

directed on the molecule is equal to the frequency of the IR radiations, absorption takes

place. The major types of molecular vibrations are stretching and bending. The IR

radiations are absorbed and the associated energy is converted into these types of motions.

The absorption produce discrete (quantized) energy levels. However, the individual

vibrational motion is usually accompanied by other rotational motions. All these

combinations lead to the absorption bands which are not discrete lines as commonly

observed in the mid IR region. The features of IR absorption are generally viewed in the

form of a spectrum with wavelengths or wave numbers along the x-axis and absorption

intensity or percent transmittance along the y-axis. Transmittance (T) is the ratio of radiant

power transmitted by the sample (I) to the radiant power incident on the sample (I0) [4, 7,

12]. Absorbance (A) is the logarithm to the base 10 of the reciprocal of the transmittance

(T).

A = log10 (1/ T) = –log10T = –log10 (I /I0) (equation 2.2)

Perkin-Elmer RX1- IR system and Shimadzu IR Affinity-1 spectrometers are used

38

Chapter 2

to analyze the metal complexes.

A FTIR spectrometer consists of three basic components such as radiation source,

monochromator and detector. The common radiation source for the IR spectrometer is an

inert solid heated electrically to 1000-1800° C. Three popular types of sources are Nernst

glower (made of rare-earth oxides), Globar (made of silicon carbide) and Nichrome coil [5,

6]. They can produce different continuous radiations. The monochromator is a device used

to disperse a broad spectrum of radiation and provide a continuous calibrated series of

electromagnetic energy bands of determinable wavelength or frequency ranges. The prisms

or gratings are the dispersive components used in conjunction with variable-slit

mechanisms, mirrors and filters. For example, a grating rotates to focus a narrow band of

frequencies on a mechanical slit. Narrower slits enable the instrument to distinguish better

for the more closely spaced frequencies of radiations, thereby resulting in good resolution.

The wider slits allow more light to reach the detector and provide better system sensitivity.

Most detectors used in dispersive IR spectrometers can be categorized into two classes,

thermal detectors and photon detectors. Thermal detectors include thermocouples,

thermistors and pneumatic devices (Golay detectors). They measure the heating effect

produced by infrared radiation. Several changes of physical property are quantitatively

determined i.e. expansion of a non absorbing gas (Golay detector), electrical resistance

(thermistor) and voltage at junction of dissimilar metals (thermocouple). The photon

detectors rely on the interaction of IR radiation and a semiconductor material in which non

conducting electrons are excited to a conducting state producing small current or voltage.

Thermal detectors provide a linear response over a wide range of frequencies but exhibit

slower response times and lower sensitivities than photon detectors [13, 14, 15].

I The sample is mixed thoroughly with KBr using mortar and then pressed into a

transparent disk at sufficiently high pressure. To minimize band distortion due to scattering

of radiation, the sample should be ground to particles of 2 μm (the low end of the radiation

wavelength) or less in size. The IR spectra produced by the pellet technique often exhibit

bands at 3450 cm–1

and 1640 cm–1

due to absorbed moisture. Mulls are used as alternatives

for pellets and the common mulling agents include mineral oil or Nujol (high boiling

hydrocarbon oil), Fluorolube (a chlorofluorocarbon polymer) and hexachlorobutadiene. To

39

Chapter 2

obtain a full IR spectrum that is free of mulling agent bands, the use of multiple mulls such

as Nujol and Fluorolube are generally required. The sample (1 to 5 mg) is ground with a

mulling agent (1 to 2 drops) to give a two-phase mixture that has a consistency similar to

toothpaste. This mull is pressed between two IR-transmitting plates to form a thin film. In

the work reported in this thesis all the IR spectra were recorded as KBr pallets.

2.3.4 Liquid chromatography–mass spectrometry (LC-MS)

LC-MS is an analytical chemistry technique that combines the physical separation

capabilities of liquid chromatography with the mass analysis capabilities of mass

spectrometry. LC-MS is a powerful technique used for many applications which has very

high sensitivity and selectivity. It is used for determining masses of particles, for

determining the elemental composition of a sample or molecule, and for elucidating the

chemical structures of molecules. MS works by ionizing chemical compounds to generate

charged molecules or molecule fragments and measuring their mass-to-charge ratios [16].

In a typical MS spectrometer a sample is loaded onto the MS instrument which undergoes

vaporization which is then ionized by one of a variety of methods (e.g., by impacting them

with an electron beam), which results in the formation of charged particles (ions). The ions

are separated according to their mass-to-charge ratio in an analyzer by electromagnetic

fields and detected. The technique has both qualitative and quantitative uses like –

identification of unknown compounds, determination of the isotopic composition of

elements in a molecule and determination of the structure of a compound by observing its

fragmentation.

LC-MS / MS Agilent 1260 infinity spectrometer available at SIF, IIT-Guwahati and.

Agilent LCMS triple quad. 6410 series available at Guwahati biotech park,Guwahati are

used for our study.

MS instruments consist of three modules: An ion source, which can convert gas

phase sample molecules into ions (or, in the case of electron spray ionization, move ions

that exist in solution into the gas phase). A mass analyzer, which sorts the ions by their

40

Chapter 2

masses by applying electromagnetic fields. A detector, which measures the value of an

indicator quantity and thus provides data for calculating the abundances of each ion present.

2.3.5 ESI-Mass Spectroscopy:

Mass spectrometry is an analytical technique that can provide both qualitative

(structure) and quantitative (molecular mass or concentration) information on analyte

molecules after their conversion to ions. The technique has both qualitative and quantitative

uses. ESI uses electrical energy to assist the transfer of ions from solution into the gaseous

phase before they are subjected to mass spectrometric analysis. Ionic species in solution can

thus be analysed by ESI-MS with increased sensitivity. Neutral compounds can also be

converted to ionic form in solution or in gaseous phase by protonation or cationisation (e.g.

metal cationisation), and hence can be studied by ESI-MS.

The molecules of interest are first introduced into the ionisation source of the mass

spectrometer, where they are first ionised to acquire positive or negative charges. The ions

then travel through the mass analyser and arrive at different parts of the detector according

to their mass/charge (m/z) ratio. After the ions make contact with the detector, usable

signals are generated and recorded by a computer system. The computer displays the

signals graphically as a mass spectrum showing the relative abundance of the signals

according to their m/z ratio.

The transfer of ionic species from solution into the gas phase by ESI involves three

steps: (1) dispersal of a fine spray of charge droplets, followed by (2) solvent evaporation

and (3) ion ejection from the highly charged droplets tube, which is maintained at a high

voltage (e.g. 2.5 – 6.0 kV) relative to the wall of the surrounding chamber. LCQ Deca,

Thermo Fisher instrument available at TIFR, Mumbai was used in our study.

41

Chapter 2

2.3.6 Conductivity measurements:

The ease of flow of electric current through a body is called its conductance. In

metallic conductors it is caused by the movement of electrons, while in electrolytic

solutions it is caused by ions of electrolyte. The electrolyte conductance is possible through

movement of positive and negative ions, which originate through dissociation of

electrolyte.

Conductance is the reciprocal of resistance and its unit is Mho or Ohm-1

λ= 1/R

Where, λ is the conductance and R is the resistance.

Since a solution is a three-dimensional conductor, the exact resistance will depend

on the spacing (l) and area (A) of the electrodes. The resistance of a solution in such

situation is directly proportional to the distance between the electrodes and inversely

proportional to the electrode surface. Considering the two electrodes having a cross

sectional area of A m2 and separated by l m. The resistance (R) of the electrolyte solution

present between the two electrodes is given by the relation

R∞l

R∞1/A

R= ρ (l/A) (equation 2.3)

Or ρ=RA/l (equation 2.4)

Where ρ (rho) is proportionality constant is called resistivity (formerly called

specific resistance). It is a characteristic property of the material and it is the resistance

offered by a conductor of unit length and unit area of cross section.

Substituting the value of R

42

Chapter 2

Conductance, λ=1/ρ(l/A)=KA/l (equation2.5)

where K (kappa) is reciprocal of specific resistance called as specific conductance or

conductivity. It is measured in Ω-1

m-1

. This quantity may be considered to be the

conductance of a cubic material of edge length unity. Systronics Conductivity Meter 306

was used in our study.

2.3.7 Thermo gravimetric analysis (TGA):

Thermal methods of analysis may be defined as those techniques in which changes

in physical and /or chemical properties of a substance are measured as a function of

temperature. Thermogravimetric analysis determines the change in weight of the sample as

a function of temperature. This analysis is the act of heating a sample gradually to high

enough temperatures so that different components decompose into gas.

We carried out all the thermo gravimetric experiments mentioned in this thesis using

Mettler Toledo TGA/DSC instrument.

The analyzer usually consists of a high-precision balance with a pan (generally

platinum) loaded with the sample. That pan resides in a furnace and is heated or cooled

during the experiment. A different process using a quartz crystal microbalance has been

devised for measuring smaller samples on the order of a microgram (versus milligram with

conventional TGA)[17] The sample is placed in a small electrically heated oven with a

thermocouple to accurately measure the temperature. The atmosphere may be purged with

an inert gas to prevent oxidation or other undesired reactions. A computer is used to control

the instrument.

TGA is a process that utilizes heat and stoichiometry ratios to determine the percent

by mass of a solute. Analysis is carried out by raising the temperature of the sample

gradually and plotting weight (percentage) against temperature.

43

Chapter 2

2.3.8 Electron Paramagnetic Resonance spectroscopy (EPR):

The EPR spectra were recorded either in JEOL JES-FA200 (at IIT-Guwahati) or

Bruker EMX (at TIFR – Mumbai) or Bruker EMX EPR No. – 1444 (X-band 10-12) (at IIT

–Kanpur) spectrophotometer. The magnetic field was applied up to 30 seconds. Quartz

sample tubes of diameter 3 mm was used to record the spectra. DPPH was used to calibrate

the spectra.

To be EPR active the molecule must be paramagnetic that is it must have at least

one unpaired electron. The complexes reported in this thesis are of copper (II) ion having d9

electronic configuration and hence have one unpaired electron. The copper (II) ion has

nuclear magnetic moment value I = 3/2 and hence quadratic splitting of the EPR peak is

expected.

The EPR involves resonant absorption of electromagnetic radiation by electron

spins (s = ½) in which a splitting energy levels are induced by an applied magnetic field. In

the applied magnetic field, an unpaired electron which possesses both the spin and charge,

therefore a magnetic moment can occupy one of two energy levels. The levels are

characterized by a quantum number which has the values of -1/2 or +1/2. The phenomenon

of EPR occurs when the energy of the quantum equals to the difference between the two

energy levels given by the following relation:

∆E=hν =gμβBo (equation 2.6)

Where B0 is the applied magnetic field, ν the frequency of the applied microwave radiation,

h is the Plank’s constant μβ is the magnetic moment of the electron termed as Bohr

magneton. The g is a spectroscopic variable which is the characteristic of the

paramagnetism. When the spins interact with the incident microwave radiation, there is a

net absorption and this is detected as the EPR signal.

44

Chapter 2

2.3.9 Electrochemical Techniques:

In our work we mainly used two electrochemical techniques cyclic voltammetry

(CV) and Square Wave Voltammetry (SWV). All the electrochemical experiments were

performed in CHI 600B electrochemical analyzer (USA).We used a three electrode systems

and a brief introduction of the electrodes are given below.

Working electrode: In general, an electrode provides the interface across which a charge

can be transferred or felt the effects. The working electrode serves as the surface where the

reaction or transfer of charged species take place. The reduction or oxidation of a substance

at the surface of a working electrode at the appropriate applied potential can transport a

material to the other electrode surface for producing flow of current. The selection of a

working electrode material is critical to experiment. The most commonly used working

electrode is made of platinum, gold, carbon and mercury. Among these, platinum is likely

the most suitable metal electrode, due to good electrochemical inertness and ease of

fabrication into many forms. Electrolyte is usually added to the test solution to ensure

sufficient conductivity. The combination of solvent and electrolyte along with specific

working electrode can measure the potential range. In our experiment we mainly used

platinum and carbon electrode.

Reference electrode: The reference electrode should provide a reversible half-reaction

with Nernstian behaviour that may be constant over a period of time and easy to assemble

and maintain. The most commonly used reference electrodes for aqueous solutions are the

calomel electrode and the silver/silver chloride electrode with potential determined by the

reaction given below:

Hg2Cl2(s) + 2e – = 2Hg (l) + 2Cl

–

AgCl(s) + e– = Ag(s) + Cl

–

During our work the silver/silver chloride electrode was used.

Auxiliary electrode: Auxiliary electrode is also known as the counter electrode, can be any

material and serve as good conductor and does not react with the bulk solution. Reactions

occurring at the counter electrode surface are not so important as long as it continues to

45

Chapter 2

conduct current well. To maintain the observed current the counter electrode will often

oxidize or reduce the solvent or bulk electrolyte.

The Potentiostat: The potentiostat is an electronic device which controls the potential of

the working electrode and uses a dc power source to produce a potential which can be

maintained and accurately determined, while allowing small currents to be drawn into the

system without changing the voltage. It is designed to work with a three electrode cell in

such a way that all current flows between the counter and working electrodes, while the

potential of the working electrode is controlled with respect to the reference electrode. The

potentiostat ensures that the working electrode potential is not influenced by the reactions

which take place. The simplest potentiostat has a means of setting the starting potential and

the switching potential, a sweep rate adjustment, and outputs which monitor working

electrode potential and current flow

2.3.9.1 Cyclic Voltammetry(CV):

Cyclic Voltammetry is often the first experiment performed in an electro analytical

study. In particular, it offers a rapid location of redox potentials of the electropositive

species, and convenient evaluation of the effect of medium upon the redox process [18, 19].

A three electrode system has been used in our work namely – working electrode (WE),

reference electrode (RE) and auxiliary electrode (AE). In cyclic voltammetry (CV)

experiment the potential of the working electrode is cycled, with respect to the reference

electrode, between two values using a potentiostate and the corresponding current at each

potential is recorded. This plot of current versus applied potential is known as cyclic

voltammogram.

The electrochemical reactions take place on the surface of the WE. The role of the

AE is to complete the electrochemical circuit with the WE. Fig.2.I shows a typical cyclic

voltammogram for ferrocene in acetonitrile.

46

Chapter 2

Fig. 2.1: Cyclic Voltammogram of a single electron oxidation-reduction

In Fig.2.1, the reduction process occurs from (a) the initial potential to (d) the

switching potential. In this region the potential is scanned negatively to cause a reduction.

The resulting current is called reduction or cathodic current (ipc). The corresponding peak

potential occurs at (c), and is called the reduction or cathodic peak potential (Epc). The Epc

is reached when all of the substrate at the surface of the electrode has been reduced. After

the switching potential has been reached (d), the potential scans positively from (d) to

(g). This causes oxidation to occur and oxidation or anodic current (Ipa) results. The peak

potential at (f) is called the oxidation or anodic peak potential (Epa).

The average of the reduction peak potential (potential corresponding to miximum

47

Chapter 2

ip = 2.69 x 10

5 n

3/2ACD

½ ν

½

current in reduction process) and oxidation peak potential (potential corresponding to

miximum current in oxidation process) is the redox potential also known as mid-point

potential. The redox potential value has been written as E1/2 throughout the thesis. The

magnitude of the difference between the reduction peak potential and oxidation peak

potential should be 0.059 V for one electron transfer redox system while it is 0.030 V for

two electron redox system. For an electrochemical reversible process the ratio of reduction

and oxidation peak current should be approximately 1.0.

The oxidation or reduction peak current in a cyclic voltammogram is given by the

Randles-Sevcik equation (equation2.7):

Where, ip= peak current (ampere).

n = number of electrons transferred

A= electrode surface area (cm2)

C = concentration (mol cm-2

)

D = diffusion coefficient (cm2s

-1), ν = Sweep rate

(Vs-1

)

In our experiment we mainly used this system for qualitative information of the

compound prepared.

2.3.9.2 Square wave Voltammetry (SWV):

In SWV technique the entire potential range is applied as square waves and current

is plotted against the applied potential. A square wave is superimposed on the potential

staircase sweep (Fig.2.2). Oxidation or reduction of species is registered as a peak or trough

in the current signal at the potential at which the species begins to be oxidized or reduced.

The redox potential values could be obtained directly from the voltammogram as shown in

48

Chapter 2

Fig. 2.3 for ferrocene in acetonitrile solution. The current is measured at the end of each

potential change, right before the next, so that the contribution to the current signal from

the capacitive charging current is minimized. The differential current is then plotted as a

function of potential, and the reduction or oxidation of species is measured as a peak or

trough. In the SWV experiments reported in this thesis the applied square wave amplitude

was 25 mV, the frequency was 15 Hz and the potential height for base staircase wave front

was 4 mV.

Fig.2.2: Square wave potential sweep

The peak current in square wave voltammetry is given by:

ip = k n 2

D 2

∆EA Ca (equation 2.8)

Where ip is the peak current, k is a constant, n refers to the number exchanged electrons, D

is the diffusion coefficient of analyte, ΔEA is the pulse amplitude and Ca is the

concentration of the analyte.

49

Chapter 2

Fig.2.3: Square wave voltammogram of Ferrocene in acetonitrile using Platinum working

electrode with Ag-AgCl as reference. The peak position directly gives the redox potential.

2.3.10 Magnetic Susceptibility measurement:

Magnetic materials may be classified as diamagnetic, paramagnetic, or

ferromagnetic on the basis of their susceptibilities. Magnetic susceptibility measurements

were recorded at room temperature by the Gouy method using Cambridge Magnetic

Balance. The balance works on the basis of a stationary sample and moving magnets. The

pairs of magnets are placed at opposite ends of a beam so placing the system in balance.

Introduction of the sample between the poles of one pair of magnets produces a deflection

of the beam that is registered by means of phototransistors. A current is made to pass

through a coil mounted between the poles of the other pair of magnets, producing a force

50

Chapter 2

restoring the system to balance. At the position of equilibrium, the current through the coil

is proportional to the force exerted by the sample, and can be measured as a voltage drop.

The solid sample is tightly packed into weighed sample tube with a suitable length (l) and

noted the sample weight (m). Then the packed sample tube was placed into tube guide of

the balance and noted the reading (R) was noted. The mass susceptibility, χg, is calculated

using:

Where, = the sample length (cm)

m = the sample mass (g)

R = the reading for the tube plus sample

R0 = the empty tube reading

CBal = the balance calibration constant

Then molar susceptibility χm = χg × molecular formula of the complex. The

Molar susceptibility is corrected with diamagnetic contribution. The effective magnetic

moment, μeff, is then calculated using the following expression:

μeff = 2.83 T× χm

Magnetic moments of simple Cu (II) complexes are generally in the range of 1.70-2.20

B.M, regardless of stereochemistry and independent of temperature except at extremely low

temperature.

51

Chapter 2

2.3.11 X-ray Crystallography:

The X-ray data were collected at 293 K with Bruker Smart APEX II (3 circle X-ray

diffractometer). The SMART software was used for data collection, indexing the reflection

and determination of the unit cell parameters. Integration of the collected data was made

using SAINT XPREP software. Multi-scan empirical absorption corrections were applied

to the data using the program SADABS. The structures were solved by direct methods and

refined by full-matrix least-square calculations by using SHELXTL software. All non-

hydrogen atoms were refined in the anisotropic approximation against F2 of all reflections.

The hydrogen atoms attached were located in difference Fourier maps and refined with

isotropic displacement coefficients. The hydrogen atoms were placed in their geometrically

generated positions. Crystal parameters for the compounds are presented in the

experimental section of the respective chapter.

52

Chapter 2

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