Inorganic Chemistry B Chapter 22 -...

Dr. Said El-Kurdi 4/15/2015

Dr. Said El-Kurdi 1

Inorganic Chemistry B Inorganic Chemistry B

Chapter 22

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d-Block metal chemistry: the first row metals

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the chemistry of the first member of a triad is distinct from that of the two heavier metals, e.g. Zr and Hf have similar chemistries but that of Ti differs

electronic spectra and magnetic properties of many complexes of the first row metals can often be rationalized using crystal or ligand field theory, but effects of spin– orbit coupling are more important for the heavier metals

complexes of the heavier metal ions show a wider range of coordination numbers than those of their first row congeners


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complexes of the heavier metal ions show a wider range of coordination numbers than those of their first row congeners

trends in oxidation states are not consistent for all members of a triad, e.g. although the maximum oxidation state of Cr, Mo and W is +6, its stability is greater for Mo and W than for Cr

metal–metal bonding is more important for the heavier metals than for those in the first row


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22.4 Group 3: scandium

Scandium normally shows one stable oxidation state in its compounds, Sc(III).

The coordination chemistry of Sc(III) is far more limited than that of the other first row d-block metal ions and is generally restricted to hard donors such as N and O.

Coordination numbers of 6 are favored, e.g. [ScF6]3, [Sc(bpy)3]3+, mer-[ScCl3(OH2)3], mer-[ScCl3(THF)3] and [Sc(acac)3]. [ScF7]4 (pentagonal bipyramid)


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22.5 Group 4: titanium

Titanium does not react with alkalis (cold or hot) and does not dissolve in mineral acids at room temperature. It is attacked by hot HCl, forming Ti(III) and H2, and hot HNO3 oxidizes the metal to hydrous TiO2.

Titanium reacts with most non-metals at elevated temperatures

With H2, it forms ‘TiH2’ but this has a wide nonstoichiometric range, e.g. TiH1.7

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The binary hydrides, carbide , nitride and borides are all inert, high-melting, refractory materials.

In its compounds, Ti exhibits oxidation states of +4 (by far the most stable), +3, +2 and, rarely, 0.

tetrahalide acts as a Lewis acid; TiCl4 is the most important, being used with AlCl3 in Ziegler–Natta catalysts for alkene polymerization

[TiCl4(NMe3)2] and [TiCl4(PEt3)2].


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TiCl3 is readily oxidized, and disproportionates above 750K

Complexes of Ti(III) usually have octahedral structures, e.g. [TiF6]3, [TiCl6]3, [Ti(CN)6]3 , trans-[TiCl4(THF)2], trans-[TiCl4(py)2] , mer-[TiCl3(THF)3], mer-[TiCl3(py)3]

and magnetic moments close to the spin-only values.

The electronic absorption spectrum of [Ti(OH2)6]2+ consists of two bands assigned to ‘d–d’ transitions. Is this consistent with what is predicted from the Orgel diagram shown in Figure 21.20? Comment on your answer.

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22.6 Group 5: vanadium

In many ways, V metal is similar to Ti.

The normal oxidation states of vanadium are +5, +4, +3 and +2; oxidation state (0) occurs in a few compounds with –acceptor ligands, e.g. V(CO)6


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Vanadium(V) oxide is amphoteric


The formation of polyoxometallates is a characteristic of V, Mo, W and, to a lesser extent, Nb, Ta and Cr.

The electronic spectrum of [VCl4(bpy)] shows an asymmetric band: max = 21 300 cm1 with a shoulder at 17 400 cm1. Suggest an explanation for this observation.


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The magnetic moment of a green salt Kn[VF6] is 2.79B at 300 K. With what value of n is this consistent?

22.7 Group 6: chromium

Borides, carbides and nitrides exist in various phases (e.g. CrN, Cr2N, Cr3N, Cr3N2) and are inert materials.

The main oxidation states of chromium are +6, +3 and +2. A few compounds of Cr(V) and Cr(IV) are known, but are unstable with respect to disproportionation. Chromium(0) is stabilized by -acceptor ligands


CrF5 is well established. It is a red, volatile solid (mp 303 K), formed by direct combination of the elements at 570 K. The vapour is yellow and contains distorted trigonal bipyramidal CrF5 molecules. It is a strong oxidizing and fluorinating agent.

Solid CrF4 is dimorphic.

In -CrF4, pairs of edge-sharing CrF6-octahedra assemble into columns through Cr F Cr bridges involving the atoms marked Fa


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In -CrF4, Cr4F20-rings (22.14) are connected through the apical Fa atoms to generate columns, each containing four sub-columns.


In CrBr2, four CrBr distances are 254 pm and two are 300 pm. What is the d electron configuration of the Cr centre? Explain the origin of the difference in bond lengths.

In CrBr2, four CrBr distances are 254 pm and two are 300 pm. What is the d electron configuration of the Cr centre? Explain the origin of the difference in bond lengths.

Anhydrous CrF2, CrCl2 and CrBr2 are made by reacting Cr with HX (X=F, Cl, Br) at >850 K


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Chromium-chromium multiple bonds

Chromium(II) carboxylates are dimers of general formula [Cr2(-O2CR)4] or [Cr2L2(-O2CR)4] and are examples of d-block metal complexes that involve metal–metal multiple

[Cr2(-O2CMe)4]




metal–metal quadruple bond


The Cr atoms are defined to lie on the z axis, and each Cr atom uses four (s, px, py and dx2y2 ) of its nine atomic orbitals to form CrO bonds.

Now allow mixing of the pz and dz2 orbitals to give two hybrid orbitals directed along the z axis.

Each Cr atom has four orbitals available for metal–metal bonding: dxz, dyz, dxy and one pzdz2 hybrid, with the second pzdz2 hybrid being non-bonding and pointing outwards from the CrCr-unit




Each Cr(II) centre provides four electrons for CrCr bond formation and these occupy the Mos to give a 2 4 2

configuration, i.e. a quadruple bond.

The red colour of [Cr2(-O2CMe)4] (max = 520nm, see Table 20.2) and related complexes can be understood in terms of the –* energy gap and a 2 4 1 *1 2 4 2 transition.

The chromium–chromium quadruple bond is typically considered to be strong,


22.8 Group 7: manganese

Metallic Mn is slowly attacked by water and dissolves readily in acids. The finely divided metal is pyrophoric in air

At elevated temperatures, it combines with most non-metals




Manganese exhibits the widest range of oxidation states of any of the first row d-block metals. The lowest states are stabilized by -acceptor ligands

Manganese(VII) chemistry is dominated by the manganate(VII) ion (permanganate). The potassium salt, KMnO4, is a strong oxidizing agent

Values of tet for [MnO4]3, [MnO4]2 and [MnO4] have been estimated from electronic spectroscopic data to be 11 000, 19 000 and 26 000 cm1 respectively. Comment on the observed values

Values of tet for [MnO4]3, [MnO4]2 and [MnO4] have been estimated from electronic spectroscopic data to be 11 000, 19 000 and 26 000 cm1 respectively. Comment on the observed values


Values of eff for K2MnO4 and K3MnO4 are 1.75 and 2.80B (298 K) respectively, while KMnO4 is diamagnetic. Rationalize these observations.

Explain why KMnO4 is intensely colored, whereas KTcO4

and KReO4 are colorless.

Calculate (spin-only) for [Mn(CN)6]2.

Most complexes of Mn(III) are octahedral, high-spin d4

and are Jahn–Teller distorted.

The only well-known low-spin complex of Mn(III) is the dark red K3[Mn(CN)6],




Manganese(II) salts are characteristically very pale pink or colourless. For the d5 Mn2+ ion in an octahedral high-spin complex, ‘d–d’ transitions are both spin- and Laporte forbidden


In order for an electron to have orbital angular momentum,

it must be possible to transform the orbital it occupies into

an entirely equivalent and degenerate orbital by rotation.

The three t2g orbitals can be interconverted by rotations

through 90o and an electron in a t2g orbital has orbital

angular momentum.

In an octahedral complex

The eg orbitals, having different shapes, cannot be

interconverted and so electrons in eg orbitals never have angular momentum

Spin and orbital contributions to the magnetic moment




if all the t2g orbitals are singly occupied, an electron in, say, the dxz orbital cannot be transferred into the dxy or dyz orbital because these already contain an electron having the same spin quantum number as the incoming electron.

in high-spin octahedral, orbital contributions to the magnetic moment are important only for the configurations

t2g1, t2g

2, t2g4eg

2 and t2g5 eg

2. For tetrahedral complexes, it is similarly shown that the

configurations that give rise to an orbital contribution are

e2 t21, e2 t2

2, e4 t24 and e4t2

5.

If all the t2g orbitals are doubly occupied, electron transfer is also impossible.


Explain why orbital contributions to the magnetic moments of [MnF6]2 and [Mn(CN)6]2 are not important

Which of the following will be Jahn–Teller distorted: [MnF6]3 or [Mn(CN)6]3 .




22.9 Group 8: iron

The high-spin d4 configuration of Fe(IV) in [FeO4]4 leads to a Jahn–Teller distortion, reducing the symmetry from Td to approximately D2d


22.10 Group 9: cobalt

[CoF6]2 (d5) is low-spin contrasts with the high-spin nature of [CoF6]3 (d6) and the difference reflects the increase in oct with increasing oxidation state.




22.11 Group 10: nickel

Nickel(II) is far the most important oxidation state for the metal

A range of coordination geometries is observed for nickel(II) complexes with coordination numbers from 4 to 6 being common; octahedral and square planar geometries are most usual.

Magnetic moments of octahedral Ni(II) complexes are usually close to the spin-only value of 2.83 B. In contrast, tetrahedral complexes possess magnetic moments 4 B due to orbital contributions (see Section 21.9), and square planar complexes such as [Ni(CN)4]2 (equation 22.94) are diamagnetic.


The red square planar complex bis(dimethylglyoximato)- nickel(II), [Ni(Hdmg)2], is used for gravimetric determination of nickel

The specificity for Ni2+ arises from the low solubility of [Ni(Hdmg)2], not its high stability constant




22.12 Group 11: copper

copper(II) chemistry, Jahn–Teller distortions are observed as predicted for an octahedral d9 ion, although the degree of distortion varies considerably.


Copper(I) is a soft metal center and tends to interact with soft donor atoms such as S and P, although complex formation with O- and N-donor ligands is well documented.

22.13 Group 12: zinc

the chemistry of Zn is essentially confined to that of Zn(II).

octahedral complexes with -accepting ligands will not be favored for metal centers with d7, d8, d9 or d10 configurations.

Inorganic Chemistry B Chapter 22 -...

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