Inorganic Chemistry of the Transition Elements Volume 4

A Review of the Literature Published between October 1973 and September 1974

By B. F. G. Johnson

The Royal Society of Chemistry

Copyright © 1976 The Chemical Society
All rights reserved.
ISBN: 978-0-85186-530-0

Contents

Chapter 1 The Early Transition Metals, 1,
Chapter 2 Elements of the First Transition Period, 162,
Chapter 3 The Noble Metals, 329,
Chapter 4 Zinc, Cadmium, and Mercury By J. Howell and M. Hughes, 435,
Chapter 5 Scandium, Yttrium, the Lanthanides, and the Actinides By J. A. McCleverty, 471,
Author Index, 500,

CHAPTER 1

The Early Transition Metals

BY F. L. BOWDEN AND C. D. GARNER

PART I: Titanium, Zirconium, Hafnium, Vanadium, Niobium, and Tantalumby F. L. Bowden

1 Titanium

Introduction. — There have been several reviews of the chemical technology of titanium and its compounds. The organometallic and structural chemistry of titanium reported during 1972 has been reviewed as have some aspects of its synthetic chemistry. According to ab initio calculations the Ti — C bond in TiCO and TiCO+ can be described as a CO non-bonding pair that is shifted slightly onto the Ti and a shift of Ti 3d π-orbitals back onto the CO.

Vibrational assignments have been made for bis(cyclo-octatetraene)titanium. The intensities of the skeletal vibrations indicate that the two C8H8 rings are more electrostatically bonded than in the corresponding Th and U compounds. X-Ray photoelectron spectra of (C5H5)M(C7H7) (M = Ti, V or Cr) show that the oxidation state of the metal increases in the sequence M = Cr

The magnetic behaviour of Cp2Ti+pic- has been discussed in terms of the ligand-field model.

The blue, diamagnetic mono- and di-methyl substituted complexes [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] Ti have been prepared by the reaction of (h5-C5H4R)TiCl3 with PriMgBr in the presence of an excess of C7H7R. They are stable up to 300°C but are decomposed by air and water. Their mass spectra indicate substantial rearrangement involving the transfer of a CH or CCH fragment from the seven- to the five-membered ring leading to ions of dibenzenetitanium derivatives.

The full report of the crystal structure of Cp3Ti has appeared. Diphenylacetylene reacts with CpTi(CO)2 in the cold to give the yellow monoacetylene complex Cp2Ti(CO)PhCPh; the acetylene is readily displaced by CO and the complex is an active catalyst for the hydrogenation of olefins and acetylenes. Under more vigorous reaction conditions the metallocycle (1) is formed.

[FORMULA NOT REPRODUCIBLE IN ASCII] (1)

X-Ray diffraction and chemical studies on [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (2) and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3), and 13C n.m.r. studies of ‘titanocene’ (4) have finally established the structure of this unusual molecule. In (2) the titanium atoms are bridged by a µ-(h5-C5H4–C5H4), fulvalene, ligand and by H and H2AlEt2 ligands, whereas in (3) the bridging ligands include both a fulvalene ligand and an [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] ligand. The chemical relationships between ‘titanocene’, (2), and (3) (4) indicate strongly that ‘titanocene’ has the structure shown and this has been supported by C n.m.r. spectroscopy.

[FORMULA NOT REPRODUCIBLE IN ASCII] (2)

[FORMULA NOT REPRODUCIBLE IN ASCII] (3)

[FORMULA NOT REPRODUCIBLE IN ASCII] (4)

‘Titanocene’ has been used to reduce azo-compounds, ketones, alkynes, and organic halides. Results of deuterium-labelling experiments indicate that the hydrogen in the reduced products is derived from the h5-C5H5 rings of the ‘titanocene’. In view of the dihydride structure of (4) it seems more likely that deuterium labelling of titanocene has produced its deuterium analogue and that reduction occurs via the hydride hydrogens.

E.s.r. evidence has been presented to support the proposal that hydrogen and hydrogen-alkyl complexes are formed by treating Cp2M-AlEt complexes with H2. The involvement of titanocene and related species in the reduction of dinitrogen has been further investigated. Permethyltitanocene undergoes a rapid and reversible reaction with N2 forming C5Me5TiN2TiC5Me5. Solutions of this compound in toluene absorb more nitrogen at low temperatures with an accompanying colour change from dark blue to intense purple-blue. At –80°C the absorbed N2 is entirely retained, even under reduced pressure. The amount of nitrogen released when the low-temperature N2 complex reverts to(C5Me5)2 Ti at room temperature is consistent with the stoicheiometry (C5Me5)2TiN2. Furthermore, the H and C n.m.r. spectra of solutions of the complex below –62°C indicate that it exists in two forms. The 15N n.m.r. spectrum of (C5Me5)2Ti15N15N at –61°C showed two doublets, and a singlet at lower field; the equilibrium (5) [??] (6) was proposed. The doublet structure of the higher-field signals was attributed to 15N–15N coupling [J(15N–15N) = 7 [+ or -] 2 Hz] between the non-equivalent nuclei of (5). The i.r. spectrum provided further evidence for two forms of the complex and showed that the N [equivalent to] N bond orders are affected to similar extents by co-ordination in both complexes.

[FORMULA NOT REPRODUCIBLE IN ASCII] (5)

[FORMULA NOT REPRODUCIBLE IN ASCII] (6)

Binary Compounds and Related Systems. — Halides and Oxyhalides. At 1100 — 1450°C TiCl4 reacts with metallic Ti to give lower Ti chlorides with a Cl :Ti ratio in the gas phase of 2.00 — 2.50. An increase in temperature does not affect the degree of reaction of TiCl4. Reduction of the partial pressure of TiCl4 vapour in the original mixture with Ar reduces the Cl:Ti ratio from 2.60 to 2.00. The fraction of Ti2+ ions in a NaCl melt at a concentration of Ti of 0.83 — 0.4 wt. % and at 950 — 1100°C is close to unity (0.80 — 0.97). The amount of Ti2+ increases with decreasing temperature. At the temperature of the electrolytic processes (850 — 900°Q this value is still lower, as indicated by the isotherms of equilibrium potentials of Ti relative to a Cl comparison electrode as a function of the amount of Ti dissolved in the melt. With an increase in temperature the equilibrium constant of the reaction

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

decreases. For low concentrations of Ti and relatively low temperatures (800 — 900°C) it may be considered that all the Ti dissolved in the melt is in the form of Ti2+. Disproportionation of TiCl3 begins at 550°C in an inert atmosphere and at 660 — 80°C in a TiCl4 atmosphere. At 600°C, 95 — 96% TiCl3 is still present. The equilibrium diagram, electrical conductivity, and density of fused TiCl4 — TiBr4 mixtures indicate almost ideal solution behaviour without appreciable chemical interaction in either the liquid or solid phase. This is at variance with an earlier report. TiCl4 has been investigated as an n.m.r. shift reagent.

Titanium(m) oxychloride has been obtained as a hydrate from the hydrolysis of TiCl2–TiCl3 mixtures in air, and as the anhydrous material from the reaction between TiO2 and TiCl2 at 650 — 700°C. Further heating to 700 — 750°C eliminates unchanged TiCl2 and impurities such as TiCl3. TiOCl free of impurities is stable in air.

An electron diffraction study of TiBr4 and TiI4 has shown them to have regular tetrahedral structures. Pure TiF4 has been obtained in high yield (91%) by treating preoxidized ilmenite with FeF3 at 850°C.

Oxides. Experimental work concerning the equilibrium thermodynamic properties of Ti2O, Ti3O, and Ti6O has been reviewed. Cubic (NaCl type) TiO has been prepared by shock compression of an equimolar mixture of Ti and TiO2. The temperature of the mixture was estimated to reach 3000 K at a pressure of 850 kbar. The TiO prepared by this method had a = 4.179 [+ or -] 0.002 Å for a single compression and 4.177 Å for two successive compressions, and d254 = 4.860 + 0.005 g cm-3. Variations in the composition of the initial mixture led to the formation of non- stoicheiometric oxides TiOx, e.g.

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

The electronic structure of titanium monoxide has been studied by X-ray spectroscopy and ESC A. The dissociation constant and heat capacity of TiO at 3000 — 10 000 K have been reported as Kp = 7.77 × 10-6 — 3.39 × 103 atm and Cp = 9.65 — 11.81 cal mol-1 K-1. Analyses of the rotational spectra of the TiO molecule have been carried out.

A comparison of the intensities of the M — O absorption band for TiO1+x and V0 shows the former to diminish more rapidly with increasing x; this effect has been ascribed to the lower degree of polarity in the Ti — O bond. The same explanation has been offered to account for the presence of a deformation absorption in the spectra of TiO, Ti2O3, and TiO2. This absorption band is absent from the spectra of HfO2 and ZrO2. The magnetic susceptibilities and the e.p.r. and optical spectral parameters of TixOy (x = 3 — 10; y = 5,7,9,11,13,15,17 or 19) have been interpreted in terms of the presence of non-interacting, localized Ti3+ ions. These range from ca. 0.01% of the total Ti3+ in Ti3O5 to ca. 40% of the total in Ti10O19. The remaining Ti3+ ions are thought to be involved in homopolar bonds within specific groups of Ti3+ ions.

Ti2O3 and (Ti0.900V0.100)2O3 have been shown to be isostructural with Al2O3, having rhombohedral unit cells with dimensions Ti2O3, a = 5.4325(8) Å, α = 56.75 (1)°, (Ti0.900V0.100)2O3, a = 5.4692(8) Å, α = 55.63(1)°. The effect of substitution by V3+ is to increase the metal-metal distance across shared octahedral faces from 2.579 Å in Ti2O3 to 2.658 Å in the Ti — V compound while decreasing the metal-metal distance across the shared octahedral edge from 2.997 Å to 2.968 Å.

TiO2 has been prepared by the injection of compressed air into molten TiBr4 and by the vapour-phase hydrolysis of TiCl4. A thermodynamic analysis of the latter system indicated that the formation of Ti2O3 and Ti3O5 byproducts is favoured at higher temperatures. Reduction of the titanium oxides TixO (x = 19, 6, 5, 4, 3 or 2) with hydrogen at 600°C, 100 kg cm-2 over 48 h gave mixtures of Ti2O and TiH2. No reaction was observed with TiO or TiO2. TiO2 has the maximum stability towards hydrogen.

Chalcogenides. The crystal structures of titanium sulphides have been reviewed. Ti3S8 has several structural features in common with TiS2 including trigonal-prismatic co-ordination polyhedra about S atoms and cubic co-ordination polyhedra about Ti atoms. Whereas six cube faces are shared with trigonal prisms in TiS2 only, three are shared in Ti3S8. Carbon disulphide has been used as a sulphurizing agent in the preparation of Ti3S4. A material Ti1.2S2 resembling Ti3S4 in its X-ray powder diffraction pattern has been obtained from TiO2 carbon mixtures and H2S. Intermediate oxygen-containing sulphides are formed and these must be mixed with more carbon and reheated to remove all the oxygen.

There is some conflict concerning the electronic nature of TiS2. A band gap between the highest occupied and lowest unoccupied orbitals of ca. 1 eV has been widely accepted. However, an MO energy level diagram derived on the basis of octahedral symmetry for TiS2 from X-ray band spectra showed no evidence of a gap wider than 0.1 eV, the limit of error; that is, TiS2 is a metal or semi-metal rather than a small-gap semiconductor. A similar conclusion was drawn from X-ray photoelectron data on TiS2. Both these results are very different from the 2.0 — 2.7 eV gap derived from optical studies of TiS2. MxTiS2 phases (M = Li, Na, or K; x = 0.3 — 0.5) have been prepared by the reaction of TiS2 with alkali-metal halide melts in an H2S–CS2 atmosphere. The structures of these compounds consist of alkali-metal cations located between negatively charged (TiS2)x– layers of the CdI2 type. They form hydrates with water, the interlayer distances depending on the radius of the alkali-metal cation and on the ambient water-vapour pressure. Water can be replaced partially or totally by polar molecules, which solvate the titanium sulphide layers and the alkali-metal cations. The cations can be replaced by NH+4, Ca2+, and R4N+ ions. Single crystals of FeTiX4 grown by isothermal vapour growth exhibit metallic behaviour. Lattice parameters have been determined for some ternary titanium-containing chalcogenides: [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. Layer intercalation compounds of TiS2 with a variety of amines have been prepared. The limiting composition [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] for n = 4 — 10 and x = 1.05 for n ≥ 16) was established for n-alkylamine adducts which were obtained by displacement of N2H4 from the adduct TiS2,N2H4. The guest molecules are arranged in bimolecular layers between layers of the host lattice. With substituted imidazoles as guest molecules no increase in interlayer spacing occurs on substitution of H by CH3 on nitrogen, while CH3 substitution on C-2 causes an increase of ca. 4 Å. At low values of n (3 — 6), both alkyl chains of the secondary amines [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] are parallel to the TiS2 layers, but the angle of inclination of the longitudinal axis of the alkyl chain towards the layers increases sharply at higher n values.

Carbides, Silicides, and Germanides. Single crystals of TiC were obtained from the reaction

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

in a flow system. Below 1200°C TiC condensed as a polycrystalline film; octahedral crystals formed above 1600°C. The titanium–carbon phase diagram has been analysed by a statistical thermodynamic method. Within the homogeneity region, titanium carbide acquired two crystal structures: (i) a NaCl-type structure, at carbon concentrations > 40 atom % and (ii) a structure belonging to the space group Fd3m at carbon concentrations <40 atom %. Titanium silicides are included in a review of the electronic structures of metal silicides. The enthalpy and heat capacity of TiS2 have been reported, as have the heats of formation of TiSi, Ti5Si3, and TiSi2. TiS2 resists oxidation owing to the formation of thin protective films of oxides and silicate glasses; at 500°C the layer contains α-quartz and TiO2, at 700°C anatase, and at higher temperatures still, rutile containing traces of metallic titanium. The resistance of titanium germanides to oxygen decreases in the series TiGe > TiGe2 > Ti5Ge3; metal oxides and GeO2 are the reaction products.

(Continues…)Excerpted from Inorganic Chemistry of the Transition Elements Volume 4 by B. F. G. Johnson. Copyright © 1976 The Chemical Society. Excerpted by permission of The Royal Society of Chemistry.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.