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Inorganic Chemistry of the Transition Elements Volume 6
A Review of the Literature Published Between October 1975 and September 1976
By B. F. G. Johnson The Royal Society of Chemistry
Copyright © 1978 The Chemical Society
All rights reserved.
ISBN: 978-0-85186-550-8
CHAPTER 1
The Early Transition Metals
BY F. L. BOWDEN, P. F. HEVELDT, AND D. J. WATSON
PART I: Titanium, Zirconium, Hafnium, Vanadium, Niobium, and Tantalum
by F. L. Bowden
1 Titanium
Introduction. — Reviews have appeared on the structural, organometallic, and general chemistry of titanium. The organometallic chemistry of titanium is included in a text published this year." A new measurement of the natural abundances of the titanium isotopes gives 47.875285 as the atomic weight of titanium (C = 12).
Titanium compounds containing sulphide and amino-groups have been extracted from plant cells by acetone extraction. The reducing activity of the titanium compounds isolated from cells kept in the dark is higher than that after photosynthesis.
Vapour deposition experiments on titanium have shown that on increasing the rate of titanium deposition at constant argon deposition rate, three new absorptions were observed in the spectrum of the matrix in addition to those due to matrix-isolated atoms. These absorptions have been attributed to the dititanium species for which MO calculations indicate a strong 4s–4s σ-interaction.
Reduction of Cp2TiCl2 with A1 in THF under 1 atm CO is the most efficient, giving the red crystalline Cp2Ti(CO)2 in quantitative yields (cf. 80 % with Na-Hg as reducing agent). The carbonyl can also be obtained from Cp2TiBH4 and CO in the presence of Et3N. Reduction of CpTiCl3 with Mg in the presence of C7H7 gives CpTiC7H7. Derivatives of this compound, ([FORMULA NOT REPRODUCIBLE IN ASCII], or indenyl) and (η7-C7H6C6H5)(η5- C5H5)Ti, have been prepared. Their mass spectra indicate the occurrence of CH or CR migrations affording π-C6H6Ti species. Similar fragmentation patterns in the mass spectrum of the green product from CpTiCl3 or CoTiCl2 and C9H9Li are cited in support of a [FORMULA NOT REPRODUCIBLE IN ASCII] structure.
Hydrolysis of titanocene produces the complex [Cp(C5H4)TiOH]2; X-ray crystallography has established that this has the fulvalene structure (1) characteristic of the titanocene molecule (Vol. 4, FORMULA p. 2) and that the titanium atoms are bridged by the two hydroxy-groups.
Oxidative coupling of the PhC [equivalent to] C fragment occurs in the reaction between PhC [equivalent to] CNa and [FORMULA NOT REPRODUCIBLE IN ASCII] to afford [FORMULA NOT REPRODUCIBLE IN ASCII] (2). The η5-C5H5 analogue of (2) has been obtained directly from (η5-C5H5)2Ti and 1,4-diphenylbuta-1,3-diyne. A purple intermediate found in the oxidative coupling reaction has v(C [equivalent to] C) at ca. 2045 cm-1 and was assigned the σ, π-bridged structure (3).
The electronic configuration of dicyclo-octatetranyltitanium has been derived on the basis of C8v local symmetry for the metal. The overall molecular symmetry is much lower than this with one C8H8 ring symmetrically bound (C8v) and the other one unsymmetrically bound (Cs). Vibrational spectroscopic data indicated the former to be the most firmly bound.
Binary Compounds and Related Systems —Halides and Oxyhalides. The heat capacity of TiF4 has been determined. The peculiar temperature dependence of the magnetic susceptibility of β-TiCl3 is attributed to the presence of two kinds of chain-end site. The kinetics of disproportionation of TiCl3 have been measured over the temperature range 873 — 1373 K.
Molecular force constants for TiCl4 have been calculated from i.r. data on the isotopic species 48TiCl4 and Ti35Cl4 in argon matrices, and 48Ti35Cl4 in the gas phase. MO calculations of the ground state of TiCl4 show that as expected, the higher filled MOs are mainly chlorine 3p in character. A formal metal charge of only 1.0 + indicates a considerable deviation from the simple d° description of the molecule. The energy levels of TiCl4 have been calculated by the CNDO method. The existence of long-lived negatively charged molecular ions in the mass spectra of several titanium compounds including TiCl4, is an indication that these compounds have positive electron affinities.
Oxides. Ti2O3 has been investigated by X-ray spectroscopy and by e.p.r. spectroscopy and magnetic susceptibility measurements; there has been an improved MO calculation of its band structure. A band model has been proposed to account for the origin of the magnetic moment and metallic transition of vanadium-doped Ti2O3. According to e.p.r. measurements the Ti3+ ions in mixed valence phases of the system TinO2n-1 have D2h symmetry; the rhombic field splitting parameters were determined.
Chalcogenides. Vapour pressure measurements on sulphur in equilibrium with TixS2 (1.11 >x > 1.00) at 773 — 973 K have provided thermodynamic data on which to base a preparation of TixS2 crystals with well-defined Ti: S ratios, and in addition have confirmed the existence of stoicheiometric TiS2. This has been confirmed independently by intercalation ratios, electron microscopy, and by measurements of electron transport and magnetic susceptibilities. TiS2 has nearly ideal octahedral co-ordination of the metal in a hexagonal laminar structure with an interlayer S — S distance of 3.462(5) Å. Titanium oxides and oxide-carbon mixtures undergo a two-stage sulphidization with H2S at 773 — 1773 K, affording non-stoicheiometric Ti1.25S2.
The structure of 12R-Ti8S1 2 has been refined to an R index of 2.8%, and the structures of a new poly-type 24R of TiS1.80±0.02 and TiS3 have been determined. n-Butyl-lithium in hexane has been found to be a mild but highly efficient reagent for the intercalation of lithium into layered chalcogenides; reaction with chalco-genides of Group IVB is sufficiently exothermic to cause the hexane to boil. This method avoids the problems of decomposition and partial intercalation experienced with high-temperature methods and also avoids the intercalation of ammonia when solutions of lithium in liquid ammonia are used. Moreover, the limiting stoicheiometry LiMX2 (M = Ti or Zr) can be achieved which represents more lithium than can be intercalated by either of the other methods. The view that intercalation involves electron transfer from the (Bun)- anion and intercalation of the Li+ cation to balance the charge is in keeping with the results of an n.m.r. study of LixTiS2 which indicate the donation of an appreciable fraction of the Li 2s electron to the TiS2 layers, the fraction decreasing as x increases. The reaction between TiS2 an alkali-metal halide and H2S at 1073 — 1273 K affords A0.5TiS2 (A = Li, Na, K, Rb, or Cs), whereas TiS2 and sodium naphthalenide afford a product Na0.8TiS2, with a higher alkali-metal concentration.
Two families of copper titanium sulphides have been prepared; they are: [FORMULA NOT REPRODUCIBLE IN ASCII] and CuxTiS2 (0.7 < x< 1). The corresponding selenides and tellurides of the latter class have also been obtained. In this group, the chalcogen atoms form a c.c.p. array with Ti in the octahedral sites between alternate sulphur sheets and copper in the tetrahedral sites in the remaining vacant layers. The structures and magnetic properties of the mixed sulphides (Cr1-TL[xTix)5S6 and (V1-xTix)5S6 have been investigated.
Carbides. TiC single crystals have been obtained from a mixture of TiCl4 and toluene vapours; they are isostructural with NaCl. The band structure in TiC has been determined by X-ray photoelectron spectroscopy. Hydrogen diffuses into the octahedral holes formed by the close-packed Ti atoms of titanium oxycarbides, but according to i.r. data does not react with the oxygen to form OH groups. A study of TiCy where 0.68 ≤ y ≤ 0.94 showed that during hydrogenation, the C sub-lattice undergoes rearrangement: the carbohydride products are of the form [FORMULA NOT REPRODUCIBLE IN ASCII].
Group V Derivatives. A fibrous titanium nitride has been prepared by spark discharge through a vapour mixture of TiX4 (X = Cl or Br), H2, N2, and an amine ; the effects of temperature and composition of TiCl4–H2–N2 mixtures on the rate of deposition of TiN on a tungsten filament has been examined. Titanium dialkylamides decompose to the nitride in the range 573 — 773 K. Ti0.76N1.10 is isostructural with NaCl. TiN reacts with NiO in the range 1473 — 1773 K to give metallic Ni, titanium oxides, and N2.
Red phosphorus and Ti powder heated at 753 — 823 K for 12 h yield TiP2, which decomposes to TiP above 1073 K; TiP2 can also be obtained from TiP and red phosphorus.
TiSb2 has been prepared and its structure and properties investigated."
Borides and Hydrides. Ti and either B or H3BO3 in a plasma arc gave TiB2. The structural data on a boron-rich titanium boride have been reinterpreted in terms of the occupation of interstitial holes in B12 icosahedra by Ti atoms. The enthalpy of formation of TiB2 has been measured and the kinetics of its oxidation by O2studied.
Spin–lattice relaxation times of H in titanium hydride have been measured as a function of temperature and H concentration. Energy levels of TiH3F and TiH+3 have been calculated by the CNDO method.
Titanium(II). — Standard enthalpies of solution have been determined for the molten systems of TiCl3–TiCl2–NaCl and TiCl3-–iCl2. The system VCl3–TiCl2KCl has been studied by thermoanalytical methods.
Titanium (III). — Halides. A [TiF2]+–H2O2–RH system has been used to generate organic free radicals in aqueous solution; the anomalous kinetic behaviour of radical production in the presence of added H2SO4 was attributed to the formation of a TiIII–SO complex which reacts more rapidly with H2O2 than does uncomplexed TiIII. alkali-metal salts of the TiF-4 ion have been prepared; the heavier members of the series are reported to have layer-type structures like that of TlAlF4.
The Na+ and Ti3+ ions in α-NaTiF4 have octahedral F- co-ordination. The same co-ordination geometry has been assigned to the anions in M12[TiCl5, H2O](M1 = Rb, Cs, NH4, or pyH) on the basis of similarities between the spectroscopic and magnetic properties of the salts and those of the known octahedral TiIII complex (pyH)TiCl6.
TiIII has been detected by e.p.r. spectroscopy in electrochemically reduced solutions of TiCl4, and the standard enthalpies of solution have been determined for the systems TiCl3–NaCl,TiCl3–TiCl2–NaCl, and TiCl3–TiCl2. The system VCl–TiCl3–KCl has been studied by thermoanalytical methods. TiCl3 reacts with alkaline K2HgI4 to form a compound with the stoicheiometry [FORMULA NOT REPRODUCIBLE IN ASCII] which liberates HgI2 when heated.
O- and S-Donor Ligands. In frozen aqueous glass, [Ti(H2O)6]3+ has an axial spin Hamiltonian with g[parallel] = 1.988 ± 0.002, and g[perpendicular to] = 1.892 ± 0.002. The stability constant of TiCl2+ in aqueous HCl for µ = 0 is logeK0 = 1.27 — 1.28 in good agreement with values obtained for CrCl2+ and FeCl2+ . The stability constant of TiSO+4 has also been determined.
Photoreduction of oxalato-TiIV complexes in aqueous oxalic acid gave oxalato-TiIII complexes which catalysed the photosensitized decomposition of oxalic acid to CO2 and CO. Hydrolysis also occurred; in the initial stages of irradiation e.p.r. signals characteristic of oxalate radicals were observed. Photochemical reduction of TiIV compounds in alcohol solution is characterized by phototransfer of an electron followed by removal of H from the alcohol to give RCHOH (R = H or Me) and rearrangement of the first co-ordination sphere to give different TiIII complexes depending on the temperature.
The thermal decomposition of 1,4-dioxan and pyridine complexes of TiCl3 has been investigated. Dichlorotetrakis(propan-2-ol)titanium(III) chloride has an ionic structure; four propan-2-ol molecules and two cis chlorines make up the distorted-octahedral co-ordination sphere of the TiIII in the cation.
The stability order for TiIII complexes with α-hydroxy-acids of glycolate > lactate > mandelate is not the order of base strength of the ligands.
Triethyl or tri-n-butyl thiophosphates react with TiCl3 at high temperatures to give polynuclear dialkoxythiophosphate complexes (TiL3)n; polymerization occurs via — S — P(OR)2 — O — bridging.
N-, NO- and NSO-Donor Ligands. Co-ordination of TiIII with o-phen (L) is stepwise with the formation of [FORMULA NOT REPRODUCIBLE IN ASCII], and [TiL3]3+. According to i.r. evidence, o-hydroxy-4-benzamidothiosemicarbazide (L) binds to TiIII through the phenolic O, thioketone S, and amide N atoms in the complex [TiL2]Cl.
The TiIII complex Ti2(C2O4)3N2H4,6H2O is unusual in being air-stable and in exhibiting an e.p.r. signal at room temperature. Nitrilotriacetic acid forms 1:1 and 2:1 ligand: metal complexes with TiIII in the presence of sulphate ions, but only the 1:1 complexes TiH2A+ and TiH2L with edtaH4 (H4A) and diethylenetriaminepenta-acetic acid (H5L) respectively. Complexes of the form TiCl3LxH2O (L =Schiff base ion, x = 0 — 2) have been obtained from Schiff bases derived from vanillin, salicylaldehyde, benzaldehyde, benzidine, dianisidine, phenylenediamine, ethylenediamine, or propylenediamine. They have room temperature magnetic moments in the range 1.44 — 1.75 BM and behave as 1:1 electrolytes in Me2SO.
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Excerpted from Inorganic Chemistry of the Transition Elements Volume 6 by B. F. G. Johnson. Copyright © 1978 The Chemical Society. Excerpted by permission of The Royal Society of Chemistry.
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