CHAPTER 1
The Early Transition Metals
BY C. D. GARNER
1 Introduction
This chapter is concerned with the inorganic chemistry of the transition elements Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Tc, and Re. The information presented for each element is generally classified as oxygen, halide (including oxyhalide), nitrogen, sulphur (and selenium), carbonyl, and organometallic compounds, according to the area of interest. Adducts will usually be discussed in the section appropriate to the particular parent species. Within each category, the reports concerning a particular oxidation state are grouped together as far as possible.
The shorthand notation employed (in the tables) to summarize the physical properties reported for a particular compound, is explained in Table A; Table B gives the key to the abbreviations used for some organic molecules in this section.
Reviews relevant to some or all of these transition elements are:
Transition-metal oxo-complexes, W. P. Griffith, Co-ordination Chem. Rev., 1970, 5, 459.
Hydroxide ion as a ligand, V. Baran, Co-ordination Chem. Rev., 1971, 6, 65. Stereochemistry of bis-chelate metalfii) complexes, R. H. Holm and M. J. O'Connor, Progr. Inorg. Chem., 1971, 14, 241.
Chemical reactivity of higher fluorides of the transition metals, T. A. O'Donnell, Rev. Pure Appl. Chem. (Australia), 1970, 20, 159.
Reactions of hydrazine with transition-metal complexes, F. Bottomley, Quart. Rev., 1970, 24, 617.
Chemistry of transition-metal carbonyls; synthesis and reactivity, E. W. Abel and F. G. A. Stone, Quart. Rev., 1970, 24, 498.
Organic synthesis by means of metal carbonyls, M. Ryang and S. Tsutsumi, Synthesis, 1971, 55.
Transition metal clusters with π-acid ligands, R. D. Johnston, Adv. Inorg. Chem. Radiochem., 1970, 13, 471.
Theory of bridge bonding and the structure of dinuclear co-ordination compounds, B. Jezowska-Trzebiatowska and W. Wojciechowski, Transition Metal Chem., 1970, 6, 1.
Inorganic electrosynthesis in non-aqueous solvents, B. L. Laube and C. D. Schmulbach, Progr. Inorg. Chem., 1971, 14, 65.
Fast metal-complex reactions, K. Kustin and J. Swinehart, Progr. Inorg. Chem., 1970, 13, 107.
2 Titanium
The chemistry of titanium has been reviewed, as have the organic complexes of lower-valent titanium. Significant developments in Ti-peroxide chemistry have been reported, and of the new compounds, Ti[N(SiMe3)2]3 is perhaps of prime interest since it appears to involve a trigonal (D3h)d1 system. The majority of studies reported have involved Ti–oxygen compounds and these will be reviewed initially.
A. Oxygen Compounds. — Peroxides. Considerable insight into the nature of the well-known orange species formed on addition of TiIV to an acidic solution of H2O2 has been provided. Below pH = 1 the complex formed is probably Ti(O2)(OH),aq+. Above pH = 1 condensation occurs to form various deprotonation products of dinuclear Ti2O,aq2+. The main species, Ti2O5(OH)2-xx(x = 1 — 6), condense to polynuclear cations (or anions), and a precipitate of TiO3(OH2)n (1 < n< 2) is finally formed. The complexes listed in Table 1 were prepared by addition of the appropriate acid to a solution containing TiIV (0.4 mol l-1) and H2O2 (4 mol l-1) followed by neutralization with alkali. These crystalline complex salts allowed crystallographic investigation. The dipicolinate complex is dinuclear and has C2 symmetry. The Ti atoms are co-ordinated in an approximately pentagonal-bipyrimidal arrangement and are bridged by an oxygen atom. In the TiO2 ring, the O — O distance is 1.45(1), Ti — O = 1.872(7) and 1.905(7) Å, and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].
At pH = 3 — 6, Ti, H2O2, and 8-hydroxyquinoline form a 1:1:2 complex (λmax = 435 nm, ε = 8 × 103) which is extracted by CHCl3.
Oxides. Neutron-diffraction studies of the suboxides of Ti indicate that Ti2O, Ti3O, and Ti6O all exhibit ordered arrangements ir\ the octahedral holes of hep Ti. A new phase, TiO1.82, has been identified between Ti5O9 and Ti6O11.
Titanates and Related Systems. The compounds prepared and the physical properties reported are indicated in Table 2. A large number of these compounds are reported to have cubic unit cells. Fourier analysis of the X-ray diffraction patterns of vitreous 2TiO2,K2O and 2TiO2,Cs2O indicates that the TiIV is octahedrally co-ordinated.
Alkoxy-compounds. The structure of the orange–red compound Ti(OPh)4,PhOH, prepared by the addition of PhOH to Ti(OPri)4, has shown that it is a dimer of octahedrally co-ordinated alkoxytitanium molecules. The rates of molecular rearrangement of bis(phenoxy)bis(chelate)TiIV complexes have been studied and found to increase with decreasing pKa of the parent phenol. The activation entropies for the rearrangements are large and negative and have been interpreted in terms of a transition state resembling a tightly-bound ion-pair. The compounds Ti(OR)3(acac) (R = Pri or But) and TiCl3 (acac) have been shown by n.m.r., i.r., and separation studies to be 1:1 mixtures of TiX4 and TiX2(acac)2 (X = OR or Cl), and not to involve any five-co-ordinate Ti species as had previously been reported. Ti(OR)3Cl compounds have been prepared by treating TiCl4 with alcohols. Thus Ti(OOc)3Cl was prepared by adding octanol to TiCl4 in undecane at 100°C [TEXT UNREADABLE IN ORIGINAL SOURCE] heating at 195°C for 2.5 h. When the reaction was carried out at a [TEXT UNREADABLE IN ORIGINAL SOURCE], or when lower alcohols were used, the reaction stopped at [TEXT UNREADABLE IN ORIGINAL SOURCE] complex formation of MeO- with TiIV has been [TEXT UNREADABLE IN ORIGINAL SOURCE] MeOH containing Me4NCl, LiCl, or Li tosylate (µ = 1) by [TEXT UNREADABLE IN ORIGINAL SOURCE]. A reaction sequence (Scheme 1) involving the [TEXT UNREADABLE IN ORIGINAL SOURCE] oxyaminotitanium acylates containing unsaturated acyl groups has been reported. Other alkoxy-titanium compounds are listed in Table 3.
Complexes. A number of TiIII (and VIII, CrIII) crystalline complexes of mono- acidic phosphates and phosphonates have been prepared and characterized by means of analytical, i.r. and electronic spectral, magnetic and X-ray studies. The complexes are insoluble in water and all common organic solvents and do not melt or decompose at temperatures up to 300°C. It is therefore suggested that they are polymeric in nature, probably involving eight-membered phosphate or phosphonato bridges. A 1:1 TiIII: salicylate complex (K = 3·77 l mol-1) has been identified. This complex hydrolyses at pH > 6 to form a monohydroxy complex (K = 1.71 × 103 l mol-1). Four H2O...
