Inorganic Chemistry of the Transition Elements Volume 1

A Review of the Literature Published Between October 1970 and September 1971

By B. F. G. Johnson

The Royal Society of Chemistry

Copyright © 1972 The Chemical Society
All rights reserved.
ISBN: 978-0-85186-500-3

Contents

Chapter 1 The Early Transition Metals By C. D. Garner,
Chapter 2 Elements of the First Transitional Period: Elements Manganese — Copper By R. Davis,
Chapter 3 The Noble Metals By L. A. P. Kane-Maguire,
Chapter 4 Lanthanides and Actinides By J. A. McCleverty,
Author Index, 393,

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 molecules and at least one ButOH, have been identified in the first co-ordination sphere of TiIII from an e.s.r. study of aqueous TiCl3 containing ButOH. The c.d. of the TiIII–D- (–)-1,2-propylenediaminetetra-acetic acid system exhibits reversible pH dependence, with the 550 nm band inverting in sign as pH is increased. It is concluded that, as a general rule, absolute configurations of metal complexes cannot be deduced from the signs of their c.d. transitions in the d–d spectral region. Also, the tendency to correlate ligand chirality with optical behaviour is questioned.

The instability constants of the yellow TiIII-antipyrine (L) complexes [TiL2(H2O)4]3+ and [TiL3(H2O)3]3+ have been determined (pH = 0.5 — 1.5) as 2.8 × 10-1 and 1.6 × 10-2, respectively. The solution has λmax = 360 nm,ε = 1.34 × 104. Similarly, the stability constants of 5,5- thiodisalicylic acid with TiIII have been reported (log β = 9.18).

Several studies have been concerned with compounds involving TiIV coordinated to oxygen-donor ligands. Tetrakis(hexafluoroisopropoxide)titanium, Ti[CF3CH(O)CF3]4, was prepared by the reaction of Na[CF3CH(O)CF3] (4 mol) in excess CF3CH(OH)CF3 with TiCl4 (1 mol). The moisture-sensitive liquid was characterized by i.r., mass, and 1H and 19F n.m.r. spectra. The i.r. spectrum of TiO(antipyrine)4(ClO4)2 indicates that the ligand is co-ordinated through its carbonyl oxygen. Molecular weight and conductivity data have also been obtained. Other ligands studied include:

(i) N-Cinnamoylphenylhydroxylamine; TiO(C15H12O2N)2,HCl (orange) was formed, which on treatment with H2o afforded Tio(C15H12O2N)2 (yellow).

(ii) N-Benzoylphenylhydroxylamine formed a 2:1 complex with TiIV which could be extracted into benzene.

(iii) Catechol, salicylic acid, disodium l,2-hydroxybenzene-3,5-disulphonate, and 3-carboxy-4-hydroxybenzenesulphonic acid complexes of TiIV have been investigated by potent io metric titration.

(iv) Glycollic 1:2 (pH = 4), lactic 1:1 (pH = 5.3 and 10.3), malic 1:1 (pH = 3.5 and 9.3), and trihydroxyglutaric 1:1 (pH = 4.5) acid TiIV complexes have been studied spectrophotometrically.

(v) 2-Furohydroxamic and cinnamohydroxamic acid chelates with TiIV have been investigated spectrophotometrically and by extraction into organic phases.

Use of salicylfluorone as a competitive ligand allowed the hydrolysis of mononuclear TiIV to be studied spectrophotometrically. Hydrolysis constants have been determined and a diagram constructed showing the distribution of the Ti(OH)(4-n)+n]ITL (n = 0 — 4) species as a function of pH. The stability constants of the TiIV-carboxylic acid complexes of lactic acid, citric acid (= H3L, complex [Ti(OH)2L,HL]3-),2,3,4-trihydroxybenzoic acid (= H2R, complexes [Ti(OH)3H2R]+ and [Ti(OH)3(HR)2]-), H4edta (complexes [TiO(Hedta)]- and [TiO(edta)]2-) and diethylenetriaminepenta-acetic acid (= H5L, complexes [Ti(HL)] and [TiL]-) have been measured. Similarly, the stability constants for the complexes of TiIV with acetylacetone and pyrocatechol and Bu2P(O)CMe(0H)CO2H have been obtained.

Titanium compounds involving simple oxyanions have been studied. The dissociation constant of Ti(C2O4)-2 ions (pK = 9 at 25°C at infinite dilution)has been evaluated spectrophotometrically in HCl. The reports of TiIV-oxyanion compounds are summarized in Table 4.

B. Halogen Compounds. — 19F N.m.r. spectroscopy has been used to study redistribution reactions of TiIV-fluoro-complexes. Spectra obtained at –60°C for TiClxF4-x2THF complexes have shown that whilst halogens are distributed in a random fashion, specific isomers predominate for a particular compound. Exchange processes occur in [Ti(C2O4)3]2- and [TiF6]2- solutions in MeOH. The ligand distributions are almost random, though the amounts of [TiF4(C2O4)]2- and trans– [TiF2(C2O4)2]2- are slightly greater than expected on this basis. This study has also characterized the anions [TiF6-2xBx]2- (B = bidentate ligand, oxalate, malonate, mono- and dimethylmalonate, or monochloroacetate), [TiF5OR]2- (R = Me, Et, Pr, or Bu), and [TiF5O2CR]2- (O2CR = carboxylic acid anion). A 19F n.m.r. study of some diadducts of TiF4 with some N-oxides of pyridine (4-substituted) and quinoline (4- and 6-substituted) has been reported. The chemical shift data have been interpreted in terms of Ti <- F π-bonding. Table 5 summarizes other work reported on TiIV-F compounds.

The i.r. and electronic spectral data for the series of compounds M3[TiF6] [M3 = Na3, K3, (NH4), or K2Na] suggested” a distortion of the [TiF6]3- ion which increases with the cation size. The compound Na2K[TiF6] could not be isolated.

Some interesting studies in fused-salt systems have been reported. Ti(AlCl4)2 has been prepared in several ways, and has been characterized by X-ray and electronic spectral studies; the presence of octahedrally co-ordinated TiII was confirmed. TiAlCl5 was obtained by heating a Ti(AlCl4)2 –AlCl3 (1:5) mixture. Thermodynamic analysis of TiII and TiIII halides dissolved in alkali-metal halides has shown that the systems, which contain anionic Ti complexes, are stable. The heat of formation of the black salt, 9NaCl,2TiCl3,-TiCl2, was also calculated. The compounds KTiCl3, K2TiCl4, and K3Ti2Cl9 have been identified by X-ray diffraction techniques in the TiCl2–TiCl3–KCl system.

The reaction of TiCl4 with PCl5 in POCl3 formed [PCl4][Ti2Cl10] (yellow–orange); however, in SOCl2 [PCl4] [Ti2Cl9] (bright yellow) was obtained. X-Ray crystallography has shown that both compounds contain octahedrally co-ordinated TiIV. The formation of different anions may be due to the different co-ordinating abilities of the solvents.

Reduction by alkali metals in pyridine has been investigated. The new complexes TiCl2,4py and Ti,2py,1.5THF were prepared and characterized by i.r. and electronic spectra and magnetic susceptibility measurements. The former complex (µ = 3.0 BM) is the first magnetically dilute TiII complex reported. The synthesis and thermogravimetric, X-ray, and magnetic properties of the complexes TiCl3,THF (grey), TiCl3,2THF,nC6H6 (n = 0 or 1) (green), and TiC3l,3THF (blue) have been examined. The reaction of the latter with Et2PPEt2 gave an oil (possibly TiCl3,Et2PPEt2). I.r. and electronic spectra for, and the nature of the thermal decomposition products of, trans-[TiCl2- (MeOH)4]Cl and [TiCl(MeOH)5]Cl2 have been reported. TiCl3,MeCN- ,2C2H3CN and TiCl3,C4H8O,C2H3CN have been prepared; the magnetic properties and the absorption spectra indicate the presence of octahedral TiIII, and the i.r. spectra suggest that the acrylonitrile is N-bonded.

(Continues…)Excerpted from Inorganic Chemistry of the Transition Elements Volume 1 by B. F. G. Johnson. Copyright © 1972 The Chemical Society. Excerpted by permission of The Royal Society of Chemistry.
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