Electron Transfer Spectra of Some Adducts of Niobium (V), Tantalum (V), Titanium (IV) and Zirconium (IV) Halides with Lewis Bases

Abstract

Swmmavy. The electron transfer spectra 01 adducts of the tide metal halides with a series of ligands (aitriles, dialkylchalcogenides, phosphoryl and thiophosphoryl ligands and phosphincs) have been studied. The effect of halogen substitution on the halogen metal transitions is discussed by comparing thc spectra of the adducts with those of the hexahalometalates. The origin of the two ligand-metal transitions observed in most adducts is discussed and the splitting of the metal d levels in these aImost octahedral adducts is estimated. For each motal halide, the series of adducts with dialkyl chalcogenides show a linear relationship of slope one between the ligand ionisation potentid and the ligand-metal charge transfer cnergy. Tho ligand pptical electronegativities have been estimated.

Electronic Structure of Luminescent d0 Niobium and Tantalum Imido Compounds cis,mer-M(NR)Cl3L2

“…Band III (∼42 500 cm -1 ; 1c ) occurs near the solvent limit in each case, at similar energy to the Ta ← Cl charge-transfer transitions in TaCl 5 L (L = Lewis base, halide). , Band III is observed at lower intensity and occurs at somewhat higher energy than the LMCT absorptions in the complex halides. For comparison, spectra of TaCl 5 (OEt 2 ) in DCE, 1c , and 7 are plotted together in Figure c.…”

“…Spectral Assignments. If we consider the electronic structure of these compounds based on that of TaCl 5 L (L = Lewis base, Cl - ), , a clear bonding picture emerges. In [TaCl 6 ] - , the splitting of t 2g and e g is small, as is the splitting of t 2g upon substituting Me 2 O for a chloride in C 4 v TaCl 5 L .…”

“…If we consider the electronic structure of these compounds based on that of TaCl 5 L (L = Lewis base, Cl - ), , a clear bonding picture emerges. In [TaCl 6 ] - , the splitting of t 2g and e g is small, as is the splitting of t 2g upon substituting Me 2 O for a chloride in C 4 v TaCl 5 L . Intense UV transitions in these species are assigned as Ta ← Cl charge transfer (LMCT), specifically 1 (2t 2g ← 1t 1g , 2t 1u , 1t 2u , and 1t 1u ) in the hexachlorometalates(V).…”

Six- and eight-coordinate thio- and seleno-ether complexes of NbF5and some comparisons with NbCl5 and NbBr5 adducts

“…The solid-state UV/visible spectrum shows the transitions p(R 2 S) → Nb at 26000 and 38400 cm -1 , which disagrees with the reported solution spectrum which quoted only a 38000 cm -1 band. 13 The p(R 2 S) → Nb transitions are similar in energy to those in complexes of the heavier halides, whilst the p(F) → Nb CT bands which are expected in the far-UV region were not observed. In CH 2 Cl 2 solution at 295 K, the 19 F NMR spectrum is a broad singlet (Table 2), indicating a dynamic system, probably reversible thioether ligand dissociation.…”

“…9,10 These, and the Me 2 Se analogues, were also examined by Merbach and coworkers, and solution UV-visible and 1 H NMR spectra reported, although in many cases these were from complexes generated in situ. [11][12][13] Subsequently, detailed 1 H NMR studies revealed that ligand exchange proceeds by an associative mechanism, in contrast to ether analogues, which react by a dissociative mechanism. 14 There is very little information on dithioether complexes, 15 although a small number of thiacrown complexes [(thiacrown)(NbCl 5 ) x ] have been described.…”