Synthesis and characterisation of chromium and vanadium complexes

Abstract

A range of Cr(Ill), V(IlI) and V(V) complexes have been prepared and analysed via IR, UV-vis, X-Ray crystallography, multinuclear NMR spectroscopy (vanadium(V) species only) and microanalysis. Vanadium(V) complexes with hard and soft ligands have been synthesised including the novel complexes [VOCb(EtSCH2CH2SEt)] and [VOCh(MeSCH2CH2SMe)] in anhydrous CH2Ch. The complexes made during this work are the first extended series of complexes ofvanadium(V) with neutral donor ligands. A series of six-coordinate Cr(Ill) and V(III) species were synthesised involving crown ether, crown thioether and mixed ether/thioether crowns. The complexes [MCh(crown)] (M = Cr or V; crown = l2-crown-4, lS-crown-S, 18-crown-6, [12]aneS4' [lS]aneSs, [9]aneS20, [lS]aneS203, [18]aneS303) were formed by reacting [MCh(thf)3] with rigorously dry crown in anhydrous CH2Ch. Mono-aqua species were also synthesised in the presence of small amounts of water [MCh(H20)(crown)] (M=Cr or V; crown=lS crown-S,18-crown-6). Crystal structures of [CrCh(H20)(l8-crown-6)], [VCh(H20)(lS crown-S)] and [CrCh([lS]aneSs)] have been analysed by X-ray crystallography. The affinity for lS-crown-S and 18-crown-6 to pick up H20 is rationalised due to the strain within the adjacent five-membered chelate rings in the anhydrous K3 -coordinated species. A wider survey showed S-M-S angles in five-membered chelate rings are typically around 82°, where as O-M-O have a substantially more acute angle at around 7S0. The crown ether complexes relieve this strain by switching to ~-coordination with the addition of the H20 ligand. The use of the mixed thia/oxa crowns to probe the M-O vs. M-S binding, showed an overall preference for Cr(Ill) and V(III) to bind to thioether rather than the ether donor atoms, which is in contrast to the expected behaviour stated by HSAB theory. II

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