Synthesis, platinum-195 nuclear magnetic resonance spectroscopic and extended X-ray absorption fine structure studies on platinum-(II) and -(IV) thioether macrocyclic complexes

Abstract

Reaction of [PtL][PF₆]₂(L =[12]aneS₄= 1,4,7,10-tetrathiacyclododecane, [14]aneS₄= 1,4,8,11-tetrathiacyclotetradecane or [16]aneS₄= 1,5,9,13-tetrathiacyclohexadecane) with Cl₂–CCl₄ or Br₂–CCl₄ in MeCN solution afforded the corresponding platinum(IV) species [PtX₂L][PF₆]₂ in high yield as yellow (X = Cl) or orange (X = Br) solids. These species have been characterised by IR spectroscopy, FAB mass spectrometry and microanalytical data. Platinum-195 NMR spectroscopic studies on the parent platinum(II) complexes and on the platinum(IV) oxidation products confirm S₄ and S₄X₂ donor sets respectively. These studies also indicate that [PtX₂([16]aneS₄)][PF₆]₂ probably exist as trans-dihalides, whereas [PtX₂([12]aneS₄)][PF₆]₂ and [PtX₂([14]aneS₄)][PF₆]₂ are probably cis-dihalides. The crystal structure of [Pt([16]aneS₄)][PF₆]₂·2MeCN shows the Pt^II occupying a crystallographic inversion centre, co-ordinated to a square-planar tetrathia donor set with the free S-based lone pairs adopting the up, up, down, down configuration, Pt–S 2.310(2)Å. Platinum L-III edge EXAFS (extended X-ray absorption fine structure) data have been recorded for these complexes. The Pt–S bond lengths for the platinum(II) complexes compare well with those derived from single-crystal X-ray crystallography, while the Pt–S and Pt–X distances determined from EXAFS studies for the platinum(IV) complexes show that oxidation of Pt^II to Pt^IV typically results in a slight lengthening of the Pt–S bond lengths.