Synthesis, platinum-195 nuclear magnetic resonance spectroscopic and extended X-ray absorption fine structure studies on platinum-(<scp>II</scp>) and -(<scp>IV</scp>) 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 PtII 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 PtII to PtIV typically results in a slight lengthening of the Pt–S bond lengths.