Synthesis and characterisation of mercaptoimidazole, mercaptopyrimidine and mercaptopyridine complexes of platinum(II) and platinum(III). The crystal and molecular structures of tetra(2-mercaptobenzimidazole)- and tetra(2-mercaptoimidazole)platinum(II) chloride

Abstract

Reaction of K 2[PtCl 4] with 2-mercaptobenzimidazole (HL 2) and 2-mercaptoimidazole (HL 3) in aqueous ethanol afforded the new, crystalline, square-planar platinum(II) complexes [Pt(HL 2) 4]Cl 2 .EtOH ( 4) and [Pt(HL 3) 4]Cl 2 .2H 2O ( 5), the crystal and molecular structures of which are reported. In both complexes the ligands are present in the thione form with coordination taking place through the sulphur atom only. The Pt–S bond lengths are 2.304(4) and 2.312(3) Å in complex ( 4) and 2.314(12) and 2.317(12) Å in complex ( 5). The S–Pt–S bond angles are 90.33(13) and 89.67(13)° in complex ( 4) and 94.46(4) and 85.54(4)° in complex ( 5). Reaction of the ligands 4-hydroxy-2-mercaptopyrimidine (HL 4) and 2-mercaptopyridine (HL 5) with K 2[PtCl 4] gave the new, dimeric platinum(III) complex [Pt 2(L 4) 4Cl 2] ( 6) and [Pt 2(L 5) 4Cl 2]·EtOH ( 7) which is similar to a previously reported complex prepared by a different method. In these complexes the organic ligands are bridging N, S donors, the chlorides are terminally coordinated to each platinum and there is a platinum–platinum bond. The reaction of 4-amino-2-mercaptopyrimidine (HL 6) with K 2[PtCl 4] gave the monomeric platinum(II) complex cis-[Pt(HL 6) 2Cl 2]·2H 2O ( 8) in which each HL 6 ligand is coordinated to the metal ion via the exocyclic amino group. Reaction of 4,6-dihydroxy-2-methylmercaptopyrimidine (HL 7) with K 2[PtCl 4] gave the dimeric platinum(II) complex of formula [Pt 2(L 7) 2(HL 7) 2]Cl 2 ( 9), which is suggested to contain bridging L 7 and HL 7 ligands.