Abstract
This paper describes theoretical studies on adducts of Pt 2(PPh 3) 4(μ-S) 2 with T1(I), Pb(II), In(III) and Ga(III). Using one of the Pb compounds as an example, the fundamental principle of competition for interactions (M-ligand vs. MS; MS vs. PtS) is illustrated; in particular, any ligand bound trans to an MS bond will cause the latter to be weakened more than the other MS bond. The polarizable phosphine ligands also play a role in moderating changes in the PtS interactions. The general weakening of the MS bonds upon ligand coordination, which is also demonstrated by binding energies of Pt 2(PPh 3) 4(μ-S) 2 to various heterometal fragments, could explain why Ga, Pb and Tl do not accept additional ligands. In ( PPh 3) 4 Pt 2( μ 2- S) 2 InCl 3, the In atom is square pyramidally coordinated. Calculations indicate strong pπpπ and dπpπ bonding between In and the Cl atom at the apex of the square pyramid, thus accounting for the unusually short InC1 bond length. With regard to the trend of increasing PtSSPt dihedral angle with increasing heterometal size, it is found that in the parent compound (without the heterometal M), the dihedral angle determines the character of the sulfur lone pairs; it is inferred that the “optimal” orientation of the lone pairs for interactions with the heterometal depends on the size of the latter. This result has implications for all binuclear Pt(II) or Pd(II) compounds with bridging sulfur ligand(s).
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