Electronic communication mediated by a PtI-PtI σ-bond

A binuclear complex [Pt-2(dppm)(2)(C equivalent to CFc)(2)] (1) (dppm = bis(diphenylphosphino)methane, Fc = (C5H5FeC5H4)-C-II, ferrocenyl) containing two redox-active ferrocenylacetylides linked by a Pt-I-Pt-I sigma-bond is designed to probe electronic communication through a C equivalent to C-Pt-Pt-C equivalent to C linkage. The X-ray crystal structure of the complex shows a Pt-Pt bond distance of 2.7023(2) A and a Fe-Fe separation of 14.474(2) Angstrom. The cyclic voltammogram (CV) of 1 displays two quasi-reversible one-electron Fc oxidations (DeltaE(p) approximate to 70 mV at 20 mV s(-1), i(pc)/i(pa) approximate to 1) separated by 267 10 mV, and accordingly the equilibrium constant for the comproportionation 1(2+) + 1 <----> 2 1(+) is estimated to be (3.3 +/- 1.5) x 10(4). These suggest considerable electronic communication between the redox centers in the mixed-valence complex 1+. The LTV-vis-NIR absorption spectrum of 1 shows an intervalence-charge-transfer band at 11300 +/- 50 cm(-1) (epsilon(max) = 610 +/- 10 M-1 cm(-1)), and the electronic coupling parameter H-AB is estimated to be 190 +/- 20 cm-1. Addition of d(10) (AuCl)-Cl-I and (AuBr)-Br-I fragments to the Pt-Pt bond gives rise to two A-frame clusters [Pt-2(mu-AuX)(dppm)(2)(C equivalent to CFc)(2)] (X = Cl or Br), whose X-ray crystal structures are composed of isosceles triangles Of Pt2Au. In contrast to 1, electronic communication through the Pt2Au cluster is very weak, as the CVs of the compounds exhibit no splitting of Fc oxidations. Possible reasons for the shutdown of electronic communication are discussed.