Electrochemically informed synthesis and characterization of salts of the [Pt2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)4]+ lantern complex containing a Pt-Pt bond of order 1/2.

Detailed electrochemical studies in dichloromethane (0.1 M Bu4NPF6) on the oxidation of the half-lantern [Pt2(kappa2As,C-C6H3-5-Me-2-AsPh2)2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)2] (1) and full-lantern [Pt2(mu-kappaAs,kappaC-C6H3-5-Me-2-AsPh2)4] (2) complexes reveal the presence of an exceptionally stable dinuclear Pt cation 2+. Thus, oxidation of 1 occurs on the voltammetric time scale via a ladder-square scheme to give 2+, whereas 2 is directly converted to 2+. Electrochemically informed chemical synthesis enabled the isolation of solid [2+][BF4-] to be achieved. Single-crystal X-ray structural analysis showed that 2+ also has a lantern structure but with a shorter separation between the Pt centers [2.7069(3) A (2+), 2.8955(4) A (2)]. EPR spectra of 2+ provide unequivocal evidence for axial symmetry of the complex and are noteworthy because of an exceptionally large, nearly isotropic hyperfine coupling constant of about 0.1 cm(-1). Spectroscopic data support the conclusion that the unpaired electron in the 2+ cation is distributed equally between the two Pt nuclei and imply that oxidation of 2 to 2+ leads to the establishment of the metal-to-metal hemibond. Results of extended Huckel molecular orbital and density functional calculations on 2 and 2+ lead to the conclusions that s, p, dz2 mixing of orbitals contributes to the large EPR Pt hyperfine coupling and also that the structural adjustments that occur upon removal of an electron from 2 are driven by the metal-metal bonding character present in 2+.