Detailed electrochemical studies in dichloromethane (0.1 M BU4NPF6) on the oxidation of the half-lantern [Pt-2-((KAs)-As-2,C -C6H3-5-Me-2-AsPh2)(2)(mu-KAS,KC-C6H3-5-Me-2-AsPh2)(2)] (1) and full-lantern [Pt-2(mu-KAS,KC-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) angstrom (2(+)), 2.8955(4) angstrom (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-tometal hemibond. Results of extended Huckel molecular orbital and density functional calculations on 2 and 2(+) lead to the conclusions that s, p, d2/z 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(+).