The calculation of the singlet ground-state (SGS) and the lowest-lying triplet-state (LLTS) geometries of [Pt2(μ-P2O5H2)4]4- in the gas phase using density functional theory (DFT) produces 7% Pt−Pt bond shortening in the LLTS as compared to SGS. The transition from the Pt−Pt antibonding HOMO to the bonding LUMO+1 in the gas phase and to the bonding LUMO in water creates a metal−metal σ bond in both excited states. According to the molecular orbital population analysis in water performed using the conductor-like polarizable continuum model (CPCM) and the SGS geometry, the Pt−Pt bond arises from the overlap of the metal p orbitals. The singlet excited-state energy of 27 240 cm-1 in the gas phase is only 40 cm-1 higher than the experimental absorption energy. The first triplet excited-state energy of 22 730 cm-1 in the gas phase and 22 810 cm-1 in water correlates with the experimental phosphorescence excitation energy of 22 100 cm-1. The energy of the LLTS correlates with the experimental phosphorescence emission energy.