The dinuclear gold(I) dithiophosphonate complex, [Au-2(dtp)(2)] (1), where dtp = [S2P(R)(OR')](-) with R = p-C6H4-OCH3; R' = c-C5H9, has been synthesized and its reaction studied with the phosphine ligands PPh3 and Ph2P(CH2)(n)-PPh2 (n = 1-4). Compound 1 contains two gold atoms homobridged by the anionic dithiophosphonate ligand, forming an eight-membered ring complex in a chair form. After the reaction of 1 with diphosphine ligands, the dinuclear open-ring complexes Au-2(dppm)(dtp)(2) (2), Au-2(dppe)(dtp)(2) (3), Au-2(dppp)(dtp)(2) (4), Au-2(dppb)(dtp)(2) (5) were formed (dppm = diphenylphosphinomethane; dppe = diphenylphosphinoethane; dppp = diphenylphosphinopropane; dppb = diphenylphosphinobutane). The reaction with dppm is stoichiometry-dependent. Thus, when 1 reacts with 2 equiv of dppm, the ionic complex [Au-2(dppm)(2)(dtp)]dtp forms. This dtp counterion was exchanged with tetrafluoroborate to yield [Au-2(dppm)(2)(dtp)]BF4, the crystallization of which afforded two interconvertible isomers, 6-yellow and 7-white. Reaction of 1 with PPh3 affords the tetracoordinate mononuclear complex [Au(dtp)(PPh3)(2)] (8). The molecular structures of 1-8 were confirmed by X-ray crystallography and show multiple coordination modes and geometries. The crystal structures of 1 and its reaction products with dppm (2, 6, 7) show short intramolecular Au...Au aurophilic bonding interactions of 2.95-3.10 Angstrom while no intermolecular interactions were discernible. However, reaction products of 1 with longer-chain Ph2P(CH2)(n)PPh2 ligands, n = 2-4, exhibit structures that lack both intra- and intermolecular Au...Au interactions.