Reaction of [(n-Bu)(4)N](2)[Re2Cl8] with the tetrathiafulvalene phosphine ligand o-{P(C6H5}(2))(2)(CH3)(2)TTF (o-P2) in refluxing ethanol produces the mixed-nuclearity salt [ReCl2(o-P2)(2)][Re2Cl6(o-P2)] (1.2), composed of the mononuclear Rem complex (1) and the mixed-valence Ren-Rem dinuclear anion (2). The complex crystallizes as a CH2Cl2 solvate in the triclinic space group P (1) over bar, a = 13.4559(1) Angstrom, b = 20.4015(3) Angstrom, c = 21.5538(1) Angstrom, alpha = 88.261(1)degrees, beta = 72.987(1)degrees, gamma = 84.933(1)degrees and Z = 2. The molecular cation consists of two trans o-P2 ligands in the equatorial plane and axial chloride ligands. The dinuclear anion adopts an eclipsed geometry with an unsymmetrical coordination environment for the two metal atoms; one Re-II center is coordinated to a chelating o-P2 ligand and two chlorides while the other Re atom is coordinated to four chloride ligands. The dinuclear portion of the salt is a monoanion which leads to a formal bond order assignment of 3.5, based on the fact that the molecule possesses an Re-2(5+) core. The salt was further characterized by infrared and electronic spectroscopies, electrochemistry, and variable temperature magnetic susceptibility; the presence of the individual ions in bulk samples was verified by positive and negative FAB mass spectrometry. Isolation of the two separate ions was achieved by treatment of the salt with Co(C5H5)(2), which reduces the Re-III cation to the Re-II complex ReCl2-(o-P2)(2) (3). This neutral compound was separated from the byproduct salt [Co(C5H5)(2)] [Re2Cl6(o-P2)] and reoxidized with CCl4/CH2Cl2 or NOBF4 to produce [ReCl2(o-P2)(2)][Cl] (1 .[Cl]) and [ReCl2(o-P2)(2)][BF4] (1.[BF4]), respectively. Compounds 3, 1 .[Cl], and 1 .[BF4] were identified by a combination of infrared spectroscopy, mass spectrometry, and cyclic voltammetric measurements. Variable temperature de susceptibility studies of [ReCl2(o-P2)(2)][Re2Cl6-(o-P2)] (1 2) revealed classical Curie paramagnetic behavior (with a Curie constant equal to 0.395) and a large temperature independent paramagnetic contribution (chi(TIP) = 9.64 x 10(-3) emu/mol). The EPR spectrum of 1.2 consists of a broad, complex signal due to hyperfine interactions to both isotopes Re-185,Re-187 (I = 5/2) and P-31 (I = 1/2) which is typical for paramagnetic metal-metal bonded dirhenium phosphine compounds.