The syntheses and structural properties of three dinuclear complexes [L3Co(mu(2) - O2P - (Bn)(2))(3)CoL'][L ''] [one ionic L-3 = py(3), L' = py, L '' = ClO4- (1) and two molecular L-3 = py(3), L' = Cl (2) and L-3 = py, mu(2)-NO3-, L' = py (3)] are reported. Complexes feature octahedral Co-II sites bridged by three dibenzyl-phosphinate ligands to a tetrahedrally ligated Co-II site, with the remaining coordination sites occupied by py, nitrato, and Cl ligands. The Co-Co distances are 4.248 angstrom at 291 K and 4.265 angstrom at 100 K for 1 and 4.278 and 4.0313(7) angstrom for 2, and 3, respectively at 100 K. A fit of the low-temperature magnetic susceptibility data was derived for complex 1 with g = 2.25, TIP = 700 x 10(-6) cm(3) mol lambda = -173 cm(-1), kappa = 0.93, v = -3.9, Delta = 630 cm(-1), J = 0.15 cm(-1), and theta = -1.8 resulting in R(chi(M)) = 2.5 x 10(-5) and R(chi T-M) = 5.8 X 10(-5).