A powerful means of enhancing our understanding of the structures and functions of enzymes that contain nickel-sulfur bonds, such as Ni superoxide dismutase, acetyl-coenzyme A synthase/carbon monoxide dehydrogenase, [NiFe] hydrogenase, and methyl-CoM reductase, involves the investigation of model compounds with similar structural and/or electronic properties. In this study, we have characterized a trans-mu-1,2-disulfido-bridged dinickel(II) species, [{(tmc)Ni}(2)(S-2)(2+) (1, tmc = 1,4,8,11-tetramethy1-1,4,8,11-tetraazacyclotetradecane) by using electronic absorption, magnetic circular dichroism (MCD), and resonance Raman (rR) spectroscopic techniques, as well as density functional theory (OFT) and time-dependent OFT computational methods. Our computational results, validated on the basis of the experimental MCD data and previously reported H-1 NMR spectra, reveal that 1 is best described as containing two antiferromagnetically coupled high-spin centers. A normal coordinate analysis of the rR yibrational data was performed to quantify the core bond strengths, yielding force constants of k(Ni-S) = 2.69 mdyn/angstrom and k(S-S) = 2.40 mdyn/angstrom. These values provide a useful basis for a comparison of metal S/O bonding in 1 and related Ni-2(O-2), Cu-2(O-2), and Cu-2(S-2) dimers. In both the disulfido and the peroxo species, the lower effective nuclear charge of Ni-II as compared to Cu-II results in a decreased covalency, and thus relatively weaker metal S/O bonding interactions in the Ni-2 dimers than in the Cu-2 complexes.