The reaction of Mn-2(CO)(7)(mu-S-2) with [CpNi(CO)](2) yielded the paramagnetic new compound Cp2Ni2Mn(CO)(3)(mu(3)-S)(2) (1) and a new hexanuclear metal product Cp2Ni2Mn4(CO)(14)(mu(6)-S-2)(mu(3)-S)(2) (2). Structurally, compound 1 contains two triply bridging sulfido ligands on opposite sides of an open Ni2Mn triangular cluster. EPR and temperature-dependent magnetic susceptibility measurements of 1 show that it contains one unpaired electron. The electronic structure of 1 was determined by Fenske-Hall molecular orbital calculations which show that the unpaired electron occupies a low lying antibonding orbital delocalized unequally across the three metal atoms. The selenium homologue Cp2Ni2Mn(CO)(3)(mu(3)-Se)(2) (3) was obtained from the reaction of a mixture of Mn-2(CO)(10) and [CpNi(CO)](2) with elemental selenium and Me3NO.2H(2)O. It also has one unpaired electron. Compound 1 reacted with elemental sulfur to yield the dinickeldimanganese compound, Cp2Ni2(CO)(6)(mu(4)-S-2)(mu(4)-S-5), 4, which can also be made from the reaction of Mn-2(CO)(7)(mu-S-2) with [CpNi(CO)](2) and sulfur. Compound 4 was converted back to 1 by sulfur abstraction using PPh3. The reaction of Mn-2(CO)(10) with [CpNi(CO)](2) in the presence of thiirane yielded the ethanedithiolato compound CpNiMn(CO)(3)(mu-SCH2CH2S) (5), which was also obtained from the reaction of Mn-4(CO)(15)(mu(3)-S-2)(mu(4)-S-2) with [CpNi-(CO)](2) in the presence of thiirane. Compound 5 reacted with additional quantities of thiirane to yield the new compound CpNiMn(CO)(3)[mu-S(CH2CH2S)(2)], 6, which contains a 3-thiapentanedithiolato ligand that bridges the two metal atoms. Compound 6 was also obtained from the reaction of Mn-2(CO)(10) with [CpNi(CO)](2) and thiirane. The molecular structures of the new compounds 1-6 were established by single-crystal X-ray diffraction analyses.