The facile synthesis of a monoderivatized N2S ligand based on the cyclic diamine diazacycloheptane provides a tridentate donor which coordinates nickel(II), yielding a dithiolate bridged nickel dimer with a hinge angle of 135.7 degrees and acute N-Ni-N bite angles of ca. 80 degrees. Dimer splitting occurs on reaction with iodoacetamide, producing an S-alkylated octahedral complex. Cyanide also cleaves the dimer, resulting in a cyanide-bound N2S square planar monomer with two nucleophilic sites, thiolate-S and cyanide-N. Molecular structures of the dimeric cation, [(mmp-dach)(2)Ni-2]Cl-2, the iodoacetamide derivative, [(dtp-dach)Ni(MeCN)(2)]Cl-2, and an S-oxygenate, [(smp-dach)Ni(CN)], are reported.