Abstract: Nickel(II) is the only common d-8 first row transition metal, and as such its chemistry is filled with examples of square planar complexes.  Cysteine-nickel interactions in proteins, however, are often not well described by these common square planar geometries.  Appropriate electronic environments for nickel(II) allow
this metal to bind cysteine in geometries other than square planar.  This balance also depends on the cysteine donor atoms--different results are observed for cysteine (SR donor) and selenocysteine (SeR donor) versus the oxygen-donor form. These same carefully tuned electronic environments have also allowed a discrete nickel-borohydride complex to be synthesized.  Well-characterized transition metal-borohydride complexes are relevant to catalytic hydroborations, hydrogenations, and possibly metal-methane activation mechanisms; borohydride can be thought of as a more reactive, but isoelectronic, analog of methane.  Ultimately, these separate borohydride and cysteine results may be combined in one synthetic model of the methane-generating bacterial enzyme called methyl coenzyme reductase.