The syntheses of Cp*Ni(PEt3)Me and Cp*Ni(PEt3)Br have been accomplished, starting from the useful starting material Cp*Ni(PEt3)(acac). The X-ray crystal structures of Cp*Ni(PEt3)X (X = Br, O(p-C6H4Me), NH(p-C6H4Me), S(p-C6H4Me), OCH3, Me, CH2Ph, H, PEt3+) have been determined, providing a large sample of similar structures for the analysis of ring distortions as well as a systematic variation of X in order to evaluate the trans influence felt by opposite sides of the cyclopentadienyl ring. Major advances include demonstration that Cp can reduce its electron donation to a metal without "slipping", the rational analysis of cyclopentadienyl distortions, and a well-supported trans-influence series for cyclopentadienylmetal complexes. In sum, d(8) Cp*NiL2 complexes are similar to d(8) NiL4 square-planar complexes in terms of bond lengths, binding geometry, and trans influences.