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Synthesis and characterization of several new pseudotetrahedral arylthiolate complexes [(TpPh,Me)Ni-SAr] (TpPh,Me = hydrotris{3-phenyl-5-methyl-1-pyrazolyl}borate; Ar = Ph, 2,4,6-iPr3C6H2, C6H4-4-Cl, C6H4-4-Me, C6H4-4-OMe) are reported, including X-ray crystal structures of the first two complexes. With prior results, two series of complexes are spanned, [(TpPh,Me)Ni-S-2,4,6-R''3C6H2] (R'' = H, Me, iPr) plus the xylyl analogue [(TpPh,Me)Ni-S-2,6-Me2C6H3], as well as [(TpPh,Me)Ni-S-C6H4-4-Y] (Y = Cl, H, Me, OMe), intended to elucidate steric and/or electronic effects on arylthiolate coordination. In contrast to [(TpMe,Me)-Ni-SAr] analogues that adopt a sawhorse conformation, the ortho-disubstituted complexes show enhanced trigonal and Ni-S-Ar bending, reflecting the size of the 3-pyrazole substituents. Moreover, weakened scorpionate ligation is implied by spectroscopic data. Little spectroscopic effect is observed in the series of para-substituted complexes, suggesting the observed effects are primarily steric in origin. The relatively electron-rich and encumbered complex [(TpPh,Me)Ni-S-2,4,6-iPr3C6H2] behaves uniquely when dissolved in CH3CN, forming a square planar solvent adduct with a bidentate scorpionate ligand, [(κ²-TpPh,Me)Ni(NCMe)(S-2,4,6-iPr3C6H2)]. This adduct was isolated and characterized by X-ray crystallography. Single-point DFT and TD-DFT calculations on a simplified [(κ-Tp)Ni(NCMe)(SPh)] model were used to clarify the electronic spectrum of the adduct, and to elucidate differences between Ni-SAr bonding and spectroscopy between pseudotetrahedral and square planar geometries. [ABSTRACT FROM AUTHOR]