Scorpionato Halide Complexes [(TpPh,Me)Ni-X] [X = Cl, Br, I; TpPh,Me = Hydrotris(3-phenyl-5-methyl-1-pyrazolyl)borate]: Structures, Spectroscopy, and Pyrazole Adducts.

Pseudotetrahedral scorpionato halide complexes [(Tp^Ph,Me)Ni-X] [Tp^Ph,Me = hydrotris(3-phenyl-5-methyl-1-pyrazolyl)borate] were synthesized by metathesis of Tl(Tp^Ph,Me) and NiX₂ (X = Cl, Br, I). Pyrazole adducts [(Tp^Ph,Me)Ni(Hpz^Ph,Me)(X)] (X = Cl, I) were also obtained. [(Tp^Ph,Me)Ni-X] (X = Br, I) are isomorphous with previously reported [(Tp^Ph,Me)Ni-Cl], and a new solvated pseudo-polymorph [(Tp^Ph,Me)Ni-Cl] ·2CH₂Cl₂ was found in this work. Ni-X bond lengths correspond to ionic radii of the halide ions, but some variations in Ni-Cl and Ni-N bond lengths are respectively attributed to bending of the chloride from the ideal threefold HB ···Ni axis and to the size of the 3-pyrazole substituents. Electronic spectra were rationalized by means of time-dependent (TD) DFT calculations on simplified C_{3 v}-symmetric [(Tp)Ni-X] models. Exogenous pyrazole binds to give the pentacoordinate adducts [(Tp^Ph,Me)Ni(Hpz^Ph,Me)(X)] (X = Cl, I). We obtained a crystal structure of the iodide adduct, as well as that of [(Tp^Ph,Me)Ni(Hpz^Ph,Me)(Cl)] ·0.5MeCN, isomorphous with a previously reported aquo monosolvate. A hallmark of adduct formation is an intramolecular N-H ···X hydrogen bond between the added pyrazole and the adjacent halide ligand, thus giving rise to a strong IR absorption band. The stretching frequency correlates to the N(H) ···X separation for the range of known adducts. [ABSTRACT FROM AUTHOR]