Scorpionato halide complexes [(Tp^Ph,Me)Ni-X] [X = Cl, Br, I; Tp^Ph,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_3v-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.