“Scorpionate-like” complexes that are held together by hydrogen bonds: Crystallographic and spectroscopic studies of (3-NH(t-butyl)-5-methyl-pyrazole)nMX2 (M = Zn, Ni, Co, Mn; n = 3, 4; X = Cl, Br)

Abstract

The hydrogen bonding ligand, 3-NH(t-butyl)-5-methyl-pyrazole, forms “scorpionate-like” first row transition metal complexes that are held together by hydrogen bonds rather than covalent bonds. The formulae of these complexes are (LH)nMX2, where n=3, 4; X=Cl, Br; and LH=3-NH(t-butyl)-5-methyl-pyrazole. The amino-substituted pyrazole can hydrogen bond via both the amino group and the pyrazole NH to form intramolecular NH to halide hydrogen bonds. These complexes have been well characterized and show a 3:1 ratio of ligand to metal for zinc and cobalt (1 and 2), and a 4:1 ratio of ligand to metal for manganese and nickel (3 and 4). The hydrogen bonding interactions appear to be stronger for the 3:1 complexes. The crystallographic and spectroscopic studies (EPR and NMR) have shown that these hydrogen-bonding interactions are strong enough to perturb metal halogen bond distances and, with non-hydrogen bonding solvents, the hydrogen bonds appear to hold these complexes together in solution.