Hydrogen bonding in hexamminenickel(II) salts [Ni(NH 3) 6]X 2(X − = Cl −, Br −, I −, NO −2, NO −3, BF −4, ClO −4) — acceptor strength of anions

Abstract

Infrared spectra of [Ni(NH 3) 6]X 2 (X − = Cl −, Br −, I −, NO − 2, NO − 3, BF − 4, ClO − 4) as well as of 5% deuterated samples in the range 400–4000 cm −1 are presented. The main results are that (i) downshift of ν(NH) and temperature evolution of decoupled ν(ND) show that hydrogen bonds occur in hexamminemetal(II) complexes, and (ii) the hydrogen bond strength NH⋯X − is influenced by the hydrogen bond acceptor strength of X −. This does not follow the base strength series of the anions but is mainly influenced by the net chage of the acceptor atoms. Consequently, the following series of hydrogen bond acceptor strengths for NH⋯X − results: Cl − > Br − = I − = NO − 2 > NO − 3 > ClO − 4 > BF − 4.