The [Zn(NH3)4]2+ reactions with quinaldinate or pyrazinoate: A ready synthetic route to zinc(II) coordination polymers?

Abstract

The reaction of [Zn(NH3)4]2+ in aqueous ammonia solution with quinaldinic acid (quinoline-2-carboxylic acid) gave a mononuclear heteroleptic ammine/quinaldinate complex with the [Zn(quin)2(NH3)] composition. The introduced secondary ligand adopted the usual N,O-bidentate chelating coordination. In the analogous reaction with pyrazinoic acid (pyrazine-2-carboxylic acid), complete substitution of ammonia with pyrazionate and water was observed. A mixture of two compounds formed: a mononuclear and already known [Zn(pyraz)2(H2O)2] and a novel one-dimensional (1D) coordination polymer [Zn(pyraz)2(H2O)]n. X-ray structure analysis revealed the pyrazinoate ligands in [Zn(pyraz)2(H2O)]n in two binding modes, in a bidentate chelating coordination and in a tridentate bridging coordination. The bridging pyrazinoate has engaged in binding three out of four donors: a carboxylate oxygen and both nitrogen atoms. A detailed presentation of the structure of [Zn(pyraz)2(H2O)]n and its comparison with the structures of related compounds are given below.