The crystal chemistry of copper(II) dipicolinates

Abstract

The molecular structure of a new copper dipicolinate, Cu(dipic)(H 2dipic)·H 2O, and a refinement of the previously reported Cu(dipic)(H 2dipic)·3H 2O are presented. The Jahn-Teller effect, as operative in six-coordinated Cu II surrounded by two planar tridentate ligands, is responsible for the presence of a dianion and a neutral acid molecule in the structure. As opposed to previously reported copper dipicolinates, water molecules do not coordinate and in the trihydrate dehydration is facile because interstital water finds easy dehydration pathways; the mechanism involves nucleation and fast bidimensional growth. The monohydrate, however, presents tightly bound (through hydrogen bonds) water and no easy dehydration pathways are available; the dehydration mechanism involves fluid-flux nucleation, mediated by fusion. Five different copper(II) dipicolinates are known; because of the strong tendency of this ligand to form tridentate mononuclear complexes, all of them, except monoclinic Cu(dipic)·2H 2O, belong to the class of molecular solids. In the monoclinic dihydrate, carbonyl O atoms are involved in defining chains that run parallel to [001] planes.