THE CRYSTAL-CHEMISTRY OF COPPER(II) DIPICOLINATES

The molecular structure of a new copper dipicolinate, Cu(dipic)(H(2)di pic). H2O, and a refinement of the previously reported Cu(dipic)(H(2)d ipic). 3H(2)O are presented. The Jahn-Teller effect, as operative in s ix-coordinated Cu-II surrounded by two planar tridentate ligands, is r esponsible for the presence of a dianion and a neutral acid molecule i n the structure. As opposed to previously reported copper dipicolinate s, water molecules do not coordinate and in the trihydrate dehydration is facile because interstitial 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 dif ferent copper(II) dipicolinates are known; because of the strong tende ncy of this ligand to form tridentate mononuclear complexes, all of th em, except monoclinic Cu(dipic). 2H(2)O, belong to the class of molecu lar solids. In the monoclinic dihydrate, carbonyl O atoms are involved in defining chains that run parallel to [001] planes. Copyright (C) 1 996 Elsevier Science Ltd