KINETIC-STUDY OF THE THERMAL DEHYDRATION OF COPPER(II) DIPICOLINATES - CRYSTAL AND MOLECULAR-STRUCTURE OF CU(II) (PYRIDINE 2,6-DICARBOXYLATO) DIHYDRATED AND TRIHYDRATED

As a basis for the description of dehydration mechanisms, the molecula r structures of two copper(II) dipicolinates, Cu(dipic).2H(2)O (tricli nic) and Cu(dipic).3H(2)O, are presented and compared with those of ot her copper(II) dipicolinates. The kinetics of the isothermal dehydrati on of the monoclinic and triclinic polymorphs of Cu(dipic).2H(2)O were measured. The monoclinic variety dehydrates in a two-step process; a linear cult relationship is found for the first step and a two-dimensi onal diffusion-controlled reaction (D2) law ((1 - alpha) In(1 - alpha) + alpha = kt) for the second. Triclinic Cu(dipic).2H(2)O dehydrates i n a one-step process. The relation between alpha and time is linear at lower temperatures but gradually changes to an Avrami-Erofe'ev (A(2)) model (- 1n(1 - alpha)(1/n) = kt) at higher temperatures. A qualitati ve model based on optical microscopic observations, structural determi nations and thermogravimetric data is proposed. The general relationsh ip between dehydration behavior and structure in this series of compou nds is discussed. (C) 1997 Elsevier Science Ltd. All rights reserved.