Thermal evolution and crystal structures of the 3,5-pyrazole dicarboxylic acid (hydrated form and anhydrous): Ligations with nickel II and barium II

摘要

A crystalline form of anhydrous 3,5-pyrazole dicarboxylic acid (H(3)pdc), H(3)pdc-alpha, which is the most stable form at room temperature, has been identified by a variable temperature diffraction study of the commercial form, H(3)pdc,H2O. Single crystals of H(3)pdc,H2O, anhydrous H(3)pdc-beta, the high temperature form, as well as Ni(Hpdc),4H(2)O and Ba(H(2)pdC)(2)(H(3)pdc)(2) have been prepared, and their crystal structures determined. The structures of H(3)pdc,H2O, and H(3)pdc-beta consist of a planar central pyrazole ring, with two carboxylic groups slightly twisted from coplanarity, due to a complex hydrogen bonding scheme. The alpha form transforms into the P variety upon heating (> 240 degrees C). The mononuclear complex, Ni(Hpdc),4H(2)O, in which deprotonated H(3)pdc serves as a bidentate ligand, has been characterized. The crystal structure of Ba(H(2)pdc)(2)(H(3)Pdc)(2) displays a 50% cationic partial occupancy, with double layers of [Ba-0.5(H(2)pdc)(H(3)pdc)](infinity) planar, polymeric type ribbons along the [010] direction, linked to each other via the Ba coordination scheme along the a axis of the unit cell, with a stacking of Ba(H(2)pdc)(2)(H(3)pdc)(2) layers parallel to (001). (c) 2006 Elsevier B.V. All rights reserved.