Ab initio crystal structure of copper(II) hydroxy-terephthalate by synchrotron powder diffraction and magnetic properties

The structure of Cu-2(OH)(2)(C8H4O4) has been determined by ab initio XRPD methods from synchrotron data. The compound crystallizes in P-1 space group, a = 10.1423(4) Angstrom, b = 6.3388(2) Angstrom, alpha = 3.4841(1) Angstrom, alpha = 99.170(2)degrees, beta = 96.567(2)degrees, gamma = 98.760(3)degrees, D-x = 2.497 g cm(-3). The structure has been fully refined by the Rietveld method down to R-p = 0.077 for 9651 observed data points (513 reflections of which 193 are independent). The structure consists of layered hydroxides Cu(OH)(2) intercalated by terephthalate anions, at the interlayer space forming a 3D framework similar to Co(II)-based compound. The apticity of the tp anion and the octahedral coordination of the metal ions are similar in both compounds and can be formulated as M-2(mu(3)-OH)(2)(A(6)-eta(1), eta(2), eta(1), eta(2)-tp) with M = Cu and Co. Although Cu(II)-based structure is very similar to the monoclinic (C2/m) Co(II)-based analogue, the former is completely ordered in contrast with the later which is disordered. The lower symmetry in Cu(II)-based compound due to the Jahn-Teller effects inducing an elongation of the octahedrons CuO6 with four short distances of about 2.0 Angstrom and two long distances Cu-O up to 2.8 Angstrom is also observed to be different from Co(II)-based compound. Whereas the Co(II) derivative exhibits noncollinear antiferromagnetic coupling between the ferrimagnetic hydroxide layers, the magnetic behavior of the copper(II) analogue indicate a ferromagnetic coupling through the terephthalate bridge between ferromagnetic sheets with in-plane interaction J = +5.5 K. (C) 2004 Elsevier SAS. All rights reserved.