Structural and magnetic ordering in the two-dimensional coordination polymer Co(ox)(bpy-d8), (ox = C2O42-, bpy-d8=4,4 '-bipyridine-d8)

Neutron diffraction and magnetic susceptibility studies of the two-dimensio nal coordination polymer Co(ox)(bpy-d8) are presented, where ox = C2O42- an d byp-d8 = 4,4'-bipyridine-d8 (fully deuterated). The neutron powder diffra ction data reveal a second-order crystallographic phase transition at 290 K . Above 290 K, a disordered structure, space group Immm, is observed that i s closely related to the ordered structure previously proposed on the basis of single crystal X-ray diffraction. At low temperatures, the structure is an ordered variant of the high-temperature phase with space group I222. In both phases, the Co ions are linked by the oxalate forming infinite chains that are crosslinked by the bpy ligands. The magnetic susceptibility follows qualitatively a quasi one-dimensional c hain behavior. It exhibits a broad maximum around 35 K, corresponding to a strong antiferromagnetic coupling through the oxalate bridges. A kink at 9 K marks the onset of long-range antiferromagnetic ordering due to much weak er interchain magnetic interactions. The magnetically ordered structure determined from the low-temperature neut ron diffraction data can be described with the propagation vector (1/2, 1/2 , 1/2), i.e. a doubling of the unit cell in each principal direction. It is concluded that a significant antiferromagnetic interaction is mediated thr ough the bpy ligands. although the Co-Co distance along these bridges is 11 .4 Angstrom. (C) 2001 Elsevier Science Ltd. All rights reserved.