Hybrid materials based on metal-organic coordination complexes and cage-like polyoxovanadate clusters: Synthesis, characterization and magnetic properties

Under hydrothermal conditions, reactions of NaVO3, 4,4-bipyridine and metal salts in the presence of Na2TeO3 and halide ions produce hybrid materials [M(4,4'-bpy)(2)](2)[(V7V9O38X)-V-IV-O-V] center dot (4,4'-bpy)(m)(H2O)(n) (bpy = bipyridine; M = Ni (1, 2), Co (3), Mn (4); X = F (1), Br (2), Cl (3, 4); m = 1.5 (1, 2, 3), 1 (4); and n = 3 for 1, 3.5 for 2, 2 for 3, 2.5 for 4). The variation of organic ligands can modify the inorganic oxide microstructure, just as the synthesis of [Ni(2,2'-bpy)(3)](3) [(V8V7O38Cl)-V-IV-O-V] center dot (H2O), (5) by using 2,2'-bpy instead of 4,4-bpy. Compounds 1-5 were characterized by elemental analyses, infrared spectroscopy, thermogravimetry, manganometric titration, temperature-dependent magnetic susceptibility measurement and single-crystal X-ray structure analysis. Compounds 1-4 are isostructural with cage-like [V16O38(X)](4-) clusters incorporated into the 3D scaffolding afforded by [M(4,4'-bpy)(2)](n) subunits. There exist left and right-handed helical channels in the 3D cationic framework, filled with disordered 4,4'-bpy molecules. To the best of our knowledge, compounds I and 2 are the first examples of hybrid materials that contain V-16 clusters with F- and Br- ions in the center, respectively. Compound 5 consists of [M(2,2'-bpy)(3)](2+), [(V8V7O36)-V-VI-O-V Cl](6-) cluster and H2O molecules. Magnetic studies prove that there exist ferrimagnetic interactions in 3 and 4. (C) 2006 Elsevier Ltd. All rights reserved.