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

Abstract

Under hydrothermal conditions, reactions of NaVO 3, 4,4′-bipyridine and metal salts in the presence of Na 2TeO 3 and halide ions produce hybrid materials [ M ( 4 , 4 ′ -bpy ) 2 ] 2 [ V 7 IV V 9 V O 38 X ] · ( 4 , 4 ′ -bpy ) m ( H 2 O ) 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 [ V 8 IV V 7 V O 38 Cl ] · ( H 2 O ) 3 ( 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 [V 16O 38(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 1 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+, [ V 8 IV V 7 V O 36 Cl ] 6 - cluster and H 2O molecules. Magnetic studies prove that there exist ferrimagnetic interactions in 3 and 4.