New 3-D polyoxovanadoborate architectures based on [V12B18O60]16− clusters

Three new 3-D polyoxovanadoborates {[Cu(dien)(H2O)]3V12B18O54(OH)6(H2O)}·4H3O·5.5H2O (1, dien = diethylenetriamine), {[Cd(H2O)2]3V12B18O54(OH)6(H2O)}·4H3O·9.5H2O (2) and {[Na(H2O)3]4Na2V12B18O56(OH)4(H2O)}(H3dien)2 (3) have been hydrothermally synthesized and structurally characterized. Compounds 1–3 contain vanadoborate cluster [V12B18O60] constructed by two hexameric oxovanadate units [V6O9] and one puckered [B18O42] ring via sharing O atoms. The vanadoborate cage [V12B18O60] can present different degrees of protonation, namely [V12B18O60H6]10− for 1 and 2, [V12B18O60H4]12− for 3. The clusters [V12B18O60H6]10− in 1 are connected by complex cations [Cu(dien)(H2O)]2+ into a new 3-D framework via all terminal O atoms of square-pyramidal [VO5] groups, while the clusters [V12B18O60H6]10−/[V12B18O60H4]12− in 2 and 3 are linked with [Cd(H2O)2]2+ groups/the combination of [Na(H2O)3]+ and Na+ ions to give another two types of new 3-D frameworks via O atoms of [BOx] (x = 3, 4) polyhedra, respectively. Magnetic measurements illustrate that compounds 1 and 2 have antiferromagnetic exchange interactions between metal centers. The theoretical band structure of 2 has been also studied.