Study on the source of magnetic properties of three novel boratopolyoxovanadates via two-dimensional infrared correlation spectroscopy.

Abstract

Three novel polyoxovanadoborates namely [V12B18O46(OH)14(H2O)0.75]·20.5H2O 1, Na2[V12B18O48(OH)12(H2O)0.5]·26.5H2O 2 and Cd0.5{[Na(H2O)2]2[Na(H2O)]2[Na(H2O)3]2V12B18O53(OH)7(H2O)0.5}·11H2O 3 have been hydrothermally synthesized and structurally characterized. The boratopolyoxovanadate cage [V12B18O60] backbones in 1-3 are constructed by the combination of two hexameric oxovanadate units [V6O9] and one puckered [B18O42] ring via sharing O atoms. All three compounds were obtained under alkaline conditions, and the cluster anions were all [V12B18O60]. But the cations were different, it is inferred that the protonation of the three compound cluster ions is different, respectively [V12B18O46(OH)14(H2O)0.75] in 1, [V12B18O48(OH)12(H2O)0.5]2- in 2 and [V12B18O53(OH)7(H2O)0.5]7- in 3. The V oxidation states ratio of VIV to VV were 2:1 confirmed by valence bond calculation and XPS. We studied the magnetic properties of three compounds by two methods: The variable temperature magnetic susceptibility and the 2D IR COS under magnetic perturbation. From the 2D IR COS under magnetic perturbation map, it is showed that all three: (1) the presence of VIV. (2) Certain quasi-aromaticity from B3O3 six-membered ring. (3) The difference of protonation and the charge of the cluster anions. This work enriches the theory of two-dimensional correlation spectroscopy and also provides a new approach to the study of magnetic materials.