Study on the hydrogen bonding of two novel boratopolyoxovanadates supramolecular compounds with [V12B18O60]14− cage by spectroscopy

Abstract

Two novel polyoxovanadoborates with the similar vanadium cage but different number of ligand have been hydrothermally synthesized, namely (enH2)6[V12B18O58(OH)2(H2O)0.5] 12H2O and (enH2)10[V12B18O56(OH)4(H2O)]2 16H2O. The structure of 1 and 2 was determined by single crystal X-ray diffraction. Both compounds are connected to form a supramolecular structure through hydrogen bonding. But the number of free ethylenediamine molecules outside the cage of the two compounds is different, and so is the pilling way stacked by hydrogen bonding. We use two-dimensional infrared correlation spectroscopy (2D IR COS), thermogravimetry (TG), and high temperature infrared (HTIR) to study the effect of hydrogen bonding on the thermal stability for two compounds. From the two-dimensional infrared correlation spectrum, it can be seen that the response peaks of νs(V-Oμ), νas(V-Oμ), νs(V=Ot), νas(V=Ot), νas(Ba–O) and νas(Bb-O) of the two compounds are different, which may be caused by the different connection modes between the weak interaction forces of the two compounds. The analysis results of TG and HTIR curves are consistent with the 2D IR COS. Three characterization methods show that hydrogen bonding can not only increase the initial temperature of organic functional groups and crystal water decomposition, but also greatly affect the temperature at which cluster cages begin to decompose. 2D-IR COS provides an effective new method for studying hydrogen bonding.