A trinuclear Cd3O14 hexaborate and two nickel borates based on molten salt synthesis and precursor synthesis: structure, characterization, and property

In this work, we used different synthetic methods to prepare metal borates. One cadmium borate Cd3[B6O9(OH)2]2.2NO3.4H2O (1), and two nickel borates Ni0.8Mn0.2{B6O7(OH)3[O(CH2)2NH2]3} (2), [Ni(1-MI)6]·[B5O6(OH)4]2·2DMF (3, 1-MI = 1-methylimidazole, DMF= N, N-Dimethylformamide) were successfully prepared. The structures of these three compounds were confirmed by single crystal powder Xray diffraction, element analysis, FTIR, PXRD, and ICP. 1 was prepared by molten salt synthesis. 2 and 3 were prepared by precursor synthesis, which is a synthetic method by using a certain polyanionic cluster as reagent. 1 shows a novel three-dimensional (3D) structure, in which [B6O11(OH)2] units acting as the basic polyanionic cluster form a two-dimensional (2D) anionic structure. In addition, the unexpected Cd3O14 clusters are connected with the 2D structures leading to 3D structure. Crystal structure of 2 is packed by very large neutral Ni0.8Mn0.2{B6O7(OH)3[O(CH2)2NH2]3} oxo-metal-boron clusters. Crystal structure of 3 consists of [B5O6(OH)4]- cluster, DMF molecule, and [Ni(1-MI)6]2+ complex. Notably, 2 was successfully constructed by the same hexaborate cluster as its precursor. However, 3 only contains Ni2+ cations when a neutral NixMn1-x[B6O7(OH)6] cluster was used as an initial reagent, it shows ability to select a certain metal cation during self-assembly process. Moreover, compounds 1, 2, and 3 exhibit different wide band gaps of 3.06 eV (1), 3.95 eV (2), and 4.24 eV (3).