Strategic Isolation of a Polyoxocation Mimicking Vanadium(V) Oxide Layered-Structure by Stacking of [HVO] Anions Bridged by (1,4,7-Triazacyclononane)Co(III) Complexes.

An isolation of a vanadium(V) oxide cluster mimicking VO layered structure was achieved formulated as [{Co(tacn)}VO(OH)] () (tacn = 1,4,7-triazacyclononane). From the V NMR spectra of the reaction mixtures, we optimized the reaction condition in terms of a molar ratio of VO and [Co(tacn)(HO)] as well as a pH value. Cluster is stable in a wide range of pH values from 1.5 to 8.0, and the presence of multiple hydrogen bondings in the structure is a unique feature. In the X-ray analysis of cluster , the V⋯ V distances are classified into two groups of relatively shorter distances (2.978(1) Å) and longer interactions (3.554(1) Å), and it is a good model of the substructure of VO bulk material. As far as we know, this is a first example of an isolation of mixed-metal cluster including a unit of VO structure by a stack of two layers of [HVO], although cubic VO cubane-type clusters are well known. The solid sample of compound and shows reversible thermochromic behavior accompanied by crystal to amorphous transformation upon hydration-dehydration process.