Strategic Isolation of a Polyoxocation Mimicking Vanadium(V) Oxide Layered-Structure by Stacking of H2V2O84− Anions Bridged by (147-Triazacyclononane)Co(III) Complexes

摘要

An isolation of a vanadium(V) oxide cluster mimicking V2O5 layered structure was achieved formulated as [{Co(tacn)}4V4O12(OH)4]⁴⁺ (>1) (tacn = 1,4,7-triazacyclononane). From the ⁵¹V NMR spectra of the reaction mixtures, we optimized the reaction condition in terms of a molar ratio of VO4³⁻ and [Co(tacn)(H2O)3]³⁺ as well as a pH value. Cluster >1 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 >1, 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 V2O5 bulk material. As far as we know, this is a first example of an isolation of mixed-metal cluster including a unit of V2O5 structure by a stack of two layers of [H2V2O8]⁴⁻, although cubic V₄O₄ cubane-type clusters are well known. The solid sample of compound >1-Cl and >1-Br shows reversible thermochromic behavior accompanied by crystal to amorphous transformation upon hydration-dehydration process.