AUTHOR=Sugiarto  , Kawamoto Keisuke , Hayashi Yoshihito 

TITLE=Strategic Isolation of a Polyoxocation Mimicking Vanadium(V) Oxide Layered-Structure by Stacking of [H2V2O8]4− Anions Bridged by (1,4,7-Triazacyclononane)Co(III) Complexes

JOURNAL=Frontiers in Chemistry

VOLUME=6

YEAR=2018

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2018.00375

DOI=10.3389/fchem.2018.00375

ISSN=2296-2646

ABSTRACT=<p>An isolation of a vanadium(V) oxide cluster mimicking V<sub>2</sub>O<sub>5</sub> layered structure was achieved formulated as [{Co(tacn)}<sub>4</sub>V<sub>4</sub>O<sub>12</sub>(OH)<sub>4</sub>]<sup>4+</sup> (<bold>1</bold>) (tacn = 1,4,7-triazacyclononane). From the <sup>51</sup>V NMR spectra of the reaction mixtures, we optimized the reaction condition in terms of a molar ratio of VO<sub>4</sub><sup>3−</sup> and [Co(tacn)(H<sub>2</sub>O)<sub>3</sub>]<sup>3+</sup> as well as a pH value. Cluster <bold>1</bold> 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 <bold>1</bold>, 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 V<sub>2</sub>O<sub>5</sub> bulk material. As far as we know, this is a first example of an isolation of mixed-metal cluster including a unit of V<sub>2</sub>O<sub>5</sub> structure by a stack of two layers of [H<sub>2</sub>V<sub>2</sub>O<sub>8</sub>]<sup>4−</sup>, although cubic V<sub>4</sub>O<sub>4</sub> cubane-type clusters are well known. The solid sample of compound <bold>1-Cl</bold> and <bold>1-Br</bold> shows reversible thermochromic behavior accompanied by crystal to amorphous transformation upon hydration-dehydration process.</p>