Synthesis, Characterization and Crystal Structure of a Novel Decavanadate Salt, [V0.50(H2O)5]2[H2(V10O28)]·4(H2O)

Abstract

A novel decavanadate salt, [V<inf>0.50</inf>(H<inf>2</inf>O)<inf>5</inf>]<inf>2</inf>[H<inf>2</inf>(V<inf>10</inf>O<inf>28</inf>)]·4(H<inf>2</inf>O), was obtained by the reaction of NH<inf>4</inf>VO<inf>3</inf> with chinhydrone in an acidic medium. The title compound was characterized in the solid and solution phases by FT-IR, single crystal X-ray diffraction, voltammetry, UV-Vis., EPR and NMR measurements. The crystal data of the compound are: H<inf>30</inf>O<inf>42</inf>V<inf>11</inf>, triclinic, Pī, a = 8.4906 (4) Å, b = 10.4236 (5) Å, c = 11.2861 (6) Å, α = 68.490 (4)°, β = 87.251 (4)°, γ = 67.145 (4)°, V = 851.11 (8) Å3, and Z = 1. In the structure, [H<inf>2</inf>(V<inf>10</inf>O<inf>28</inf>)]4- anion is bound via hydrogen bonds to the dimer state of [V<inf>0.50</inf>(H<inf>2</inf>O)<inf>5</inf>]2+ cations and the water molecules. At this dimer moiety, it has been thought that the oxygen atoms of two water molecules form the bridges between two V(IV) center ions. The presence of high spin V(IV) (I = 7/2) in the compound was verified by EPR measurements. In addition, decavanadate unit gave a shoulder at about 400 nm on the UV-Vis. spectrum of the compound. Moreover, at the FT-IR spectrum, the symmetric and asymmetric stretching vibrations of the bridging V–O–V units were observed. On the cyclic voltammogram of the compound, two reduction peaks (V(V)-V(IV) and V(IV)-V(II) reduction steps, respectively) at −1.03 and −1.35 V were observed at the cathodic scan; however, one oxidation peak (V(II)-V(III) oxidation step) at −1.22 V showed at the anodic scan. NMR results also support that the synthesized salt includes the coordinated water molecules and hydroxo groups.