*Article* **Proton Affinity in the Chemistry of Beta-Octamolybdate: HPLC-ICP-AES, NMR and Structural Studies**

**Victoria V. Volchek 1, Nikolay B. Kompankov 1, Maxim N. Sokolov <sup>1</sup> and Pavel A. Abramov 1,2,\***


**Abstract:** The affinity of [β-Mo8O26] <sup>4</sup><sup>−</sup> toward different proton sources has been studied in various conditions. The proposed sites for proton coordination were highlighted with single crystal X-ray diffraction (SCXRD) analysis of (Bu4N)3[β-{Ag(py-NH2)Mo8O26]}] (**1**) and from analysis of reported structures. Structural rearrangement of [β-Mo8O26] <sup>4</sup><sup>−</sup> as a direct response to protonation was studied in solution with 95Mo NMR and HPLC-ICP-AES techniques. A new type of proton transfer reaction between (Bu4N)4[β-Mo8O26] and (Bu4N)4H2[V10O28] in DMSO results in both polyoxometalates transformation into [V2Mo4O19] <sup>4</sup>−, which was confirmed by the 95Mo, 51V NMR and HPLC-ICP-AES techniques. The same type of reaction with [H4SiW12O40] in DMSO leads to metal redistribution with formation of [W2Mo4O19] <sup>2</sup>−.

**Keywords:** proton transfer; octamolybdate; NMR; chromatography; structural analysis
