Preparation and solid state characterization of some alkylammonium decavanadates. Crystal structure of the hexakis(n-hexylammonium) decavanadate dihydrate

Abstract

This paper deals with the syntheses and solid state characterization of three new n-alkylammonium decavanadates with general formula (BH) 6[V 10O 28] .2H 2O, where B = n-butyl-, n-pentyl-, and n-hexylamine (hereafter abbreviated as BUTVA10, PENTVA10 and HEXVA10, respectively). The compounds have been prepared by dissolving V 2O 5 in an aqueous solution of the respective amine and adjusting the final pH to 6.0 – 6.5. The compounds have been identified by using thermoanalytical, X-ray diffraction and IR techniques. Suitable single crystals were only obtained for the hexakis(n-hexylammonium) decavanadate(V) dihydrate and its crystal structure was determined. The compound crystallizes in the monoclinic space group P2 1 a , M = 1605.5, a = 10.190(5), b = 18.206(4), c = 19.126(4) A ̊ , β = 105.35(3)°, V = 3447(2) A ̊ 3 , Z = 2, F(000) = 1656, μ = 26.75 cm −1, D x = 1.56, D o = 1.57(1) Mg·m −3, and λ( MoKα) = 0.71069 A ̊ . Final refinement led to R = 0.058, and wR = 0.068. The unit cell is made up of decavanadate anions forming layers, n-hexylammonium cations and water molecules occupying the space among them. The distinguishing feature of this compound is its extensive hydrogen bond network which contributes to the structure stabilization. n-Butylammonium decavanadate dihydrate and n-pentylammonium decavanadate dihydrate are isostructural. Space group was determined by X-ray diffraction data. Powder diffraction patterns were indexed for a monoclinic space group P2 1 m unit cell, with parameters for BUTVA10: a = 16.91(2), b = 19.59(1), c = 16.29(2) A ̊ and β = 102.7(1)°, and for PENTVA10: a = 17.18(2), b = 20.57(2), c = 16.30(5) A ̊ , β = 101.7(2)°.