Influence of protonation on crystal packing and thermal behaviour of tert-butylammonium decavanadates

Two tert-butylammonium decavanadate(V) salts with the formulae (CH₃)₃CNH₃]₆V₁₀O₂₈] · 8H₂O (1) and (CH₃)₃CNH₃]₄H₂V₁₀O₂₈] (2), have been synthesized and their crystal structures have been determined by means of single-crystal X-ray diffraction. The crystal structure of compound 1 is stabilized by electrostatic forces and an extensive network of hydrogen contacts involving anions, cations and water molecules. The anions and cations of this compound are arranged in layers perpendicular to the 010] direction following the sequence, cation-anion-cation. In the crystal structure of compound (2), each dihydrogen decavanadate(V) anion is joined to three adjacent polyanions by means of O(6)---H ··· O(4) hydrogen contacts forming layers parallel to the plane ( 01) and the hydrophobic groups of the cations are disposed in layers parallel to the anionic sheets. The thermal behaviour of both compounds has been studied. Compound 1 is an octahydrate and its thermal decomposition begins at 70°C with the loss of water of crystallization, while compound 2 is anhydrous and is consequently more stable, with decomposition starting at 200°C.