Hydrogen-bonded aggregates of protonated decavanadate anions in their tetraalkylammonium salts † ‡

Abstract

Decavanadate anions with various degrees of protonation were crystallized with tetraalkylammonium cations, R4N+, where R represents CH3, C2H5, n-C3H7, or n-C4H9. Structure analyses of seven such crystals reveal that these cations allow decavanadate anions to assemble with each other forming various kinds of hydrogen-bonded aggregates. Four types of assembly patterns have been observed: a diprotonated dimer, ([H2V10O28]4−)2, two kinds of triprotonated dimers, ([H3V10O28]3−)2, and a tetraprotonated polymer, ([H4V10O28]2−)∞. Among these, one of the triprotonated dimers exhibits an unprecedented assembly pattern. The degree of protonation in the solid state tends to increase as the size of the cation becomes larger. Each aggregate shows characteristic IR bands in the region 1000–400 cm−1, from which the assembly patterns are distinguishable. The stabilization energies of the hydrogen-bonded aggregates are approximated well by the sum of the hydrogen-bond and electrostatic energies.