Balance, uniformity, and asymmetry of the structure of volborthite Cu3(OH)2(V2O7)•2H2O

Four structural models of volborthite Cu(3)(OH)(2)(V(2)O(7))center dot 2H(2)O (a = 10.646(2) angstrom, b = 5.867(1) angstrom, c = 14.432(2) angstrom, beta = 95.19(1), V = 897.7(5) angstrom(3), Z = 4, R/R(w) = 0.038/0.046) calculated in the space groups determined from the systematic absences are compared. Based on the structure balance and the similarity of constituting polyhedra, values of the R factor, and isotropic thermal parameters, the space group Ia is found to be preferable, which is the only possible asymmetric and uniform variant. Hydrogen atoms of OH-groups, oxygen atoms and, partially, hydrogen atoms of water are localized.