Synthesis, crystal structure and charge-distribution validation of β-Na(4)Cu(MoO(4))(3) adopting the alluadite structure-type

Single crystals of a new variety of tetra­sodium copper(II) tris­[molybdate(VI)], Na(4)Cu(MoO(4))(3), have been synthesized by solid-state reactions and characterized by single-crystal X-ray diffraction. This alluaudite structure-type is characterized by the presence of infinite layers of composition (Cu/Na)(2)Mo(3)O(14) parallel to the (100) plane, which are linked by MoO(4) tetra­hedra, forming a three-dimensional framework containing two types of hexa­gonal channels in which Na(+) cations reside. The Cu(2+) and Na(2+) cations are located at the same general site with occupancies of 0.5. All atoms are on general positions except for one Mo, two Na (site symmetry 2) and another Na (site symmetry -1) atom. One O atom is split into two separate positions with occupancies of 0.5. The title compound is isotypic with Na(5)Sc(MoO(4))(4) and Na(3)In(2)As(3)O(12). The structure model is supported by bond-valence-sum (BVS) and charge-distribution CHARDI methods. β-Na(4)Cu(MoO(4))(3) is compared and discussed with the K(4)Cu(MoO(4))(3) and α-Na(4)Cu(MoO(4))(3) structures.