A Sb-containing Anderson-based polyoxomolybdate cluster, [(CH3)4N]4H8[Na5Sb3(Sb2Mo12O57)]·17H2O [
The crystal structures of the title compounds, which were synthesized at temperatures between 500 and 850 °C via reaction of Al2O3, M2O3 and M2O5 (M = As, Sb) with the respective elemental alkaline and alkaline earth elements, have been determined by single crystal X-ray diffraction. The two isotypic compounds AI 2Sb2Al2O7(K2Sb2Al2O7 structure type, AI=Rb/Cs; trigonal, space group P3̄̅m1, a = 566.04(10)/570.23(8), c = 836.8(2)/888.0(2) pm, Z = 1, R1 = 0.0511/0.0461) contain double layers consisting of vertex-sharing tetrahedra [Al2O7], which are connected to ψ- tetrahedra SbO3 via common vertices. These double layers are stacked in identical orientation (AA sequence), while in the barium compound BaSb2Al2O7 (trigonal, space group R32, a = 545.5(7), c = 2377.3(12) pm, Z = 3, R1 = 0.0427) similar layers [Sb2Al2O7] are stacked in an ABC sequence. In the arsenic(III) aluminate Cs2As2Al2O7 (orthorhombic, space group Imm2, a = 546.9(3), b = 1003.81(16), c = 888.5(3) pm, Z = 2, R1 = 0.0313) the Al2O7 moieties are similarly connected via [AsO3] units, in this case not only forming layers, but a three-dimensional network. In the three antimonates, the A cations are not coordinated by the lone electron pairs of M(III), which are oriented towards the interior of the sheets, whereas in the arsenate the lone electron pairs play a significant role in the coordination of one of the two crystallographically independent Cs sites