Structure of Na2AlBAs4O14, a condensed aluminoboroarsenate

Mr=607.45, monoclinic, P21/c, a=4.5916(5), b=20.706(3), c=10.933(1) A, β=90.39(1)0, V=1039.4 A3, Z=4, Dx=3.88, Dm (in bromobenzene)=3.93 Mg m-3, MoK anti α, λ=0.7107 A, μ=13.7 mm-1, F(000)=1136, T=293 K, R=0.035, ωR=0.047 for 1029 independent reflections. The main feature of this structure is the existence of a novel aluminoboroarsenate anion (Al2B2As8O28)4n-n built up from centrosymmetrical B2As4O18 rings formed by corner-sharing of AsO4 and BO4 tetrahedra and having two As2O7 pyroarsenate branches. The rings form infinite chains parallel to the a direction by As-O-B linkages. The chains are linked by sharing edges of AsO4 tetrahedra and AlO6 octahedra to form an infinite three-dimensional framework containing tunnels parallel to the chains where the Na+ cations are located. This structure is the first ternary heteropolyanion including B, Al and As atoms. (orig.)