Extended frameworks encapsulating facial {MoO3} units: Syntheses and structural characterizations of Ba-3(MoO3)(3)(H2O)(3)(H2O)(AsO4)(2), SrMoO3HAsO4center dot H2O, and Sr(MoO2AsO4)(2)

Three new alkaline earth metal molybdenum(VI) arsenates, Ba-3(MoO3)(3)(H2O) (AsO4)(2) (1), SrMoO3HAsO4. H2O (2), and Sr(MoO2AsO4)(2) (3), have been pre pared and structurally characterized by single-crystal X-ray diffract;ion a nd thermogravimetric analysis. Crystal data: 1, monoclinic, P2(1)/c, a = 10 .1814(2) Angstrom, b = 17.5553(1) Angstrom, 17.0799(1) Angstrom, beta = 90. 349(1)degrees, V = 3052.75(7) Angstrom(3), and Z = 8; 2, monoclinic, C2/c, a = 15.1927(11) Angstrom, b = 10.2590(8) Angstrom, c = 9.6550(7) Angstrom, beta = 121.877(1)degrees, V = 1277.9(3) Angstrom(3), and Z = 8; 3, monoclin ic, P2(1)/c, a = 6.5904(3) Angstrom, b = 6.8592(3) Angstrom, c = 10.4472(5) Angstrom, beta = 92.106(2)degrees, V = 471.94(6) Angstrom(3), and Z = 2. C rystal 1 adopts a novel open-framework structure which is composed of isola ted MoO6 and Mo(H2O)O-5 octahedra linked by AsO4 tetrahedra, resulting in i ntersecting tunnels where Ba2+ cations reside. Crystal 2 has a layer struct ure in which MoO6 octahedra are corner-shared with HAsO4 tetrahedra forming infinite sheets parallel to the (100) planes. The Sr2+ cations and water m olecules are between the layers. Crystal 3 adopts a tunnel structure which is isotypic with the phosphates A(MoO2PO4)2 (A = Ba, Pb). As a common featu re, all of the MoO6 octahedra possess three terminal O2- ions in 1 and 2. T hey are the first extended structures encapsulating facial {MoO3} units. Th ermal analysis and powder X-ray diffraction studies revealed that these uni ts in 2 would progressively dissociate into cis {MoO2} cores under heating, resulting in the structural transformation into 8. In this paper, the synt heses, crystal structures, thermogravimetric studies, and structural relati onship are presented.