Extended Frameworks Encapsulating Facial {MoO3} Units:  Syntheses and Structural Characterizations of Ba3(MoO3)3(H2O)(AsO4)2, SrMoO3HAsO4·H2O, and Sr(MoO2AsO4)2

• Published in: Chemistry of materials 1999-07, Vol.11 (7), p.1876-1882
• Main Authors: Hsu, Kuei-Fang, Wang, Sue-Lein
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm990072t

Three new alkaline earth metal molybdenum(VI) arsenates, Ba3(MoO3)3(H2O)(AsO4)2 (1), SrMoO3HAsO4·H2O (2), and Sr(MoO2AsO4)2 (3), have been prepared and structurally characterized by single-crystal X-ray diffraction and thermogravimetric analysis. Crystal data:  1, monoclinic, P21/c, a = 10.1814(2) Å, b = 17.5553(1) Å, c = 17.0799(1) Å, β = 90.349(1)°, V = 3052.75(7) Å3, and Z = 8; 2, monoclinic, C2/c, a = 15.1927(11) Å, b = 10.2590(8) Å, c = 9.6550(7) Å, β = 121.877(1)°, V = 1277.9(3) Å3, and Z = 8; 3, monoclinic, P21/c, a = 6.5904(3) Å, b = 6.8592(3) Å, c = 10.4472(5) Å, β = 92.106(2)°, V = 471.94(6) Å3, and Z = 2. Crystal 1 adopts a novel open-framework structure which is composed of isolated MoO6 and Mo(H2O)O5 octahedra linked by AsO4 tetrahedra, resulting in intersecting tunnels where Ba2+ cations reside. Crystal 2 has a layer structure in which MoO6 octahedra are corner-shared with HAsO4 tetrahedra forming infinite sheets parallel to the (100) planes. The Sr2+ cations and water molecules 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 feature, all of the MoO6 octahedra possess three terminal O2- ions in 1 and 2. They are the first extended structures encapsulating facial {MoO3} units. Thermal analysis and powder X-ray diffraction studies revealed that these units in 2 would progressively dissociate into cis {MoO2} cores under heating, resulting in the structural transformation into 3. In this paper, the syntheses, crystal structures, thermogravimetric studies, and structural relationship are presented.