Hydrothermal Synthesis and Structures of Two Tetramethylammonium Iron Molybdates (TMA)2FeMo6O20and [TMA]2[Fe(H2O)6]Mo8O26

Two new compounds (TMA)2FeMo6O20and [TMA]2[Fe(H2O)6]Mo8O26have been synthesized by hydrothermal reactions. (TMA)2FeMo6O20crystallizes in the monoclinic space groupC2/m;a=21.204(1) ?b=7.6393(5) ?,c=8.4191(6) ?,=104.602 (1)°,V=1319.7(2) ?3,Z=2, (R=2.23%,I>2(I)) [TMA]2[Fe(H2O)6]Mo8O26crystallizes in the space groupP21/n;a=10.3945 (5) ?,b=16.4103(8) ?,c=10.8935(5) ?,=98.842(1)°,V=1836.1(2) ?3,Z=2 (R=2.07%I>2(I)). The structures of both compounds were determined by single crystal X-ray methods. The crystal structure of (TMA)2FeMo6O20consists of2 [FeMo6O20]2-layers separated by layers of tetramethylammonium cations. The [FeMo6O20]2-layers are built up by the interconnection of corner- and edge-sharing MoO6octahedral chains through FeO6octahedra. The arrangement of MoO6octahedra in the chains is identical to that found in the red potassium molybdenum bronze structure. In the (TMA) 2FeMo6O20structure, the chains are connected into layers by bridging FeO6octahedra, in contrast to the bronze structure, where the chains are directly connected by sharing oxygen atoms. The structure of [TMA]2[Fe(H2O)6]Mo8O26is made up by packing of octahedral [Fe(H2O)2+6] cations and-[Mo8O4-26] cluster anions. These building units are interconnected through hydrogen bonds. Tetramethylammonium cations provide charge balance.