Three Unique Barium Manganese Vanadates from High-Temperature Hydrothermal Brines.

Three new barium manganese vanadates, all containing hexagonal barium chloride layers interpenetrated by [V2 O7 ]4- groups, were synthesized using a high-temperature (580 °C) hydrothermal method. Two of the compounds were prepared from a mixed BaCl2 /Ba(OH)2 mineralizer, and the third compound was prepared from BaCl2 mineralizer. An interesting structural similarity exists between two of the compounds, Ba2 Mn(V2 O7 )(OH)Cl and Ba4 Mn2 (V2 O7 )(VO4 )2 O(OH)Cl. These two compounds crystallize in the orthorhombic space group Pnma, Z = 4, and are structurally related by a nearly doubled a axis. The first structure, Ba2 Mn(V2 O7 )(OH)Cl (I) (a = 15.097(3) Å, b = 6.1087(12) Å, c = 9.5599(19) Å), consists of octahedral manganese(II) edge-sharing chains linked by pyrovanadate [V2 O7 ] groups, generating a three-dimensional structure. Compound II, Ba4 Mn2 (V2 O7 )(VO4 )2 O(OH)Cl (a = 29.0814(11) Å, b = 6.2089(2) Å, c = 9.5219(4) Å), is composed of manganese(III) edge-sharing chains that are coordinated to one another through pyrovanadate groups in a nearly identical way as in I, forming a zigzag layer. A key difference in II is that these layers are capped on either end by two monomeric [VO4 ] groups that directly replace one [V2 O7 ] group in I. The third compound, Ba5 Mn3 (V2 O7 )3 (OH,Cl)Cl3 (III), crystallizes in the trigonal space group R32 (a = 9.7757(4) Å, c = 22.4987(10) Å) and is composed of manganese(II) trimeric units, [Mn3 O12 (OH,Cl)], coordinated to one another through pyrovanadate [V2 O7 ] groups to form a three-dimensional structure. The unusual manganese trimers are built of three square pyramids all linked by a central (OH/Cl) atom. The key factor directing the formation of the different structures appears to be the identity and concentration of the halide brine mineralizer fluid. The ability of such brines to induce the formation of interpenetrated salt lattices in the present study is suggestive of a versatile realm of descriptive synthetic inorganic chemistry.