Three Unique Barium Manganese Vanadates from High-Temperature Hydrothermal Brines

Three new barium manganese vanadates, all containing hexagonal barium chloride layers interpenetrated by [V₂O₇]^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, Ba₂Mn­(V₂O₇)­(OH)Cl and Ba₄Mn₂(V₂O₇)­(VO₄)₂O­(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, Ba₂Mn­(V₂O₇)­(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 [V₂O₇] groups, generating a three-dimensional structure. Compound II, Ba₄Mn₂(V₂O₇)­(VO₄)₂O­(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 [V₂O₇] group in I. The third compound, Ba₅Mn₃(V₂O₇)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, [Mn₃O₁₂(OH,Cl)], coordinated to one another through pyrovanadate [V₂O₇] 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.