Novel phosphate halides BaMn^III[PO₄]FCl and BaMn^III[PO₄]F₂: Effects of mixed halides on crystal structures and magnetic properties

Two new phosphate halides BaMn^III[PO₄]FCl (1) and BaMn^III[PO₄]F₂ (2), have been synthesized under hydrothermal conditions. Structural characterizations show that both new compounds adopt layered structures but with different polyhedral linkages. Introduction of Cl into Compound (1) results in isolated hemimorphic [MnO₄FCl] octahedra, different from the chain of [MnO₄F₂]/[MnO₂F₄] octahedra in Compound (2). These compounds have significantly different molecular vibration modes and thermal stabilities. Magnetic measurements reveal that Compound (2) has larger antiferromagnetic interactions than Compound (1), because the former has strong interactions between Mn³⁺-Mn³⁺ ions within corner-shared Mn³⁺-octahedral chains whereas the latter only possesses isolated Mn³⁺-octahedra. Both compounds transform to a new orthorhombic compound BaMn^II(PO₄)F (3) after thermal decomposition.