MnPO4

MnPO4 is a chemical designation used in discussions of manganese phosphates. In standard inorganic chemistry there is no stable, simple binary salt with formula MnPO4: combining Mn2+ with PO4^3- would yield a charged species. Instead, manganese forms polyphosphates such as Mn3(PO4)2 (manganese(II) phosphate) and protonated solids such as MnHPO4 (manganese(II) hydrogen phosphate), along with various hydrated forms. The term MnPO4 is sometimes used in materials science to refer to the anhydrous MnPO4 framework that appears as the end member of the lithium manganese phosphate family, LiMnPO4, which is studied as a cathode material in lithium-ion batteries.

Various crystal structures exist depending on the phase. Mn3(PO4)2 can crystallize in several polymorphs and is generally insoluble in water. MnHPO4 forms a separate phase, often with water coordinated in hydrates. The LiMnPO4 end member adopts an olivine-type framework in which Mn resides in octahedral sites linked by PO4 tetrahedra.

Synthesis approaches include precipitation of Mn3(PO4)2 from manganese salts with phosphate under controlled pH, hydrothermal methods, and solid-state reactions. MnHPO4 and hydrated derivatives can be prepared by adjusting the stoichiometry and pH of Mn2+-containing phosphate solutions.

Applications of manganese phosphates span ceramics, pigments, and precursors to manganese-containing materials. In electrochemistry, LiMnPO4-based compounds have drawn attention as potential cathodes for lithium-ion batteries due to their stability and redox behavior.

See also: manganese phosphate, LiMnPO4, olivine phosphate, manganese minerals.