A Remarkable Change in Framework Cation Positions upon Lithium Exchange: the Crystal Structure of LiMnPO4(OH)

A migration of Mn3+ ions into previously unoccupied octahedral holes, while the oxygen and the phosphorus sites remain virtually unchanged, takes place in the course of the reaction of MnPO4. H2O with LiNO3 to give the title compound (see polyhedral representation right; Li atoms as open circles, MnO6 octahedra and PO4 tetrahedra, H atoms omitted). These crystal-chemical effects are surprising, but such topotactic reactions are also of interest for the preparation of novel materials, for example for batteries and ionic conductors.