Synthesis, Crystal Structure and Charge-distribution Validation of a New Alluaudite-type Phosphate, NaMnIn(PO)

NaMnIn(PO, sodium manganese indium tris-(phosphate) (2.22/0.87/1.68), was obtained in the form of single crystals by a flux method and was structurally characterized by single-crystal X-ray diffraction. The compound belongs to the alluaudite structure type (space group 2/) with general formula (2)(1)(1)(2)(PO). The (2) and (1) sites are partially occupied by sodium [occupancy 0.7676 (17) and 1/2] while the (1) and (2) sites are fully occupied within a mixed distribution of sodium/manganese(II) and manganese(II)/indium, respectively. The three-dimensional anionic framework is built up on the basis of (2)O dimers that share opposite edges with (1)O octa-hedra, thus forming infinite chains extending parallel to [10]. The linkage between these chains is ensured by PO tetra-hedra through common vertices. The three-dimensional network thus constructed delimits two types of hexa-gonal channels, resulting from the catenation of (2)O dimers, (1)O octa-hedra and PO tetra-hedra through edge- and corner-sharing. The channels are occupied by Na cations with coordination numbers of seven and eight.