Single crystals of the new Zintl phases AIn 2 P 2 [A = Ca (calcium indium phosphide), Sr (strontium indium phosphide) and Ba (barium indium phosphide)] have been synthesized from a reactive indium flux. CaIn 2 P 2 and SrIn 2 P 2 are isostructural with EuIn 2 P 2 and crystallize in the space group P6 3 /mmc. The alkaline earth cations A are located at a site with 3m symmetry; In and P are located at sites with 3m symmetry. The structure type consists of layers of A 2+ cations separated by [In 2 P 2 ] 2À anions that contain [In 2 P 6 ] eclipsed ethane-like units that are further connected by shared P atoms. This yields a double layer of six-membered rings in which the In-In bonds are parallel to the c axis and to one another. BaIn 2 P 2 crystallizes in a new structure type in the space group P2 1 /m with Z = 4, with all atoms residing on sites of mirror symmetry. The structure contains layers of Ba 2+ cations separated by [In 2 P 2 ] 2À layers of staggered [In 2 P 6 ] units that form a mixture of four-, five-and six-membered rings. As a consequence of this more complicated layered structure, both the steric and electronic requirements of the large Ba 2+ cation are met. Comment Layered ternary compounds, AB 2 X 2 (A = rare earth or alkaline earth metal; B = main group, metalloid; X = main group 14-17 element) or 1-2-2 phases, favor the ThCr 2 Si 2 (I4/mmm) structure type, with the CaAl 2 Si 2 structure type (P3m1) as a distant second (Grytsiv et al., 2002; Hellmann et al., 2007). There are a few other less commonly observed structure types for layered main group metalloids, such as-BaCu 2 S 2 (Pnma; Leoni et al., 2003) observed for BaAl 2 Si 2 (Condron et al., 2007), and EuIn 2 P 2 (Jiang & Kauzlarich, 2006). In addition to inorganic compounds
, BaIn2P2. -The title compounds are prepared by reaction of the elements using an excess of indium as flux (alumina crucible in a sealed quartz tube, 1373 K, 16 h). CaIn2P2 (I) and SrIn2P2 (II) crystallize in the hexagonal space group P63 with Z = 2 and BaIn2P2 (III) in the monoclinic space group P2 1 /m with Z = 4 (single crystal XRD). The structure of (I)
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