Flux growth and structure of two compounds with the EuIn₂P₂structure type,AIn₂P₂(A= Ca and Sr), and a new structure type, BaIn₂P₂

Abstract

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

Low-Dimensional Nitridosilicates Grown from Ca/Li Flux: Void Metal Ca8In2SiN4 and Semiconductor Ca3SiN3H

“…The indium–indium bond length is 3.0654(7) Å. This is contrary to shorter bond lengths found in compounds such as Ba 2 In 5 Pn 5 (Pn = P, As; In–In = 2.750(1)–2.776(1) Å and 2.757(1)–2.777(1) Å respectively) and AIn 2 Pn 2 (A = Eu, Ca, Sr, or Ba); In–In = 2.7608(10), 2.7625(19) Å, 2.7620(13) Å, and 2.7460(10)–2.8161(10) Å respectively), where indium atoms are in a more covalent environment bonded to pnictides. − Zintl phases such as NaIn, CaIn 2 , and BaIn 2 where indium forms 3-D nets have comparatively longer In–In bond lengths (3.175 Å, 2.92–3.13 Å, and 2.97–3.12 Å respectively) . These bond lengths are comparable to the indium dimers within Ca 8 In 2 SiN 4 .…”

“…These dimers are slanted at a 29° angle to the ac -plane and alternate down the c -axis along a 2 1 screw-axis. In–In bonding is not uncommon in intermetallics and occurs as 1-D zigzag chains (Ca 4 In 2 N and Ca 2 InN), 3D nets (NaIn, CaIn 2 , SrIn 2 , and BaIn 2 ), and ethane-like units Pn 3 In-InPn 3 , where Pn = pnictide, which may be eclipsed or anti conformation (CaIn 2 P 2 , SrIn 2 P 2 , EuIn 2 P 2 , Ba 2 In 5 P 5 , and Ba 2 In 5 As 5 ). − While indium does form In–In dimers within ethane-like units, or in Ge–In–In-Ge- zigzag chains within SrCa 2 In 2 Ge, isolated indium dimers surrounded by electropositive cations are unknown . Structures of binary intermetallics of indium and electropositive metals (such as CaIn 2 and SrIn 2 ) usually contain a 3-D network of In–In bonding .…”

New insights into the application of the valence rules in Zintl phases—Crystal and electronic structures of Ba7Ga4P9, Ba7Ga4As9, Ba7Al4Sb9, Ba6CaAl4Sb9, and Ba6CaGa4Sb9

“…A variety of new ternary AE-Tr-Pn pnictides (AE¼Ca, Sr, Ba; Tr ¼Al, Ga, In; and Pn ¼P, As, Sb) have been reported in recent years, including BaGa 2 Pn 2 [1], Ba 2 Ga 5 As 5 , CaGa 2 Pn 2 , and SrGa 2 As 2 [2], AE 3 Al 2 Pn 4 and AE 3 Ga 2 Pn 4 [3], Ba 3 Al 3 Pn 5 and Ba 3 Ga 3 P 5 [4], discovered by our group, and BaGa 2 Sb 2 [5], Ba 3 Ga 4 Sb 5 [6], BaIn 2 P 2 [7], Ba 2 In 5 As 5 [8], among others, reported by teams from all over the world. In these compounds, significant differences in the electronegativities of the constituent elements imply complete electron transfer from electropositive alkaline-earth metals to (poly)anionic networks made up of electronegative metalloid elements, which form covalent bonds to attain closed-shell configuration.…”

Gallium Pnictides of the Alkaline Earth Metals, Synthesized by Means of the Flux Method: Crystal Structures and Properties of CaGa2Pn2, SrGa2As2, Ba2Ga5As5, and Ba4Ga5Pn8 (Pn = P or As)

“…cussed, [29][30][31] we will only point out several important features, mainly in comparison with the structure of CaGa 2 As 2 , which is similar but not identical.…”

“…Other known compounds that crystallize with the same structure type include EuIn 2 As 2 , [30] CaIn 2 P 2 , and SrIn 2 P 2 . [31] 2-double layers, which are stacked along the direction of the c axis ( Figure 1). The divalent Ca 2+ and Sr…”