Bi2S3 Bipyramids in Layered Sulfides M2Bi2S3(AlCl4)2 (M = Ag, Cu)12. Issue 2 (18th December 2014)

• Record Type: Journal Article
• Authors: Groh, Matthias F.; Knies, Maximilian; Isaeva, Anna; Ruck, Michael
• Is Part Of: Zeitschrift für anorganische und allgemeine Chemie. Volume 641:Issue 2(2015)
• Page Start: 279
• Page End: 284
• Publication Date: 2014-12-18
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry -- Periodicals; 540
• DOI: 10.1002/zaac.201400522
• Languages: English
• ISSNs: 0044-2313

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p> Black Cu<sub>2</sub>Bi<sub>2</sub>S<sub>3</sub>(AlCl<sub>4</sub>)<sub>2</sub> and orange Ag<sub>2</sub>Bi<sub>2</sub>S<sub>3</sub>(AlCl<sub>4</sub>)<sub>2</sub> were synthesized by solvent‐free reaction (polycrystalline powders) as well as in Lewis‐acidic ionic liquids (crystals) at temperatures of 200 °C or lower. X‐ray diffraction on single‐crystals of Cu<sub>2</sub>Bi<sub>2</sub>S<sub>3</sub>(AlCl<sub>4</sub>)<sub>2</sub> revealed two centrosymmetric polytypes: a rhombohedral one, space group <italic>R</italic><inline-formula><alternatives><tex-math notation="tex"><![CDATA[$\bar{3}$]]></tex-math><inline-graphic xlink:href="ark:/27927/pgh3xswfbv0" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /></alternatives></inline-formula><italic>c</italic> [<italic>a</italic> = 658.02(3) pm, <italic>c</italic> = 6794.3(3) pm], with six formula units in the unit cell (6R polytype), and a hexagonal one, space group <italic>P</italic>6<sub>3</sub>/<italic>m</italic> [<italic>a</italic> = 658.71(6) pm, <italic>c</italic> = 2265.5(3) pm], with two formula units (2H polytype). Ag<sub>2</sub>Bi<sub>2</sub>S<sub>3</sub>(AlCl<sub>4</sub>)<sub>2</sub> is homeotypic and crystallizes in the acentric hexagonal space group <italic>P</italic><inline-formula><alternatives><tex-math notation="tex"><![CDATA[$\bar{3}$]]></tex-math><inline-graphic xlink:href="ark:/27927/pgh3xswfc3c" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /></alternatives></inline-formula>2<italic>c</italic> with <italic>a</italic> = 691.65(3) pm, <italic>c</italic> = 2207.86(9) pm, and two formula units per unit cell (2H′ polytype). All structures consist of <sup>2</sup><sub>∞</sub>[(<italic>M</italic><sup>+</sup>)<sub>2</sub>Bi<sub>2</sub>S<sub>3</sub>] layers (<italic>M</italic> = Cu, Ag) separated by double layers of AlCl<sub>4</sub><sup>–</sup> tetrahedra and differ mainly in their stacking sequences and the orientation of the AlCl<sub>4</sub><sup>–</sup> groups. The sulfidometalate layer is a honeycomb‐like network with <italic>M</italic><sup>+</sup> and S<sup>2–</sup> ions in plane, whereas pairs of Bi<sup>3+</sup> cations occupy positions above and below the plane. The analysis of chemical bonding reveals strong covalent two‐center two‐electron bonds in the five‐atomic bipyramidal Bi<sub>2</sub>S<sub>3</sub> unit (<italic>D</italic><sub>3<italic>h</italic></sub> symmetry) and covalent bonding with much higher ionic component to the coin metal cations. The DFT‐optimized shape of an isolated hypothetical Bi<sub>2</sub>S<sub>3</sub> molecule differs only marginally from that in the layer. Hence, the compounds might be interpreted as Bi<sub>2</sub>S<sub>3</sub> molecules embedded in <italic>M</italic>AlCl<sub>4</sub> salts. Optical bandgaps of 1.6 eV (<italic>M</italic> = Cu) and 2.2 eV (<italic>M</italic> = Ag) were deduced from diffuse reflectance measurements. DFT‐based quantum chemical calculations indicate direct bandgaps of the same magnitude.</p> </abstract>