Abstract
The reaction of lanthanoid metal powders (Ln) with sulfur and cesium azide (CsN3) as a nitrogen source in the presence of lanthanoid tribromides (LnBr3) yields lanthanoid nitride sulfides with the composition Ln4N2S3 (Ln = Ce–Nd) when appropriate molar ratios of the starting material are used. Additional cesium bromide (CsBr) as a flux secures quantitative conversion (7 days) at 900 °C in evacuated silica tubes as well as the formation of black single crystals. All compounds crystallize isotypically with the orthorhombic crystal structure of La4N2S3 (Pnnm, Z = 2) and their structures were determined from single-crystal X-ray diffraction data (Ce4N2S3: a = 644.31(4), b = 1554.13(9), c = 404.20(3) pm; Pr4N2S3: a = 641.23(4), b = 1542.37(9), c = 400.18(3) pm; Nd4N2S3: a = 635.19(4), b = 1536.98(9), c = 397.85(3) pm). Compared to La4N2S3 the a-axes do not fulfill the expectation of the lanthanide contraction. The main feature of the crystal structure comprises N3−-centered (Ln3+)4 tetrahedra arranging as pairs [N2Ln6]12+ of edge-shared [NLn4]9+ units, which are further connected via four vertices to form double chains ∞ 1{([NLn4/2]2)6+}. Bundled along [001] like a hexagonal rod packing, they are held together by two crystallographically different S2− anions. Two compounds of a second modification (B-type La4N2S3 and Pr4N2S3) will also be presented and discussed for comparison.
Highlights
The crystal structures of all ternary lanthanide(III) nitride chalcogenides known so far (Ln3 NCh3, Ln4 N2 Ch3, Ln5 NCh6, Ln23 N5 Ch27, and Ln13 N5 Ch12 ) and their halide derivatives (Ln3 N2 ChX, Ln4 NCh3 X3, Ln5 N2 Ch4 X, Ln5 N3 Ch2 X2, and Ln6 N3 Ch4 X; lanthanoid metal powders (Ln) = La–Nd, Sm, Gd–Ho; Ch = S, Se, Te; X = Cl, Br) are dominated by N3− anions in a tetrahedral coordination of Ln3+ cations [1,2,3]
A very interesting structural behavior is exhibited by the nitride chalcogenides with the composition Ln4 N2 Ch3, which occur in seven different crystal structure types
As the main structural feature of the orthorhombic A-La4 N2 S3 -type structure [7] (Pnnm, Z = 2), N3− -centered (Ln3+ )4 tetrahedra, which first arrange as pairs [N2 Ln6 ]12+ of two edge-shared [NLn4 ]9+ units, occur
Summary
As the main structural feature of the orthorhombic A-La4 N2 S3 -type structure [7] (Pnnm, Z = 2), N3− -centered (Ln3+ ) tetrahedra, which first arrange as pairs [N2 Ln6 ]12+ of two edge-shared [NLn4 ]9+ units, occur Nd4N2Se3-type structure [8,9,10,11] (Ln = La–Nd; C2/c, Z = 4) In these compounds the [NLn4]9+ units are. Just like in A-type La4 N2 S3 but connected via two vertices to quadruples [N4Ln10]18+, which eventually build up layers and.
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