The A-Type Ln4N2S3 Series: New Nitride Sulfides of the Light Lanthanoids (Ln = Ce–Nd)

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 (Ln)4 tetrahedra arranging as pairs [N2Ln6] of edge-shared [NLn4] units, which are further connected via four vertices to form double chains 1 ∞{([NLn4/2]2)}. 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.