In2.24(NCN)3 and NaIn(NCN)2: Synthesis and Crystal Structures of New Main Group Metal Cyanamides
نویسنده
چکیده
Single crystals of In2.24(N CN )3 and N aIn(NCN)2 can be synthesized from a reaction be tween InBr and NaCN at 400 °C, followed by chemical transport at 400-500 °C. The X-ray crystal structure determinations of In2.24(NCN)3 (rhombohedral R 3c, a = 606.09(4), c 2884.4(2) pm, Z = 6) and NaIn(NCN)2 (orthorhombic Cmcm, a = 961.30(6), b = 716.84(5), c = 603.65(4) pm, Z = 4) reveal ionic layer structures built from sheets of cationic and anionic (cyanamide) motifs. While NaIn(NCN)2 contains In3+ and Na+ ions, In2 24(NCN)3 is a mixedvalence compound, incorporating a monovalent In+ ion besides trivalent indium. The NCN2~ units of both In2,24(NCN)3 and NaIn(NCN)2 reflect perfect D xll point group symmetry within the limits of experimental accuracy. Furthermore, an evaluation of all presently available crystallographic data on metal cyanamide crystal structures manifests that there is no evi dence for a non-centrosymmetric description of any of these. Likewise, we propose an alter native centrosymmetric structural model for lead cyanamide, PbNCN, and question the evi dence of the unsymmetrical, non-Dxh shaped cyanamide anion in the latter structure.
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تاریخ انتشار 2013