In_2.24(NCN)₃ and NaIn(NCN)₂: Synthesis and Crystal Structures of New Main Group Metal Cyanamides

Abstract

In an attem p t to synthesize indium cyanides containing m onovalent indium from th e p re c u r sors indium m onobrom ide InB r and sodium cya nide NaCN, we accidentally found tw o new and unexpected indium cyanam ides in crystalline form , nam ely In224(N C N )3 and N aIn (N C N )2. In the following, we report on their synthesis and crys tal structures. Experimental Details SynthesisA 1:1 m ixture of freshly prep ared [6], powderous InB r and dry pow dery N aC N (M erck, reinst) was filled into an evacuated glass tube and heated at 400 °C for 1 week. The product, a black pow dery m aterial covered with tiny solidified drops of m etallic indium , was then filled into an o th e r evacuated glass am poule and subjected to a tem p eratu re gradient of 4 0 0 -5 0 0 °C for one m onth.In the h o tter part of the am poule, colorless, tra n sp a re n t crystals of needle-like shape are form ed, later identified as N aIn (N C N )2. The colder p a rt of the am poule contains tran sp aren t, com pact am ber-like crystals, later designated as In2 24(N C N )3. Besides these two com pounds, the rem aining brow n pow der shows the characteristic reflections of sodium brom ide, NaBr.Crystals of In2 24(N C N )3 and N aIn (N C N )2 seem to exhibit a m oderate sensitivity with respect to air 0932-0776/95/0800-1245 $06.00 © 1995 Verlag der Zeitschrift für Naturforschung. All rights reserved. Unauthenticated Download Date | 5/11/18 2:36 AM

A Ferromagnetic Carbodiimide: Cr2(NCN)3

“…In addition, there is related information with respect to existing rare-earth metal(III) carbodiimides. Recent research on such Ln 2 (NCN) 3 phases by others [5d,e] provided similar layer structures to those of the MNCN phases but with different coordination modes. The changes in coordination mode must result in different magnetic exchange couplings, and that is what we were looking for.…”

“…The compound appears to be highly inert. Not too surprisingly, the structural determination yields that Cr 2 (NCN) 3 is isostructural with Yb 2 (NCN) 3 .…”

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Extended pseudochalcogenides such as the solid-state carbodiimides (incorporating complex À N = C = N À units with D 1h symmetry) or cyanamides (with a less symmetrical N C À N 2À unit) have been extensively investigated, and a large number including alkali [1] and alkaline-earth metals, [2] main-group elements, [3] d 10 transition metals, [4] and also rare-earth metals [5] have been reported. The synthesis of the complete set of MNCN (M = Mn-Cu) phases with only partially filled 3d orbitals, however, looked far more difficult, because firstprinciples calculations [6] had predicted them to be unstable in terms of formation enthalpy DH f and Gibbs formation energy DG f , with the instability continuously rising from MnNCN to CuNCN, thereby mirroring the gradual filling of antibonding levels from 3d 5 to 3d 9 .

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“…The hypothetical chromium(III) carbodiimide, Cr 2 -(NCN) 3 , is such a synthetic target although its isolobal oxide Cr 2 O 3 is, in fact, antiferromagnetic. Because the electron configuration (3d 3 ) is even lower than in the MnNCN case, theory [6] implies that the synthetic route for MnNCN should also be applicable for Cr 2 (NCN) 3 . In addition, there is related information with respect to existing rare-earth metal(III) carbodiimides.…”

“…We have now synthesized green Cr 2 (NCN) 3 , the first transition-metal(III) carbodiimide with a 3d 3 configuration, by a metathesis between CrCl 3 and freshly made ZnNCN. The compound appears to be highly inert.…”