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Ytterbium(III) Tricyanomethanides with Sodium and Potassium: Similarities and Differences Between NaYb[C(CN)3]4 and
Ralf J C Locke1, Giuseppe Montana2, Robert U Stelzer1
1Institute for Inorganic Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
Abstract:
Metathesis reactions of Ag[C(CN)3] with anhydrous YbCl3 dissolved in water combined with stoichiometric amounts of the alkali-metal salts A[C(CN)3] (A = Na or K) yield the non-isotypic tetragonal compounds NaYb[C(CN)3]4 (P4/nnc with a = 1188.37(9) pm, c = 1232.41(9) pm) and KYb[C(CN)3]4 (P4/nbm with a = 1179.26(9) pm, c = 668.73(5) pm). Both crystal structures contain a three-dimensional framework (Niggli formula: 3∞{(Yb[C(CN)3]8/2)-}) with Yb3+ in square antiprismatic coordination of terminal nitrogen atoms (d(Yb-N) = 241-242 pm) from eight planar star-shaped tricyanomethanide anions [C(CN)3]-. The Na+ or K+ cations occupy vacancies, which provide them with a tetrahedral coordination sphere of nitrogen (d(Na-N) = 239 pm vs. d(K-N) = 276 pm) from four [C(CN)3]- anions. This difference results from secondary contacts with the central carbon atoms (d(Na-C) = 361 pm vs. d(K-C) = 367 pm) of four different [C(CN)3]- units, which do not contribute to NaYb[C(CN)3]4, but effectuate a lot in the case of KYb[C(CN)3]4. The Raman spectrum recorded for NaYb[C(CN)3]4 corroborates the presence of a pseudo-D3h-symmetric tricyanomethanide anion [C(CN)3]- and the absence of water.
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