Tricyanidoferrates(-IV) and Ruthenates(-IV) with Non-Innocent Cyanido Ligands.

Exceptionally electron-rich, nearly trigonal-planar tricyanidometalate anions [Fe(CN)3]7- and [Ru(CN)3]7- were stabilized in LiSr3[Fe(CN)3] and Ae3.5M(CN)3] (Ae = Sr, Ba; M = Fe, Ru). They are the first examples of group 8 elements with the oxidation state of -IV. Microcrystalline powders were obtained by a solid-state route, single-crystals from alkali metal flux. While LiSr3[Fe(CN)3] crystallizes in P 63/m , the polar space group P 63 with three-fold cell volume for Ae3.5[M(CN)3] is confirmed by second harmonic generation. X-ray diffraction, IR and Raman spectroscopy reveal longer C-N distances (124-128 pm) and much lower stretching frequencies (1484-1634 cm-1 ) than in classical cyanidometalates. Weak C-N bonds in combination with strong M -C π-bonding is a scheme also known for carbonylmetalates. Instead of the formal notation [Fe-IV(CN-)3]7-, quantum chemical calculations revealed non-innocent intermediate-valent CN1.67- ligands and a closed-shell d10 configuration for Fe, i.e. Fe2- .