(Sr6N)[CoN2][CN2]2: The first low-valency nitridometalate carbodiimide

The first nitridocobaltate carbodiimide (Sr6N)[CoN2][CN2]2 has been synthesized from the elements Sr, Co, and graphite powder and NaN3 (as a nitrogen source). The crystal structure was determined from X-ray single-crystal diffraction data as orthorhombic (space group P21212, No. 18, a=9.8807(6) Å, b=14.6474(9) Å, c=3.8569(3) Å, V=558.2 Å3, Z=2, R1=0.0265, wR2=0.0383). (Sr6N)[CoN2][CN2]2 is the first low-valency 3d-transition nitridometalate containing additional [CN2]2− groups. The crystal structure can be described as an array of rocksalt-like columns of Sr and N linked via common corners and connected by [NCN]2− and [CoIN2]5− units located within structural channels running along [0 0 1]. The magnetic susceptibility follows the Curie-Weiss law with an effective moment of 3.26 μB consistent with two unpaired spins (d8, CoI). The compound is a bad metallic conductor with a resistivity of order 1 mΩ cm at 300 K. Vibrational spectroscopic data support the existence of carbodiimide [NCN]2− species. The Co K-edge X-ray absorption spectra (XAS) of Ca5[CoN2]2 and (Sr6N)[CoN2][CN2]2 confirm the presence of CoI within the complex anions.