Electronic and molecular structure of [Cr(N)(NCO)4]2−, the first example of a mixed nitride–cyanate complex

Metathesis of [Cr(N)Cl4]2− with excess cyanate affords the title complex which is the first example of a nitride complex with only cyanate auxiliary ligands. The electronic spectrum allows assignment of the ligand field transitions: B1(C4v) ← B2(C4v) and E(C4v) ← B2(C4v). From these data, cyanate can be deduced to be intermediate between azide and thiocyanate with respect to σ-donation and comparable to thiocyanate, but weaker than azide with respect to π-donation. Solution EPR demonstrates the cyanate ligands to be N-bonded with similar super-hyperfine couplings to all nitrogen ligators, and the X-ray crystal structure of (Ph3PNPPh3)2[Cr(N)(NCO)4] (1) establishes the expected 5-coordinate square pyramidal structure with a short Cr–N(nitride) bond, 1.520(5) Å and chromium–cyanate bond lengths in the range 1.948(12)–2.05(2) Å.