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

Abstract

Metathesis of [Cr(N)Cl 4 ] 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: B 1 (C 4v ) ← B 2 (C 4v ) and E(C 4v ) ← B 2 (C 4v ). 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 (Ph 3 PNPPh 3 ) 2 [Cr(N)( N CO) 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. As the first example of a complex with only nitride and cyanate ligands, [Cr(N)(NCO) 4 ] 2− was prepared by metathesis from the chloro complex. The cyanate ligands are N-bonded and intermediate between azide and thiocyanate in ligand field strength. ► Metathesis reactions of Cr(V) nitride complexes. ► Structural comparison of pseudo halide complexes. ► d–d transitions in UV–vis spectroscopy. ► Cyanate ligand-field strength. ► Fitting of EPR spectral traces.