Four‐Coordinate Copper Halonitrosyl {CuNO}10 Complexes

While copper nitrosyl complexes are implicated in numerous biological systems, isolable examples remain limited. In this report, we show that [Cl3CuNO]−, with a {CuNO}10 electron configuration, can be generated by nitrite reduction at a copper(I) dichloride anion or by nitric oxide addition to a copper(II) trichloride precursor. The bromide analogue, [Br3CuNO]− was synthesized analogously, and both copper halonitrosyl complexes were characterized by X‐ray diffraction and a variety of spectroscopic methods. Experimental data and multireference (CASSCF/NEVPT2) calculations provide strong evidence for a CuII–NO. ground state. Both [Cl3CuNO]− and [Br3CuNO]− release and recapture NO. reversibly, and exhibit nitrosative reactivities toward a wide range of biological nucleophiles, such as amines, alcohols, and thiols.