Gas phase structure of O-nitrobis(trifluoromethyl)hydroxylamine, (CF3)2NONO2: an extremely long O-N bond.

The gas phase structure of O-nitrobis(trifluoromethyl)hydroxylamine, (CF(3))(2)NONO(2), has been determined with gas electron diffraction and quantum chemical calculations (HF, MP2, and B3LYP with 6-31G basis sets). The calculations predict a structure with C(s) overall symmetry, a planar NONO(2) skeleton, and the NO(2) group oriented anti with respect to the CNC plane. The electron diffraction intensities are reproduced very well with such a model. The molecule possesses pyramidal configuration at the amino nitrogen atom, and the following geometric parameters (r(a) values with 3sigma uncertainties) were obtained for the NONO(2) skeleton: N-O = 1.392(18) A, O-N = 1.597(16) A, N=O(mean) = 1.192(4) A, N-O-N = 106.9(25) degrees, O=N=O = 138.4(24) degrees. The extremely long O-N distance is rationalized by very weak bonding between the two stable radicals (CF(3))(2)NO and NO(2). Whereas the ab initio methods HF O-N = 1.395 A and MP2 O-N = 1.664 A fail to reproduce this bond length correctly, the hybrid method B3LYP O-N = 1.584 A results in good agreement.