Chlorodifluoroacetyl Isocyanate, ClF 2 CC(O)NCO: Preparation and Structural and Spectroscopic Studies Luis A. Ramos, † Sonia E. Ulic, † Rosana M. Romano, † Yury V. Vishnevskiy, ‡ Raphael J. F. Berger, ‡,# Norbert W. Mitzel, ‡ Helmut Beckers, § Helge Willner, § Shengrui Tong, ∥ Maofa Ge, ∥ and Carlos O. Della Ve ́ dova* ,† † CEQUINOR (UNLP-CONICET), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47 esq. 115, 1900 La Plata, Repú blica Argentina ‡ Lehrstuhl fü r Anorganische Chemie und Strukturchemie, Universitä t Bielefeld, Universitä tsstraße 25, 33615 Bielefeld, Germany § Fachbereich C - Anorganische Chemie, Bergische Universitä t Wuppertal, 42097 Wuppertal, Germany ∥ State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China * S Supporting Information ABSTRACT: Chlorodifluoroacetyl isocyanate, ClF 2 CC(O)- NCO, was prepared by the reaction of ClF 2 CC(O)Cl with excess of AgNCO. The colorless compound melts at −83 °C and the vapor pressure follows the equation ln p = −3868.3 (1/T) + 10.89 (p [Atm], T [K]) in the range −38 to +22 °C, extrapolated bp ca. 82 °C. It has been characterized by IR (gas phase, Ar matrix), liquid Raman, 19 F and 13 C NMR, gas UV− vis spectrum, photoelectron spectroscopy (PES), photo- ionization mass spectrometry (PIMS), and gas electron diffraction (GED). The matrix photochemistry has been studied and the conformational properties of ClF 2 CC(O)- NCO have been analyzed by joint application of vibrational spectroscopy, GED, and quantum chemical calculations. Two conformers were detected in gaseous and liquid phases, in which the C−Cl bond adopts a gauche orientation with respect to the CO group, whereas this group can be in syn or anti orientation with respect to the NC bond of the NCO group. An enthalpy difference ΔH exp ° = 1.3 ± 0.2 kcal mol −1 between the most stable syn−gauche and the less stable anti-gauche form was derived using the van’t Hoff equation, which is in reasonable agreement with the computed difference of ΔH° = 0.8 kcal mol −1 (B3LYP/6-311+G(3df) approximation). The most significant gas phase structural parameters for gauche−syn ClF 2 CC(O)NCO are r e (NCO) = 1.157(1) Å, r e (NCO) = 1.218(1) Å, r e (N−C) = 1.378(9) Å, r e (CO) = 1.195(1) Å, ∠ e (CNC) = 128.6(19)°. Photolysis of ClF 2 CC(O)NCO using an ArF excimer laser (193 nm) mainly yield ClF 2 CNCO along with some ClF 2 CC(O)N nitrene. The valence electronic properties of the title compound were studied using the PES and PIMS. The experimental first vertical ionization energy of 11.54 eV corresponds to the ejection of a carbonylic oxygen lone pair electron. ■ INTRODUCTION Isocyanates, i.e., derivatives of the isocyanic acid, have a wide range of applications, but also present very basic challenges. They are precursors in the formation of polyurethane polymers and thus have a variety of important technological applica- tions 1,2 including adhesives, sealants and paints, and flexible and rigid foams. However, fundamental aspects of the isocyanates are also of interest. Off-axis substitution on a pseudohalogen of the type azide, isothiocyanate, or isocyanate leads to interesting spectroscopic consequences caused by splitting of the π degeneration. 3 Our fundamental studies on the bonding and properties of isocyanates containing molecules has included a large series of molecules: S(NCO) 2 , FC(O)NCO, ClC(O)NCO, BrC(O)- NCO, CH 3 C(O)NCO, FSO 2 NCO, ClSO 2 NCO, CF 3 SO 2 NCO, F 2 NC(O)NCO, ClCH 2 CH 2 NCO, FC(O)- SNCO, CH 3 OC(O)SNCO, OV(NCO) 3 , ONNCO, N 3 NCO, FNCO, and CClF 2 NCO (see refs 4−6 and references cited therein). These contributions include preparation, chemical, physical, and spectroscopic studies of the compounds. The molecule ClC(O)NCO challenges the reliability of ab initio calculations. 7 The conformational properties of the molecules XC(O)NCO (X = F, Cl, Br, and CH 3 ) are of interest: the syn conformation in equilibrium with a lower concentration of the anti form seems to be preferred for Cl, Br, and CH 3 compounds, whereas for FC(O)NCO the anti rotamer (65%) is the most stable form. Very few molecules provide vibrational spectra so rich in information as FC(O)NCO. 8 Received: September 27, 2012 Revised: November 1, 2012 Published: November 1, 2012 Article pubs.acs.org/JPCA © 2012 American Chemical Society 11586 dx.doi.org/10.1021/jp3096055 | J. Phys. Chem. A 2012, 116, 11586−11595