Gas phase complexes of H3N•••CuF and H3N•••CuI studied by rotational spectroscopy and ab initio calculations: the effect of X (X = F, Cl, Br, I) in OC•••CuX and H3N•••CuX

Complexes of H3N center dot center dot center dot CuF and H3N center dot center dot center dot CuI have been synthesised in the gas phase and characterized by microwave spectroscopy. The rotational spectra of 4 isotopologues of H3N center dot center dot center dot CuF and 5 isotopologues of H3N center dot center dot center dot CuI have been measured in the 6.5-18.5 GHz frequency range using a chirped-pulse Fourier transform microwave spectrometer. Each complex is generated from a gas sample containing NH3 and a halogen-containing precursor diluted in Ar. Copper is introduced by laser ablation of a solid target prior to supersonic expansion of the sample into the vacuum chamber of the microwave spectrometer. The spectrum of each complex is characteristic of a symmetric rotor and a C-3v geometry in which the N, Cu and X atoms (where X is F or I) lie on the C-3(a) axis. The rotational constant (B-0), centrifugal distortion constants (D-J and D-JK), nuclear spin-rotation (C-bb(Cu) = C-cc(Cu)) constant (for H3N center dot center dot center dot CuF only) and nuclear quadrupole coupling constants (chi(aa)(X) where (X = N, Cu, I)) are fitted to the observed transition frequencies. Structural parameters are determined from the measured rotational constants and also calculated ab initio at the CCSD(T)(F12*)/AVQZ level of theory. Force constants describing the interaction between ammonia and each metal halide are determined from D-J for each complex. Trends in the interaction strengths and geometries of B center dot center dot center dot CuX (B = NH3, CO) (X = F, Cl, Br, I) are discussed.