Theoretical study of the Cu(H2O) and Cu(NH3) complexes and their photolysis products

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Abstract
Equilibrium geometries, binding energies, harmonic vibrational frequencies, infrared intensities, and isotopic shifts have been calculated for the Cu(H2O) and Cu(NH3) complexes and their photolysis products [HCuOH, CuOH, HCu(NH2), and Cu(NH2)] using Kohn–Sham theory with a gradient‐corrected nonlocal potential. Cu(H2O) and Cu(NH3) are weakly bound systems, their binding energies are estimated to be 3.7 and 12.0 kcal/mol, respectively. The HCuOH and HCu(NH2) insertion products are 2.4 and 6.3 kcal/mol less stable than Cu(H2O) and Cu(NH3), whereas H+CuOH and H+Cu(NH2) lie 49.7 and 58.0 kcal/mol above Cu(H2O) and Cu(NH3), respectively. The calculated harmonic frequencies agree remarkably well with matrix‐isolation infrared data; the agreement is always within 50 cm−1 (30 cm−1 on average) and the mean relative deviation from the experimental frequencies is 2.8%. The calculated isotopic frequency shifts are in close agreement with experiment, except for normal modes, where two or more types of vibrations are coupled. For these modes, the sum of the isotopic shifts is accurately reproduced. The sensitivity of the calculated properties to the numerical integration grid has been investigated and it is found that the grid usually used for main‐group molecules has to be extended to obtain numerically stable vibrational properties for transition metal‐ligand systems.