Cu~(II) in Liquid Ammonia: An Approach by Hybrid Quantum-Mechanical/MoIecuIar-IVIechanical Molecular Dynamics Simulation

摘要

To investigate the solvation structure of the Cu~(II) ion in liquid ammonia, ab initio quantum-mechanical/molecular-mechanical (QM/MM) molecular dynamics (MD) simulations were carried out at Hartree Fock (HF) and hybrid density functional theory (B3LYP) levels. A sixfold-coordinated species was found to be predominant in the HF case whereas five- and sixfold-coordinated complexes were obtained in a ratio 2:1 from the B3 LYP simulation. In contrast to hydrated Cu; which exhibits a typical Jahn - Teller distortion, the geometrical arrangement of ligand molecules, in the case of ammonia can be described as a [2+4] ([2+3]) configuration with 4 (3) elongated copper-nitrogen bonds. First shell solvent exchange reactions at picosecond rate took place in both HF and B3 LYP simulations, again in contrast to the more stable sixfold-coordinated hydrate. NH_3 ligands apparently lead to strongly accelerated dynamics of the Cwsolvate due to the "inverse" [2+4] structure with its larger number of elongated copper-ligand bonds. Several dynamical properties, such as mean ligand residence times or ion-ligand stretching frequencies, prove the high lability of the solvated complex.