[Cu(NH3)(5)](2+) in the crystal lattice of [Cu(NH3)(5)](ClO4)(2) form a trigonal bi-pyramid (D-3h) and/or a square-based pyramid (C-4v), both with the rotating NH3. Both structures were adopted for the quantum chemical calculations for isolated [Cu(NH3)(5)](2+) vibrations, but because the rotation of NH3 was not possible to simulate the point symmetry was lowered to C-3h and C-1. The calculated energy of equilibrium geometry and vibrational infrared and Raman spectra for both models are practically identical. A dynamic transition is possible between both types of the cation structure. An agreement between the experimental and calculated spectra confirmed the appropriateness of the used models. (C) 2003 Elsevier B.V. All rights reserved.