We present the results of calculations of the {[FeCl_6-n(CN)_n]^m-×(V_Na)_5-m}^5- impurity complex incorporated in the NaCl crystal lattice. A number of characteristic defect configurations are calculated quantum mechanically using an embedded cluster method, and compared with the results of Mott-Littleton (ML) calculations. We investigate the electron affinity and the orientation of CN^- ligands. The dependence of vibrational frequencies of the CN stretching mode on the ligand orientation, charge of the impurity and the relative position of the ligands and the charge compensating vacancies are calculated. Analysis of these results demonstrates the ability of ML calculations to predict the relative stability of different configurations of this particular family of defects. Comparison of the ML and embedded cluster calculations reveals the contributions to the defect energy and stability.