In this study FT-IR spectra of M(L)(2)Ni(CN)(4) [where M = Fe or Zn, L = 4-aminopyridine) complexes are reported for the first time in the 400-4000 cm(-1) range. The spectral features suggest that the compounds are similar in structure to the Hofmann-type complexes with infinite polymeric layers formed with Ni(CN)(4)(-2) ions bridged by M(L)(2)(+2) cations. IR frequency shifts, upon formation of coordination compound are reliable indicators of the coordination mode of 4-aminopyridine. It is concluded that the ring nitrogen and not the amino nitrogen is involved in complex formation. In order to investigate metal-ligand coupling peculiarities, the vibrational wavenumbers of free and coordinated 4-aminopyridine have been calculated by a force field refinement method. The results indicated that the force field of free 4-aminopyridine should be altered in complex formation in order to represent the experimental data. (C) 2003 Elsevier Science B.V. All rights reserved.