The geometry, frequency and intensity of the vibrational bands of 8-hydroxyquinoline (8-HOQ) were obtained by HF and density functional theory (DFT) with BLYP and B3LYP functionals and 6-31G(d) as the basis set. The optimized bond lengths and bond angles are in good agreement with the X-ray data. The vibrational spectra of 8-HOQ which is calculated by the HF and DFT methods, reproduces the vibrational wavenumbers and intensities with an accuracy, which allows reliable vibrational assignments. Complexes of the type Hg(8-HOQ)X-2 [where X = Cl, Br] have been studied in the 4000-200 cm(-1) region, and assignment of all the observed bands were made. The analysis of the infrared spectra indicates that there are some structure-spectra correlations. (C) 2004 Elsevier B.V. All rights reserved.