Hyperfine coupling constants and the nature of the bonding has been studied by means of Density functional theory (DFT) calculations for a wide range of halogenide metal complexes of I, IV and V groups, halogen and interhalogen molecules and SO₃ complexes with ligands of different donor ability. DFT using various functional (BHandHLYP, B3LYP, B3PW91, OPTX, PBE) was employed. The calculated geometrical parameters, rotational constants and vibrational frequencies are in good agreement with the data of microwave spectroscopy in the gas phase. The DFT methods in conjunction with the all-electron basis set DGDZVP and with the zeroth-order regular approximation (ZORA) approximation for relativistic effects give good results in calculating constants of quadrupole interactions of halogen, nitrogen and metal atoms. For the first time the correlations between charge transfer and bond energies in SO₃ and halogen complexes were obtained. It has been shown that there exists difference between halogen and SO₃ complexes on one hand and metal halogenides on the other hand. From electron partitioning analyses and Klopman’s approximation it follows that for the metal and interhalogen complexes the electrostatic bonding is predominant while for SO₃ complexes there is a large contribution from covalent bonding.