A series of mixed-ligand M(II) complexes containing 1,10-phenanthroline (phen) and 3-methylpyridine-2-carboxylic acid (3-mpaH) or 6-methylpyridine-2-carboxylic acid (6-mpaH), namely [Co(3-mpa)(2)(phen)]center dot 3H(2)O (1), [Hg(6-mpa)(2)(phen)]center dot 2H(2)O (2), [Mn(6-mpa)(2)(phen)]center dot 2H(2)O (3), [Co(6-mpa)(2)(phen)]center dot H2O (4) and [Ni(6-mpa)(2)(phen)]center dot H2O (5), were synthesized for the first time. Among them, 1 was obtained as single crystals. The structural characterization for 1 was conducted using X-ray diffraction and that for 2-5 using mass spectrometry. The IC50 values for alpha-glucosidase inhibition of 1-5 were obtained as 0.161 to >600 mu M. The spectral properties were also investigated using Fourier transform infrared and UV-visible spectra. Furthermore, to investigate the geometrical parameters, spectral and electronic properties and second- and third-order nonlinear optical parameters for 1-5, density functional calculations were applied.