A series of penta-coordinated CoII complexes of 1,4-diazacycloheptane (DACH) functionalized by additional imidazole or pyridine donor pendants, [CoL1Cl](ClO4)·H2O (1), [CoL2Cl](ClO4) (2) and [CoL3Cl](ClO4)·CH3OH (3), where L1=1,4-bis(imidazole-4-ylmethyl)-DACH, L2=1,4-bis(N-1-methylimidazol-2-ylmethyl)-DACH and L3=1,4-bis(pyridyl-2-ylmethyl)-DACH have been synthesized and characterized by elemental analyses, IR and UV–Vis spectra. In all the mononuclear complexes, each CoII center is penta-coordinated to four nitrogen donors of the ligand and one axial chloride anion. The crystal structure of complex 2 has been determined by X-ray diffraction analysis, which forms a one-dimensional linear structure through inter-molecular C–H⋯Cl and C–H⋯O hydrogen-bonding.