Three M(II)-squarate complexes, [Co(sq)(H2O)(Nmim)(4)] (1), [Zn(mu(1,3-)sq)(H2O)(2) (Nmim)(2)] (n) (2) and [Cd(mu(1,3-)sq)(H2O)(2)(Nmim)(2)] (n) (3) (sq = squarate, Nmim = N-methylimidazole) have been synthesized and characterized by elemental, spectral (IR and UV-Vis.) and thermal analyses. The molecular structures of the complexes have been investigated by single crystal X-ray diffraction technique. The squarate ligand acts as two different coordination modes as a monodentate (in 1) and bis(monodentate) (O (1-) O (3) ) bridging ligand (in 2, 3). The Co(II) atom has a distorted octahedral geometry with the basal plane comprised of three nitrogen atoms of Nmim ligands and a oxygen atom of squarate ligand. The axial position is occupied by a nitrogen atom of Nmim and one aqua ligand. The crystallographic analysis reveals that the crystal structures of 2 and 3 are one-dimensional linear chain polymers along the c and b axis, respectively. The configuration around each metal(II) ions are distorted octahedral geometry with two nitrogen atoms of trans-Nmim, two aqua ligands and two oxygen atoms of squarate-O-1,O-3 ligand. These chains are held together by the C-H center dot center dot center dot pi, pi center dot center dot center dot pi and hydrogen-bonding interactions, forming three-dimensional network.