Two new isostructural 3D porous coordination polymers {[Ni2(DBIBA)3]·Cl·18H2O}n (1), {[Mn2(DBIBA)3]·Cl·3H2O}n (2) (DBIBA = 5-di(1H-benzo[d]imidazol-1-yl)benzoate) have been synthesized by acidic hydrolysis of cyanide functional group of 5-di(1H-benzo[d]imidazol-1-yl) benzonitrile under solvothermal conditions. Both the compounds have been characterized by X-ray crystallography, IR spectroscopy, thermogravimetry, powder X-ray diffraction, and elemental analysis. They form isoreticular structures with binodal 4,6-connected net having 1D hexagonal channels. These channels are occupied by water molecules. Frameworks are stabilized by hydrogen bonding interactions with anion and π–π interactions in the hexagonal cavity. Desolvated 1 exhibits selective CO2, while 2 shows N2, H2, and CO2 gas adsorption properties without any selectivity. This difference in gas adsorption properties is attributed to different degrees of flexibility of the framework. Magnetic susceptibility measurements at low temperature show weak ferromagnetic behavior in both coordination polymers 1 and 2 due to spin canting phenomenon. Complex {[Co2(DBIBA)3]·Cl·9H2O}n (3), which was previously reported by us, was also subjected to variable temperature magnetic susceptibility measurements.