Gas Adsorption and Magnetic Properties in Isostructural Ni(II), Mn(II), and Co(II) Coordination Polymers

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.