Coordination complexes of Cd(II), Cu(II), Zn(II), and substituted diimide ligands: syntheses, structural analyses and gas sorption studies

We report the syntheses, structural and thermal analyses of four coordination complexes namely {[Cd(L1)2(NDC)]⸱4DMF}n (1), {[CuL2]⸱DMF}n (2), {[Zn(L3)0.5(DDN)]⸱DMF}n (3) and {[Zn(L4)0.5(DDN)]⸱DMF⸱H2O}n (4). Here, L1 is 2,2'-bis(pyridin-4-ylmethyl)-[5,5'-biisoindoline]-1,1',3,3'-tetraone; L2 is 2,2'-(1,1',3,3'-tetraoxo-[5,5'-biisoindoline]-2,2'-diyl)diacetic acid; L3 is 2,7-bis(pyridin-3-ylmethyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone; L4 is 2,7-bis(pyridin-4-ylmethyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone; DMF is N,N-dimethylformamide; H2NDC is 2,6-naphthalene dicarboxylic acid; and H₂DDN is 6,6'-dithiodinicotinic acid. Complexes 1, 3, and 4 are three-dimensional, while complex 2 is two-dimensional. Powder X-ray diffraction indicates that complex 1 changes its structure upon desolvation but does not revert to its original form when exposed to DMF. Carbon dioxide (CO2) sorption studies on 1 indicate that the complex adsorbs minimal amounts of CO2 at 273 K.