Flexible Ligands and Structural Diversity: Isomerism in Cd(NO₃)₂ Coordination Polymers

The ligands 1,4-bis(2-pyridylmethylsulfanylmethyl)benzene (L1) and 2,5-bis(2-pyridylmethylsulfanylmethyl)pyrazine (L2) were treated with Cd(NO3)2·4H2O in metal-to-ligand ratios of 1:1 and 2:1, respectively; L2 was also treated with CdCl2·2.5H2O in a 2:1 ratio. All products were found to be coordination polymers. The crystal structures of {[Cd(L1)(NO3)2]·CH2Cl2}∞ (1a), {[Cd(L1)(NO3)2]·4/3CH3CN}∞ (1b), {[Cd2(L2)(NO3)4]·2CH3CN}∞ (2·2CH3CN), and {[Cd2(L2)Cl4]·2CH2Cl2}∞ (3·2CH2Cl2) were determined. Compounds 1a and 1b were found to be conformational supramolecular isomers. The structure of 1b displayed topological isomerism with two isomeric polymer chains, 1b(1) and 1b(2), in the one crystal forming a single supramolecular array. The structure of 2·2CH3CN showed Cd2(L2) units linked together by nitrates bridging between the Cd(II) centers in a mode previously not seen in Cd(II) compounds. The overall structure of 3·2CH2Cl2 was found to be similar to that of 2·2CH3CN despite the presence of different anions and solvent molecules. Powder X-ray diffraction was used to investigate the nature of bulk preparations of compounds 1-3.