Five coordination networks based on zwitterionic ligands: synthesis, crystal structures and optical properties

Two flexible zwitterionic ligands of HL11 and HL22 derived from N-heteroaromatic molecules were used to construct five coordination polymers of [CdL11(H2O)2]·NO3·5H2O (1), [Zn(L11)2(H2O)4]·5H2O (2), [CdL11Cl] (3), [Zn(L22)2]·2H2O (4) and [Cd(L22)2] (5) by reaction with corresponding metal salts. In these compounds, L11 and L22 link up metal nodes to form distinct lamellar or linear coordination networks. Compounds 1 and 4 crystallize in chiral space groups, which are second-order non-linear optical (NLO) active induced by the asymmetric zwitterionic ligands and non-centrosymmetric metal coordination spheres. The distinct photoluminescent intensities of these coordination networks suggest that the framework structures play important roles on the electron transitions. This work illustrates that the utility of the zwitterionic ligands as connecting struts can generate some interesting solids as potential NLO and luminescent materials.