Four alkaline earth metal complexes with structural diversities induced by cation size

Abstract

Studies concerning synthesis, structure and luminescence of four new alkaline earth metal complexes, namely, [Mg(H2O)6](L)2·2H2O (1), [Ca(L)2(H2O)3]n (2), [Sr(L)2(H2O)3]n (3) and [Ba(L)2(H2O)2]n (4) (L=1-carboxymethylpyridinium-4-carboxylate) are reported in detail. The results of X-ray crystallographic analysis reveal that 1 is a mononuclear complex with six coordinated water molecules, which further generate a 3D supramolecular structure consisting of two types of channels through delicate hydrogen bonds. While 2 and 3 are isostructural with 2D rhombic grid structure with (4, 4) topology, which are made up of heptacoordinated metal centers and L-shaped 2-connected organic linkers. As expected, with the increase of cation size, the structure of 4 is different from those of 2 and 3, which displays an undulated 2D network. Such 2D layers are composed of infinite 1D chains. The results indicate that the cation size, determining the geometry and coordination ability of metal centers, together with coordination mode and conformation of ligand L, have a subtle effect on the structural diversities. In addition, the solid luminescent properties of complexes 1–4 were also studied.