Structural diversity and fluorescent properties of Zn(ii)/Cd(ii) coordination polymers with a versatile tecton 2-(carboxymethoxy)benzoic acid and N-donor co-ligands

Abstract

Four novel Zn(II) and Cd(II) coordination polymers, {[Zn(cmb)(dpa)]·H₂O}_n (1), {[Zn(cmb)(bpp)]·2.5H₂O}_n (2), {[Zn(cmb)(bimb)]·3H₂O}_n (3), and {[Cd₂(cmb)₂(bimb)]·H₂O}_n (4) (H₂cmb = 2-(carboxymethoxy)benzoic acid; dpa = 4,4′-dipyridylamine; bpp = 1,3-di(4-bipy)propane; bimb = 1,4-bis(imidazol)butane), have been synthesized and characterized by elemental analysis, IR spectra, and X-ray diffraction. Complex 1 exhibits a diamond (dia) framework of four-fold interpenetration (class IIIa). 2 features a rare 1D → 3D polycatenated architecture, which is built from the interlocking of two sets of 1D supramolecular loops running in different directions (almost perpendicular). The 3D crystalline lattice of 3 is constructed through the parallel packing of corrugated 2D 4⁴ (sql) nets. Complex 4 shows a 2D network with the (3,4)-connected (4³)₂(4 × 10⁴ × 12)(4² × 10⁴) topology, which consists of 1D [Cd(cmb)]_n arrays and helical pillars. The results clearly indicate the importance of linking modes of organic ligands and metal centers as well as the auxiliary ligands in the direction of the diverse structures for complexes 1–4. Thermal stabilities and luminescent properties of complexes 1–4 have also been investigated.