Hydrothermal syntheses, structures and characterizations of two luminescent cadmium(II) complexes with p-xylenediphosphonic acid and N-donor ligands

Two novel cadmium diphosphonates [Cd(cis-H4BDPP)(2,2′-bipy)2]·(trans-H2BDPP)]n (1) and [Cd(trans-H2BDPP)(phen)]n (2) (H4BDPP=p-xylenediphosphonic acid, phen=1,10-phenanthroline, 2,2′-bipy=2,2′-bipyridine) were hydrothermally synthesized from p-xylenediphosphonic acid and CdSO4·3H2O with phen or 2,2′-bipy as second ligand components and characterized by means of elemental analyses, IR, TG analysis, luminescence spectroscopy and single crystal X-ray diffraction. Compound 1 consists of a novel one-dimensional (1D) sinusoidal [Cd(cis-H4BDPP)(2,2′-bipy)2] chains and trans-H2BDPP anions. Compound 2 possesses a three-dimensional architecture built from double zigzag –Cd–O–P–O–Cd– chains pillared by trans-p-xylylenediphosphonate ligands from four different directions. There are hexagonal channels running along the c-axis and the coordinated phen ligands suspend in the hexagonal channels. The results indicate that p-xylenediphosphonic acid can adopt varied coordination modes and conformations in the formation of the complexes and the influence of the N-donor ligands on the structure of the complexes is discussed. - Graphical abstract: Two new cadmium diphosphonates were obtained by using two different auxiliary ligands. The influence of the N-donor ligands on the structure of the complexes is discussed. Highlights: ► The first example of cadmium(II)-p-xylenediphosphonates templated by second ligand. ► The role of size of the auxiliary ligand on the structure of cadmium p-xylenediphosphonates. ► The cis and trans configurations of p-xylenediphosphonates exist in the same crystal structure. ► Three-dimensional 4-connected framework with PtS network topology.