Structural Systematics and Topological Analysis of Coordination Polymers with Divalent Metals and a Glycine-Derived Tripodal Phosphonocarboxylate

Abstract

A novel family of four hybrid metal phosphonate coordination polymers is reported that are constructed from divalent metal ions (Ca, Sr, Ba, and Pb) and BPMGLY (bis-phosphonomethylglycine, a phosphonated derivative of glycine). These compounds (and their compositions) are Ca-BPMGLY (CaBPMGLY·H2O), Sr-BPMGLY (SrBPMGLY·H2O), Ba-BPMGLY (Ba3.5(BPMGLY)2·6H2O), and Pb-BPMGLY (PbBPMGLY·H2O). They were obtained by hydrothermal reactions in acidic aqueous solutions (pH range 2.3–5.7) and fully characterized by physicochemical methods and structural analysis. Ca-BPMGLY, Sr-BPMGLY, and Pb-BPMGLY have very similar 3D coordination polymer structures, and the latter two are isostructural. In contrast to the Ca, Sr, and Pb analogs, Ba-BPMGLY possesses a different 2D layered network. These four new compounds, together with our previously reported 2D coordination polymer Mg-BPMGLY (MgBPMGLY·2H2O, Demadis et al. Inorg. Chem. 2012, 51, 7889–7896), were topologically classified revealing (i) the uninodal 3-connected net with the hcb topology in Mg-BPMGLY, (ii) the uninodal 5-connected nets with the bnn and vbj topology in Ca-BPMGLY and Sr-BPMGLY, respectively, and (iii) the very complex topologically unique hexanodal 4,4,6,6,7,8-connected net in Ba-BPMGLY. The vbj topology was also identified in the related Pb-BPMGLY 3D framework. These topological features show that the complexity of BPMGLY-driven 2D and 3D metal–organic networks increases periodically following the Mg < Ca ≤ Sr ≪ Ba trend.