Structural Diversity of Lanthanum-Organic Frameworks Based on 1,4-Phenylenebis(methylene)diphosphonic Acid

Abstract

The preparation of five different compounds, [La-2(H(2)pmd)(3)(H2O)(12)] (1: ID), [La-2(H(2)pmd)(pmd)(H2O)(2)] (2: 3D), [La(H(3)pmd)(H(2)pmd)(H2O)] (3: 3D), [La-2(H(2)pmd)(3)(H2O)(2)] (4: 3D), and [La-2(H(2)pmd)(pmd)(H2O)(4)] (5: 3D), as crystalline materials from the reaction of 1,4-phenylenebis(methylene)diphosphonic acid (H(4)pmd) with lanthanum chloride is reported. Two different, fast, and economically viable synthetic approaches were employed with their various parameters being probed and, when possible, optimized to increase yields and purity: microwave-assisted synthesis (MWAS, in ca. 1 mm) and a bench procedure using standard ambient conditions (one-pot, ca. 10 min). Compounds 1 and 2 were isolated as phase pure crystalline materials. Compounds 3 and 4 were characterized by single-crystal X-ray diffraction from mixtures, and compound 5 was identified by powder X-ray diffraction studies (also from a physical mixture with 2). Structural details for all compounds were investigated by using in tandem X-ray diffraction (single-crystal and powder), electron microscopy (SEM and EDS), and FT-IR spectroscopy. Topological studies were also performed for all 3D networks. The conversion of compound 1 (ID) into 3D networks was investigated using hydrothermal, microwave, and one-pot methods: 1 was totally converted into phase-pure 2 via the hydrothermal method and one-pot method.