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

The preparation of five different compounds, [La2(H2pmd)3(H2O)12] (1: 1D), [La2(H2pmd)­(pmd)­(H2O)2] (2: 3D), [La­(H3pmd)­(H2pmd)­(H2O)] (3: 3D), [La2(H2pmd)3(H2O)2] (4: 3D), and [La2(H2pmd)­(pmd)­(H2O)4] (5: 3D), as crystalline materials from
the
reaction of 1,4-phenylenebis­(methylene)­diphosphonic acid (H4pmd) 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 min)
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 (1D) 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.