Synthesis and characterization of four new metal 5-phosphonoisophthalates discovered by high-throughput experimentation

A new ligand, 5-diethylphosphonoisophthalic acid ((HOOC)2C6H3-PO3(C2H5)2, H2Et2L), for the hydrothermal synthesis of inorganic-organic hybrid compounds was prepared and characterized by NMR-spectroscopy. Its in situ hydrolysis leads to the corresponding 5-phosphonoisophthalic acid ((HOOC)2C6H3-PO3H2, H4L). Applying high-throughput methods, different di- and trivalent metal salts for the synthesis of crystalline metal phosphonates based on H2Et2L have been screened. From the resulting discovery library, single-crystals of four new compounds, [Sm2(H2O)4(H(OOC)2C6H3-PO3)2].2H2O (1), [Cu3(H2O)(H(OOC)2C6H3-PO3)2].2H2O (2), Ca2(H2O)[H(OOC)2C6H3-PO3H]2 (3), and Ba2(H2O)3(OOC)2C6H3-PO3 (4), have been isolated. The single-crystal structure determination of the title compounds shows H4L to be a versatile ligand, exhibiting different types of coordination modes between the functional groups and the metal ions. A comparison of the structural features of the title compounds shows a varying degree of M-O-M connectivities. Thus, isolated metal-oxygen clusters (compounds 1 and 2), infinite M-O-M chains (compound 3), and infinite M-O-M layers (compound 4) are observed. The title compounds 1, 2, and 3 were further characterized by IR-spectroscopy, TG-, EDX-, and elemental chemical analysis. - Graphical abstract: Applying high-throughput methods, the new ligand 5-diethylphosphonoisophtalic acid, (HOOC)2C6H3-PO3(C2H5)2 (H2Et2L), was reacted with several di- and trivalent metal salts under hydrothermal conditions. Single-crystals of four new inorganic-organic hybrid compounds were isolated from the discovery library. The single-crystal structure analysis shows a varying M-O-M connectivity