Synthesis of 4-Phosphonobutanesulfonic Acid and Systematic Investigation of Copper Phosphonatobutanesulfonates by High-Throughput Methods

The bifunctional linker 4-phosphonobutanesulfonic acid, H2O3P−C4H8−SO3H (H3L), was synthesized and characterized in detail and its use in the synthesis of new copper phosphonates was investigated. Thus, a high-throughput (HT) study was started for the systematic investigation of the system Cu(NO3)2/H3L/NaOH/H2O. An HT experiment comprising 48 individual hydrothermal reactions was performed to systematically investigate the influence of pH of the starting mixture as well as the molar ratio Cu2+:H3L. Two new compounds [Cu1.5(O3P−C4H8−SO3)(H2O)]·1.15H2O (1) and Cu2.5(O3P−C4H8−SO3)(OH)2 (2) were obtained. On the basis of scanning electron microscope images, the crystal sizes of both compounds were determined and a trend of the crystal size was established. The synthesis of both compounds was up-scaled in glass reactors by a factor of 10. While for 1 suitable single crystals for single-crystal diffraction measurement could be obtained, for 2 only multiple twinned crystals could be found. A structural model could be extracted, which was refined using Rietveld methods. Compound 1 contains a trimeric Cu3O12 cluster composed of two CuO5 and one CuO6 polyhedra. These trimers are connected by the -C4H8- group of the ligand to double layers, which are interconnected via hydrogen bonds to a three-dimensional framework. Compound 2 is built up from CuO6 polyhedra forming M-O-M layers. These layers are connected by the -C4H8- groups to a three-dimensional pillared framework. This leads to antiferromagnetic and ferromagnetic interactions at low temperatures for 1 and 2, respectively. In addition, the results of thermogravimetric investigations and IR spectra are also presented.