Abstract
Three new copper coordination compounds derived from 2,2-bis(hydroxymethyl)propionic acid (dmpa) and hexamethylenetetramine (hmta) were obtained and their crystal structures were determined. The stoichiometry of the reagents applied in the syntheses reflects the metal to ligand molar ratio in the formed solid products. Due to the multiple coordination modes of the used ligands, wide structural diversity was achieved among synthesized compounds, i.e., mononuclear [Cu(dmp)2(hmta)2(H2O)] (1), dinuclear [Cu2(dmp)4(hmta)2] (2), and 1D coordination polymer [Cu2(dmp)4(hmta)]n (3). Their supramolecular structures are governed by O—H•••O and O—H•••N hydrogen bonds. The compounds were characterized in terms of absorption (UV-Vis and IR) and thermal properties. The relationships between structural features and properties were discussed in detail. Owing to discrepancies in the coordination mode of a dmp ligand, bidentate chelating in 1, and bidentate bridging in 2 and 3, there is a noticeable change in the position of the bands corresponding to the stretching vibrations of the carboxylate group in the IR spectra. The differences in the structures of the compounds are also reflected in the nature and position of the UV-Vis absorption maxima, which are located at lower wavelengths for 1.
Highlights
Coordination compounds have attracted interest, because of their different topologies and properties and due to their varied applications
The weaker coordination bonds of chelating dmp anions are ca. 1 Å longer than the stronger bonds. Despite their relatively greater length, they are binding in character, which was confirmed by natural bond orbital (NBO) analysis and an electron density map (Figure S1)
The copper(II) 2,2-bis(hydroxymethyl)propionate was not isolated from the solution after its synthesis, because it would have to be dissolved in water one more time before reaction with hmta
Summary
Coordination compounds have attracted interest, because of their different topologies and properties and due to their varied applications. Since the structure has a large impact on the exhibited properties, coordination compounds, especially coordination polymers and metal–organic frameworks, have become a focus of research in the field of crystal engineering [1]. The ability to control the way the molecules are ordered in the solid state could control exhibited properties. In this field, much has been achieved regarding the usage of organic linker ligands to design compounds capable of the absorbtion of gases [4,5], separation of compounds [6,7], or acting as effective catalyst [8,9,10]. The tuneable position of the coordinating groups in these organic spacers enables adequate control over the topology and dimensionality of the resulting networks
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