Three novel Ho(III) complexes with different auxiliary ligands: Synthesis, crystal structures and thermal properties

Three novel Ho(III) complexes, [(Ho(2-Br-5-MOBA)3(terpy)(H2O)] (1), [Ho(2-Br-5-MOBA)3(2,2′-bipy)]2 (2) and [Ho(2-Br-5-MOBA)3(5,5′-DM-2,2′-bipy)]2 (3) (2-Br-5-MOBA = 2-bromine-5-methoxybenzoate, terpy = 2,2:6′,2″-terpyridine, 2,2′-bipy = 2,2′-bipyridine, 5,5′-DM-2,2′-bipy = 5,5′-dimethy-2,2′-bipyridine), have been synthesized and characterized by single-crystal X-ray diffraction. Although 1–3 have the same triclinic crystal system and P 1 ¯ space group, they show three different types of molecule structures. For 1, it is mononuclear and fake binuclear units constituted by the mononuclear molecules are stitched together via π–π stacking and C–H⋯O hydrogen bonding interactions to form the 1D, 2D supramolecular structure. Complexes 2 and 3 are binuclear structures with the different coordination numbers, which are assembled into 1D, 2D, 3D supramolecular structures by different intermolecular interactions. This is because of the different auxiliary ligands. The thermal decomposition mechanism of complexes 1–3 were studied by TG analysis and further authenticated by TG/DSC-FTIR techniques, indicating that the difference of the auxiliary ligand affects the thermal stabilities of complexes. The average molar heat capacity values of the complexes gradually increased with an increase of temperature, indicating the complexes have good thermal stability within this range of temperature. In addition, the IR, PXRD, and the antibacterial activities of complexes 1–3 were measured.