RESUMEN
Four new coordination polymers, including 1D, 2D and 3D structures, were synthesized via a hydrothermal method using Cd2+/Zn2+/Cu2+ metal salts as nodes. These polymers were formed through self-assembly of four different dicarboxylic acid ligands, namely adamantane-1,3-dicarboxylic acid (H2adc), glutaric acid (H2glu), 5-hydroxyisophthalic acid (H2hip) and fumaric acid (H2fum), in conjunction with the auxiliary ligand [1,4-bis(pyridin-4-ylmethyl)piperazine (bpmp). The corresponding formulae are [Cd3(adc)2(bpmp)Cl2(H2O)2]n (1), {[Cd2(glu)2(bpmp)2(H2O)2]·8H2O·2CH3OH}n (2), [Zn(hip)(bpmp)(H2O)]n (3) and [Cu(fum)(bpmp)(H2O)2]n (4). Single-crystal X-ray diffraction studies revealed that the Cd2+ centers in complex 1 all adopt a six-coordinate mode but two distinct {CdO2N2Cl2} and {CuO5Cl} units. The 3D network of complex 1 can be simplified to a binodal (4.6)-connected underlying net with the point symbol (3·42·5·62)4(32·62·72·88·10). Each Cd2+ cation in complex 2 adopts a seven-coordinate {CdO5N2} center, forming an asymmetric pentagonal bipyramidal coordination. Its stacking structure is formed by the interaction of hydrogen bonds between 2D supramolecular layers, with the adjacent layers exhibiting mirror symmetry. Each Zn2+ ion in complex 3 displays a {ZnO3N} four-coordinate unit. Its stacking structure is formed by one-dimensional [Zn(hip)(bpmp)(H2O)]n chains connected through hydrogen bonds. On the other hand, complex 4 features a Jahn-Teller distorted {CuO4N2} octahedral coordination. Subsequently, the thermal stability of these complexes was investigated. The solid-state fluorescence spectroscopy was employed to analyze complexes 1, 2 and 3. Additionally, a Hirshfeld surface analysis was performed on complex 3.
RESUMEN
A novel two-dimensional Co-MOF material {[Co(dptz)2(oba)2]·(DMF)2}n is prepared using mixed organic ligands, which exhibits both OER (oxygen evolution reaction) and HER (hydrogen evolution reaction) catalytic performance. The integration of an Fe dopant and amorphous interface into Co-MOF to improving the electrocatalytic performance of pristine MOFs (metal-organic frameworks) is demonstrated and the origin of the remarkable electrocatalytic performance of the catalyst is elucidated. The comprehensive characterization data of Fe@Co-MOFs illustrate that there is a crystallinity transition during the doping of Co-MOF, which increases the electron transfer rate of the material and ensures increased exposure of the ligand unsaturated active site on the surface, and modulates the electronic structure of the Co center in a synergistic manner. As a result, the optimized catalytic Fe@Co-MOF-3 with an amorphous structure exhibits outstanding electrocatalytic performance for the OER, with only 248 mV at a current density of 50 mA cm-2 and excellent stability after 11 h of testing in alkaline solution. Not only that, the HER was achieved with a low overpotential of 150 mV at 10 mA cm-2. The present work indicates that the as-synthesized Co-MOF and Fe@Co-MOFs offer prospects in developing electrocatalysts for water splitting.