Self-assembly of a nonanuclear NiII cluster via atmospheric CO2 fixation: synthesis, structure, collision-induced dissociation mass spectrometry and magnetic property

A novel nonanuclear nickel(II) cluster identified as [Ni9(OH)6(CO3)2(ba)8(Hdmpz)6(DMF)2]•EtOH•2DMF (SD/Ni9a, Hba = benzoic acid, Hdmpz = 3,5-dimethyl-1H-pyrazole) is successfully constructed from mixed ligands. The single-crystal X-ray diffraction (SCXRD) structural analysis confirms the composition and reveals the “drum-like” inner core structure surrounded by ba- and DMF. Six Hdmpz ligands in its neutral form further sandwich the “drum” up and down and hydrogen-bonded with two carbonate anions which are derived from the atmospheric CO2 with the help of the base Et3N. Electrospray ionization mass spectrometry (ESI-MS) reveals the SD/Ni9a maintains intact core in solution with slightly exchange of outer ligands. Detailed collision-induced dissociation (CID) experiments reveal the collision energy (CE) promoted ligand losing and exchange between ba- and Hdmpz. Furthermore, the magnetic study shows that there is no interaction between the Ni centers at room temperature, whereas at low temperature the ferromagnetic coupling between the Ni centers is found with a S = 3 spin ground state of the cluster. Besides, UV-Vis spectrum and the photocurrent response measurements show its good optical properties with indirect band gap about 2.35 eV and fast current response upon visible light irradiation.