Neutral mononuclear, dinuclear, tetranuclear d ~7/d ~(10) metal complexes containing bis-pyrazole/pyridine ligands supported by 2,6-bis(3-pyrazolyl)pyridine: Synthesis, structure, spectra, and catalytic activity

摘要

A series of novel bis-pyrazole/pyridine complexes, [Zn _2(HL ~1) _2(μ _2-SO _4)] _2· EtOH·H _2O (1), [Co _2(HL ~1) _2(μ _2-SO _4)] _2·2DMF· 6H _2O (2), [Zn _4(HL ~1) _4(μ _4-SO _4)][OH] _2 (3), [Zn _2(HL ~2) _2(μ _2-SO _4)] ·2H _2O (4), [Zn(H _2L ~2)(H _2O) _2](SO _4)·0.87H _2O (5) (H _2L ~1 = 2,6-di-(5-phenyl-1H-pyrazol-3-yl)pyridine, H _2L ~2 = 2,6-di-(5-methyl-1H-pyrazol-3-yl)pyridine), were synthesized hydrothermally from the self-assembly of Zn(II) or Co(II) with different types of bipyrazolyl/pyridine derivative ligands. All the complexes were characterized by elemental analysis, IR and UV-vis spectroscopy, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction. Structural analyses revealed that metal atoms (Zn and Co) in complexes 1-5 are five-coordination modes, forming slightly distorted trigonal bipyramidal geometries. In complexes 1-3, H _2L ~1 ligand connected the two metal centers via the tetradentate fashion, and the same form of connection was found in complex 4 with H _2L ~2 ligand. While in complex 5, H _2L ~2 only connected with one metal center via the tridentate fashion, which was different from those in complexes 1-4. Additionally, there are abundant hydrogen bonding interactions in complexes 1-4. Interestingly, for hydrogen bonding connecting fashions being different, the molecules for the complexes 1 and 4 are held together by the hydrogen bond to form a 1D supramolecular structure, whereas complexes 2 and 3 are a hydrogen bonded dimer. In addition, quantum chemical calculations for 1, 3, and 4, thermal behaviors and photoluminescent properties for 1 and 3-5 were performed and discussed in detail. In the mean time, we found that these complexes had potential catalytic activity for the oxidation reaction of cyclohexane.