Syntheses Structures And Luminescent Properties Of Hg(â…¡) Complexes Based On O-pyridyl Imino

The Schiff–base ligands are applied widely in conctructing metal–organiccomplexes, which are owing to the facile preparation, structural varieties andvaried chemical properties. Simultaneously, the Schiff–base ligands are capable offorming complexes with certain transition–metal which can exhibit highthermodynamic stability, good fluorescent properties and biological activities, etc.So it is very important to design and synthesis the luminescent metal complexes ofHg（II） metal ion with Schiff–base ligands. In this paper, we have designed andsynthesized seven o-pyridine imino ligands and its Hg（II） complexes. Thestructures of these complexes were characterized by single crystal X–raydiffraction, IR spectra,1H NMR and elemental analysis. UV–Vis spectra,fluorescent emission spectra, fluorescence decay curves and fluorescent quantumyields are used to characterize their fluorescent properties.The reactions of pyridine-2-carboxaldehyde and a series of amines in organicsolvent gave the seven ligands （L^1L7）, and we obtained the singal crystals of L5and L6which are recrystallized from n-hexane and petroleum ether, respectively.The fluorescent properties of seven ligands have been characterized by UV–Visand emission spectra in CH₃OH. The results reveal that seven ligands （L^1L7）exhibit a sigal blue emission with the maximum at406,408,423,421,430,409and408nm, respectively, which is clearly assigned to the fluorescent emissionfrom the ligand–centered Ï€*â†'Ï€ transitions.Seven novel Hg（II） coordination complexes （1⁷） based on Schiff–basesligands （L^1L7） have been synthesized under solvothermal conditions. All Hg（II）complexes were obtained as crystals, the crystal structures were determined bysingle crystal X–ray diffraction. Structural study reveals that they are isostructuraland each center mercury adopts slightly distorted tetrahedron coordinationgeometry with one nitrogen donor from pyridine, one nitrogen donor from amineand two chlorine anions, respectively. In addition, there are a large number ofhydron bonds（C–H···Cl,4aslo has O–H···Cl） in their structures of1⁷, and theintermolecular weak interactions provides additional stability to the crystalstructures.We study their fluorescent properties in different polarity solvents（polarity:DMSO＞CH₃CN＞CH₃OH） by emission spectra and fluorescence decay curves.The results show that1⁷exhibit a red shift of emission spectra in DMSO andCH₃CN solvents with increasing solvent polarity, indicating a change in dipolemoment of1⁷upon excitation. However, there is a longest wavelength in CH₃OH, which originates CH₃OH solvent excites hydrogen bonds and can lead tostabilization of the excited state. The emission observed in different solvents of1⁷is assigned to the Ï€*â†'Ï€ intreligand fluorescence. The fluorescence decaycurves reval that the longest average life of1⁷is in the CH₃OH solventcomperared with in the DMSO and CH₃CN solvents, we conclude it is closelyrelated to hydron bonds effect in CH₃OH solvent. Their average life is8.25,6.35,8.03,10.72,9.44and10.87μs in CH₃OH solvent, respectively. The fluorescentquantum yield of5is much higher than other complexs, which is ascried that thedihedral angle of the planes in complex5is smallest one and the electro–donor ofp-methyl in5could avor to boost the fluidity of Ï€ electron.