Studies On Syntheses, Characterization, And Luminescent Properties Of Zinc(Ⅱ) Complexes With Schiff Ligands Containing 7-Amino-2, 4-dimethylquinolyl

The zinc(II) provides various types of chelate complex because of its versatility towards different kinds of ligands and its flexibility towards coordination number, ranging from three to six. Among these complexes, some have especially attracted attention as model compounds for the active sites of zinc-containing enzymes, as catalysts for the copolymerization of CO2 with epoxides, coupling reactions, oxidation reaction and Aldol reaction and as luminescent materials for organic light-emitting diodes. Zinc(II) complexes as luminescent materials have some advantage such as low cost, easy preparation, and the zinc(II) is spectroscopically silent. Quinoline is an important scaffold in the framework of various pharmacologi -cally active compounds including many with antimalarial, antibacterial, anti- inflammatory and antiasthmatic activities. Meanwhile some quinolines compounds have good luminescent properties and can be as sensors for the detection of metal ions. In this paper, we researched the self-assembly and the luminescent response of 7-amino-2,4-dimethyl quinoline with/to different acid. We have designed and synthesized two series of seven Schiff ligands with 7-amino-2,4-dimethylquinolyl. The luminescent properties of zinc(II) complexes with those Schiff ligands have been researched. Meanwhile we found a new method to synthesize acridine and its derivatives from the reaction of anilido-imine compounds with ZnCl₂.We found a simple and efficient method to synthesize 7-amino-2,4-dimethyl quinoline. X-ray diffraction analysis indicates that 7-amino-2,4-dimethylquinoline can form different supramolecular net-work structures with hydrogen chloride, formic acid and acetic acid, and the nitrogen atom in the quinoline ring is protonated. 7-Amino-2,4-dimethylquinoline produces blue fluorescence in both solution and the solid state. The maximum emission wavelengths of the three salts of 7-amino- 2,4-dimethylquinoline are similar in ethanol solution while different in the solid state, which is relative to the distance ofπ–πinteraction in the solid state, indicating that 7-amino- 2,4-dimethylquinolinum has luminescent response to anion in the solid state.Our research results also indicate that the new salicylaldiminato conjugated ligands are well suited for synthesizing the bissalicylaldiminato zinc complexes ( (Ar¹N=HCAr²O)₂Zn (Ar1 = 7-(2,4-Me₂)C₉H₄N, Ar² = C₆H₄ (S¹Zn); Ar¹ = 7-(2,4-Me₂)C₉H₄N, Ar² = 3,5-t-Bu₂C₆H₃ (S₂Zn); Ar¹ = 7-(2,4-Me₂)C₉H₄N, Ar² = 5-BrC₆H₄ (S3Zn); Ar¹ = 7-(2,4-Me₂)C₉H₄N, Ar² = 3,5-Br₂C₆H₃ (S4Zn) by alkane elimination reaction of ZnEt2 with corresponding ligands at room temperature. The crystal structures of complexes S1Zn and S2Zn were determined by X-ray diffraction analysis. The quinolyl rings with the same numberings in the adjacent two molecules are parallel withπ–πstacking interaction forming antiparallel dimer structures. The two six-membered chelating ring in these complexes are nearly perpendicular to each other. These new complexes produce bright fluorescence in both solution and the solid state, and the emission color in solution can be tuned by the 3,5- substituents on the salicylidene rings of the ligands. The quantum yields of these compounds are dependent on the elctron-donating abilities of the 3,5- substituents on the salicylidene rings of the ligands.We prepared three new anilido-imine ligands with 7-amino-2,4-dimethyl- quinolyl (ortho-C₆H₄(NHAr')(CH=NAr") [Ar' = 7-(2,4-Me₂)C₉H₄N, Ar"- = 2,6-Me₂C₆H₃ (2a); Ar' = 7-(2,4-Me₂)C₉H₄N, Ar" = 2,6-Et₂C₆H₃ (2b); Ar' = 7-(2,4-Me₂)C₉H₄N, Ar" = 2,6-iPr₂C₆H₃ (2c)] and four monoethyl zinc complexes with anilido-imine ligands ([ortho-C₆H₄(NHAr')(CH=NAr")]ZnEt [Ar' = 7-(2,4-Me₂)C₉H₄N, Ar" = 2,6-Me₂C₆H₃ (3a); Ar' = 7-(2,4-Me₂)C₉H₄N, Ar" = 2,6-Et₂C₆H₃ (3b); Ar' = 7-(2,4-Me₂)C₉H₄N, Ar" = 2,6-iPr₂C₆H₃ (3c); Ar' = 2,6-Me₂C₆H₃, Ar" = 2,6-iPr₂C₆H₃ (3d)]). There are only intramolecular N–H…N hydrogen bonds in the crystal structures of ligands 2b and 2c, while there are both intramolecular N–H…N hydrogen bond and weak intermolecular C–H…N hydrogen bond to form an infinite one-dimension chain in the crystal structure of ligand 2a for the lower steric interaction of methyl. The X-ray analysis reveals that complexes 3b and 3c exist in dimeric form with the N atom in–(2,4-Me2)C9H4N group coordinating to the Zn atom in another molecule. These complexes produce bright fluorescence in both solution and the solid state. The emission color in solution can be tuned by the ortho substituents on and the size of the rotatable aryl rings of the ligands. These complexes are air- and/or moisture- sensitive and can react with trace H2O and O2. We have obtained the crystals of the hydrolysis product of 3a and the oxidation product of 3d, being pentanuclear zinc complexes (3a') with hydroxy bridge and dinuclear zinc complexes (3d') with methoxy bridge, respectively.We unexpectedly found a new method to synthesize acridine and its derivatives when using anilido-imine and ZnCl₂ to synthesize the anilido-imine zinc chloride by lithium elimilation. The anilido-imine with no substituents on the ortho-position of anilido aromatic ring (ortho-C₆H₄(NHAr')(CH=NAr") can react with ZnCl₂ to form products with ring-closure. We have synthesized acridine and 2,4-dimethyl-benzo[j] [1,7]phenanthroline (h1) using this method. The NMR spectroscopy and crystal structures of acridine and h1 further confirm that the new method for the syntheses of acridine and its derivatives is feasible. 2,4-Dimethyl-benzo[j][1,7]phenanthroline exihibit blue fluorescence in both hexane solution and the solid state.