Lanthanide-organic Coordination Complexes Based On6,7-dihydropyrido(2,3-d)Pyridazine-5,8-dione:Synthesis,Characterization, Luminescence And Guest Sensing

Thesis contains two major parts:Part1. The hydrothermal reactions between tri-positive lanthanide cations and a pyridine derivative ligand6,7-dihydropyrido(2,3-d)pyridazine-5,8-dione (H2PDH), were proceeded for the development of four isostructural lanthanide-organic coordination complexes namely [Ln(HPDH)3(H2O)3].H2O (where Ln=Sm3+, Eu3+, Tb3+and Dy3+). The complexes were characterized by means of elemental analysis, powder XRD, TG-DTA, UV-vis and1R spectroscopy. Single crystal X-ray diffraction analysis indicate that the complexes form2-D layer structures which further form3-D supramolecular networks via hydrogen bondings and offset stacking (-H···π) interactions. Luminescence based sensing ability of partially dehydrated Tb(HPDH)3(H2O)3complex toward small solvents molecules along with its reusability has been studied. The sensing study of Tb(HPDH)3(H2O)3complex revealed that the nature of the solvents play key role in the enhancement or quenching of photoluminescence of the complexes, and isopropylalcohol (IPA) was found to be excellent sensitizer solvent while tetrahydrofuran (THF) as highly quenching solvent in this study and also both solvents show first order behavior to the photoluminescence intensity. It was found that the photoluminescence intensity of Tb(HPDH)3(H2O)3complex decreases with the increase of dielectric constant and normalized Dimroth-Reichardt ET parameter (ENT) values for protic solvents, while PL intensity increases with the increase of dielectric constant and (ENT) for dipolar aprotic solvents.Part2. The H2PDH ligand together with secondary ligand oxalic acid (H2OX) react with lanthanide(III) cations resulting in five isostructural lanthanide-organic complexes{[Ln(HPDH)(ox)(H2O)]}n,(where Ln=Eu3+, Tb3+, Sm3+ Gd3+) and {[(Dy)2(PDH)2(ox)(H2O)3]·H2O}n], under simple hydrothermal conditions. All complexes were characterized by means of elemental analysis, powder XRD, TG-DTA, UV-vis and IR spectroscopy. X-ray diffraction analysis were used for structural characterization of {[Eu(HPDH)(ox)(H2O)]}n,{[Tb(HPDH)(ox)(H2O)]}n and {[(Dy)2(PDH)2(ox)(H2O)3]·H2O}n complexes. These complexes are composed of2D layers, which further construct a3D supramolecular network. Each2D layer in {[Ln(HPDH)(ox)(H2O)]}n,[where Ln=Eu3+, Tb3+, Sm3+, Gd3+] complexes is composed of1D Eu-ox infinite chains, which are further connected by biconnected HPDH ligands, while each2D layer in complex {[(Dy)2(PDH)2(ox)(H2O)3]·H2O}n is formed by1D Eu-ox-H2O chains linked by bidentated PDH2-ligands. The singlet (1ππ*)(34,722cm-1) and triplet (3ππ*)(21,786cm-1) energy levels for the H2PDH ligand were calculated on the basis of UV-vis absorbance edges of free ligand and phosphorescence spectrum of {[Gd(HPDH)(ox)(H2O)]}n complex at77K, respectively. The luminescent properties and energy transfer mechanism of {[Eu(HPDH)(ox)(H2O)]}n,{[Tb(HPDH)(ox)(H2O)]}n,{[Sm(HPDH)(ox)(H2O)]}n and {[(Dy)2(PDH)2(ox)(H2O)3]·H2O}n complexes were investigated respectively. The {[Eu(HPDH)(ox)(H2O)]}n complex, was selected as a representative to examine its detecting and sensing potential toward organic solvent molecules in different laboratory solvents. The sensing potential of [Eu(HPDH)(ox)(H2O)]n complex for small molecules revealed that it can be used as sensing probe for ethanol and DMF, as ethanol was found to be an excellent sensitizer solvent while DMF as highly quenching solvent. Photoluminescence intensity of [Eu(HPDH)(ox)(H2O)]n complex decrease with the increase of dielectric constant, coordination ability and Dimroth-Reichardt ET parameter (ETN) values for polar protic solvents, while increase with the increase of dielectric constant, Dimroth-Reichardt ET values and coordination ability values for polar aprotic and nonpolar solvents. The [Eu(HPDH)(ox)(H2O)]n complex excellently regained its first photoluminescent intensity, revealing its reusability.