SYNTHESES, STRUCTURES AND PHYSICAL PROPERTIES OF SOME LANTHANIDE COMPLEXES AND ORGANIC SALTS

Abstract

Lanthanides are termed rare-earth elements; they are not rare in nature because their levels in the earth's crust are often equal to or higher than those of some physiologically significant elements. Although the members are very similar from a chemical point of view due to the shielding of 4f valence electrons by the completely filled 5s2 and 5p6 orbital but each of them has its own very specific physical properties including color, luminescent behavior and nuclear magnetic properties. Studies based on lanthanide ions are of special challenge due to their specific electronic, magnetic or spectroscopic properties result from a precise description of coordination sphere around the metal ions. Coordination compounds of lanthanides have found a variety of application in material science including contrast agents, superconductors, magnetic materials, catalyst and anticancer agents. Due to these attractive features, the coordination and supramolecular chemistry of lanthanide complexes have For the sake of convenience, the work embodied in the thesis is presented in the following chapter: The first chapter of the thesis is the general introduction and presents an up to date survey of literature related to the various lanthanide complexes, organic compounds (salts), their photophysical properties and thermal analysis respectively. The different types of complexes and salts related to the present research have been posed in the context of the cited work. Some pH dependent europium (III) and gadolinium (III) complexes viz., [Eu(phen)2Cl3CH3OH], [Eu(2,6-DNP)3phenCH3OH], [Eu(2,6-DNP)3phen(OH)].Hphen, [Eu (2,6-DNP)3bipyOH2], [Eu(2,6-DNP)3bipy(OH)].Hbipy, [Gd(phen)2(N03)2], [Gd(2,6-DNP)3 phenCH3OH], [Gd(2,6-DNP)3phen(OH)]2.(Hphen)2, [Gd(2,6-DNP)3bipyOH2], [Gd(DNP)3 bipy(OH)].Hbipy having 2,6-dinitrophenol (2,6-DNP), 1,10-phenanthroline (phen) and 2,2'- bipyridine (bipy) ligands have been synthesized and characterized by different physicochemical methods including single crystal X-ray crystallography are presented in chapter two. Their thermal properties have been studied by thermogravimetric analysis (TG) and demonstrated that the final product after decomposition was stable oxide (Eu203 and Gd203) for all these complexes. The thermal stability of these complexes decreases in the order: in [M(2,6-DNP)3phen(OH)].Hphen > [M(2,6-DNP)3bipy(OH)].Hbipy > [M(2,6-DNP)3phen CH3OH] > [M(2,6-DNP)3bipyOH2] > [Eu(phen)2Cl3CH3OH] / [Gd(phen)2(N03)3], (M = Eu, Gd). Isothermal thermogravimetric study in the range of 410-450 °C and 270-310 °C has been performed for Eu(III) and Gd(III) complexes respectively, while the kinetics of thermal decomposition was evaluated by applying model fitting as well as an isoconversional methods. To investigate the response of these complexes under the condition of rapid heating, ignition delay (Dj) has been measured. The third chapter of the thesis deals with the syntheses of some lanthanide [Ln(III) = Gd(III), Eu(III), Tb(III] complexes viz., [Gd(tptz)Cl2(OH2)4].C1.4H20, [Gd(tptz) (SCN)3(CH3OH)2OH2].CH3OH, [Gd(tptz)(OBz)2(u-OBz)OH2]2.H20, [Gd(phen)Cl2(OH2)4] .Cl.CH3OH, [Gd(phen)2(SCN)3CH3OH].phen, [OH2(phen)(2-pyca)2Gdi(u-ox)Gd2(2-pyca)2 (phen)OH2].6H20, [Eu(tptz)Cl3(CH3OH)2].CH3OH, [Eu(tptz)(SCN)3(CH3OH)2OH2].CH3OH, [OH2(OBz)2(tptz)Eu,(u-OBz)2Eu2(tptz)(OBz)2OH2].CH3OH.7H20, [Eu(phen)2(SCN)3CH3- -OHJ.phen, [OH2(phen)(2-pyca)2Eui(u-ox)Eu2(2-pyca)2(phen)OH2].6H20, [Tb(tptz)Cl3(CH3- -OH)2].CH3OH, [Tb(tptz)(SCN)3(CH3OH)2OH2].CH3OH, {[Tbi(tptz)(OBz)2(u-OBz)]2.[Tb2 (tptz)(OBz)3CH3OH]}.CH3OH.2H20, [Tb(phen)2Cl3OH2].CH3OH, [Tb(phen)2(SCN)3CH3- -OH].phen, [OH2(phen)(2-pyca)2Tb1((i-ox)Tb2(2-pyca)2(phen)OH2].6H20 where 2,4,6-tris(2- pyridyl)-1,3,5-triazine, 1,10-phenanthroline, K.SCN, sodium benzoate (NaOBz), 2-pyrazine carboxylic acid (2-pyca) act as supporting ligands. These complexes have been characterized by different methods including IR and single crystal X-ray crystallography. These complexes were tested for photophysical and thermal behavior. The complexes [Gd(tptz)(SCN)3(CH3OH)2OH2] .CH3OH, [Eu(tptz)(SCN)3(CH3OH)2OH2] .CH3OH, [Tb(tptz) (SCN)3(CH3OH)2OH2].CH3OH are mononuclear and show the three dimensional pseudo host- guest like supramolecular structure along 'c' axis. The same reaction in presence of sodium benzoate gave binuclear bridged complexes [Gd(tptz)(OBz)2(u-OBz)OH2]2.H20, [OH2(OBz)2(tptz)Eu1(^-OBz)2Eu2(tptz)(OBz)2OH2].CH3OH.7H20, {[Tb,(tptz)(OBz)2(n- OBz)]2.[Tb2(tptz)(OBz)3CH3OH]}.CH3OH.2H20. The photophysical properties of these complexes have been studied with ultraviolet absorption, excitation and emission spectral studies. Thermogravimetric analysis showed that after complete decomposition, all complexes resulted in the formation of thermally stable lanthanide oxide (Ln203). The chapter four of the thesis deals with the preparation of salts having picric acid [(OH)(N02)3C6H2] (PA) and nitrogen-rich heterocycles like different ditopic pyrazoles [PzH, IV PzMe2H, PzPhMeH, H2dmpz], 1,10-phenanthroline (phen), 2,2';6',2"-terpyridine (terpy), hexamethylenetetramine (hmta), 2,4,6-tris(2-pyridyl)-l,3,5-triazine (tptz), urea, 1H-1,2,4- triazole-3,5-diamine (guanazole), cyclohexane-l,2-diamine (1,2-DACH), 6-phenyl-l,3.5- triazine-2,4-diamine (benzoguanamine). The reaction of picric acid with other components resulted in the formation of various types of salts as [2PA".2PzH2+.OH2], [PA".PzMe2H2+], [PA" .PzphMeH2+.CH3OH], [2PA\2H2dmpzH+.CH3CN] [PA".phenH+.CH3OH], [2PA".terpyH2+2], [PA.hmta], [3PA".tptzH3+3], [PA'.Uronium], [PA".3,5-diamino-l,2,4-triazolium], [PA" .l/2cyclohexane-l,2-diaminium], [PA".6-phenyl-2,4-diamino-l,3,5-triazinium]. Due to presence of nitrogen-rich heterocycles, each salt contains infinite two or three dimensional structures held together by primary N-H—O, O-H—N, O-H—O hydrogen bonds and secondary C-H—O interactions. The structures and harmonic vibration frequencies of the complexes were calculated in terms of the density functional theory. The orientation of molecule remains same in both the solid and the gaseous phase. Theoretical studies suggested that the structures remain the same in both solid and gaseous phase, and the hydrogen bond interaction energy largely depends on the nitrogen-rich heterocycles in different salts. The thermal decomposition of these salts has been studied by thermogravimetry (TGA), derivative thermogravimetric (DTG) and differential thermal analysis (DTA). Kinetic parameters have been evaluated using models fitting and isoconversional methods. The material reagents, synthetic procedures, experimental details, theoretical calculation, ignition delay measurement, thermal kinetic analysis and different type of spectroscopic measurements are described in chapter five of the thesis. Methods for the preparation of different type complexes with Ln(III) and also synthesis of organic salt have been reported.