Investigations into the synthesis and fluorescence properties of Eu(III), Tb(III), Sm(III) and Gd(III) complexes of a novel bis-beta-diketone-type ligand

A novel bis-beta-diketon ligand, 1,1'-(2,6-bispyridyl)bis-3-phenyl-1,3-propane-dione (L), was designed and synthesized and its complexes with Eu(III), Tb(III), Sm(III) and Gd(III) ions were successfully prepared. The ligand and the corresponding metal complexes were characterized by elemental analysis, and infrared, mass and proton nuclear magnetic resonance spectroscopy. Analysis of the IR spectra suggested that each of the lanthanide metal ions coordinated to the ligand via the carbonyl oxygen atoms and the nitrogen atom of the pyridine ring. The fluorescence properties of these complexes in solid state were investigated and it was discovered that all of the lanthanide ions could be sensitized by the ligand (L) to some extent. In particular, the Tb(III) complex was an excellent green-emitter and would be a potential candidate material for applications in organic light-emitting devices (OLEDs) and medical diagnosis.     

Synthesis, characterization and fluorescence properties of novel pyridine dicarboxylic acid derivatives and corresponding Tb(III) complexes

Two novel ligands containing two pyridine-2,6-dicarboxylic acid conjugative units, 4-(2-(2,6-dicarbox-ypyridin-4-yl)vinyl)pyridine-2,6-dicarboxylic acid (L(1)) and 4-(4-(2-(2,6-dicarboxypyridin-4-yl)vinyl)styryl)pyridine-2,6-dicarboxylic acid (L(2)) and their complexes with Tb(III) have been synthesized and characterized by elemental analysis, IR spectra and NMR. The ligand synthetic route was optimized and the yield of ligands reached over 78% as a result of the Wittig-Horner reaction used. The fluorescent intensities of these complexes with corresponding complexes with single pyridine-2,6-dicarboxylic acid unit was compared. The result has shown that the ligands with two pyridine-2,6-dicarboxylic acid units are the excellent sensitizers to lanthanide fluorescence. Also, we investigated the fluorescence properties of these complexes in different solution and in different pH value. Due to their excellent green-emmiter, they would be a potential candidate material for applications in organic light-emitting devices and medical diagnosis.     

Synthesis of Eu(III) and Tb(III) complexes with novel pyridine dicarboxamide derivatives and their luminescence properties

A novel ligand, N2,N6-bis[2-(3-methylpyridyl)]pyridine-2,6-dicarboxamide (L2) and the corresponding Eu(III) and Tb(III) hydrochlorate complexes have been synthesized and characterized in detail based on elemental analysis, IR and NMR. The crystal and molecular structure of the complexes was determined by X-ray crystallography. The Eu(III) and Tb(III) ions were found to coordinate to the amido nitrogen atoms and pyridine nitrogen atoms. The luminescence properties of lanthanide complexes in solid state, in different solutions and in different pH value were investigated. The result shows that Tb(III) complexes exhibit more efficient luminescence than Eu(III) complexes, and the ligand (L2) is an excellent sensitizer to Tb(III) ion.     

Synthesis, characterization and luminescence property of N,N'-di(pyridine N-oxide-2-yl)pyridine-2,6-dicarboxamide and corresponding lanthanide (III) complexes

A new ligand, N,N'-di(pyridine N-oxide-2-yl)pyridine-2,6-dicarboxamide (LH2) and its several lanthanide (III) complexes (La, Eu, Gd, Tb, Y) were synthesized and characterized in detail based on elemental analysis, conductivity measurements, IR, 1H NMR, MS (FAB) and UV spectra and TG-DTA studies. The results indicated that the composition of these binary complexes is [Ln(LH2)(NO3)2.H2O]NO3.nH2O (n=0-1); while the ligand has a good planar structure with strong hydrogen bonds. The fluorescence spectra exhibits that the Tb (III) complex and the Eu (III) complex display characteristic metal-centered fluorescence in solid state while ligand fluorescence is completely quenched. However, the Tb (III) complex displays more effective luminescence than the Eu (III) complex, which is attributed to especial effectivity in transferring energy from the lowest triplet energy level of the ligands (T) onto the excited state (5D4) of Tb (III) than that (5D1) of Eu (III).     

Synthesis and infrared and fluorescence spectra of rare earth complexes with a novel amide-based ligand

A novel amide-based open-chain crown ether, N,N'-1,3-propanediyl-bis[2-(benzyl -carbamoyl-methoxy)-benzamide] (L) and its solid complexes with rare earth nitrates and picrates have been prepared. The complexes were characterized by elemental analyses, molar conductivity and IR spectra. The fluorescence properties of the Eu(III) and Tb(III) complexes in solid and in organic solvents were studied. Under the excitation of ultraviolet light, these complexes exhibit characteristic emission of europium and terbium ions. The results show that the ligand favor energy transfers to the emitting energy level of Tb(III). Some factors that influence the fluorescent intensity were also discussed.     

Synthesis of Eu(III) and Tb(III) complexes with novel pyridine dicarboxylic acid derivatives and their fluorescence properties

Starting from pyridine-2,6-dicarboxylic acid (DPA), a series of novel pyridine-2,6-dicarboxylic acid derivatives were synthesized. In these compounds, 4-(hydroxymethyl)pyridine-2,6-dicarboxylate (4-HMDPA) and 4-[(bis-carboxymethyl-amino)-methyl]-pyridine-2,6-dicarboxylic acid (4-BMDPA) were used as multifunctional ligands to coordinate with Tb(III) and Eu(III) and the complexes were prepared. The fluorescence properties of the solid complexes and their solutions were investigated in detail. The results indicated that the weak election-withdrawing group 4-hydroxymethyl in 4-position of pyridine in 4-HMDPA could weaken the fluorescence intensity of the lanthanide complexes. The contradistinctive experimental results showed that the fluorescence intensities of these complexes are related to pH values of the aqueous solutions and the dipole moments of solvent molecules: in the neutral aqueous solutions, the fluorescence intensities of these complexes were strongest, while the dipole moments were lower when the fluorescence intensities were stronger. 4-BMDPA is the better sensitizer and may be used as time-resolved fluoroimmunoassay. __________ Translated from Chemical Journal of Chinese Universities, 2006, 27(3) (in Chinese)     

New pyridine carboxamide ligands and their complexation to copper(II). X-Ray crystal structures of mono-, di, tri- and tetranuclear copper complexes

Seven new pyridine dicarboxamide ligands H2L(1-7) have been synthesised from condensation reactions involving pyridine-2,6-dicarboxylic acid (H2dipic), pyridine-2,6-dicarbonyl dichloride or 2,6-diaminopyridine with heterocyclic amine or carboxylic acid precursors. Crystallographic analyses of N,N'-bis(2-pyridyl)pyridine-2,6-dicarboxamide monohydrate (H2L8 x H2O), N,N'-bis[2-(2-pyridyl)methyl]pyridine-2,6-dicarboxamide and N,N'-bis[2-(2-pyridyl)ethyl]pyridine-2,6-dicarboxamide monohydrate revealed extensive intramolecular hydrogen bonding interactions. 2,6-Bis(pyrazine-2-carboxamido)pyridine (H2L6) and 2,6-bis(pyridine-2-carboxamido)pyridine (H2L7) reacted with copper(II) acetate monohydrate to give tricopper(II) complexes [Cu3(L)2(mu2-OAc)2]. X-Ray crystallography confirmed deprotonation of the amidic nitrogen atoms and that the (L6,7)2- ligands and acetate anions hold three copper(II) ions in approximately linear fashion. H2L8. Reacted with copper(II) tetrakis(pyridine) perchlorate to give [Cu(L8)(OH2)]2 x 2H2O, in which (L8)2- was tridentate through the nitrogen atoms of the central pyridine ring and the deprotonated carboxamide groups at one copper centre, with one of the terminal pyridyl rings coordinating to the other copper atom in the dimer. The corresponding reaction using H2L7 gave [Cu3(L7)2(py)2][ClO4]2, which transformed during an attempted recrystallisation from ethanol under aerobic conditions to a tetracopper(II) complex [Cu4(L7)2(L7-O)2].     

Calix[4]azacrowns as novel molecular scaffolds for the generation of visible and near-infrared lanthanide luminescence

Two calix[4]azacrowns, capped with two aminopolyamide bridges, were used as ligands for the complexation of lanthanide ions [Eu(III), Tb(III), Nd(III), Er(III), La(III)]. The formation of 1:2 and 1:1 complexes was observed, and stability constants, determined by UV absorption and fluorescence spectroscopy, were found to be generally on the order of log beta(11) approximately 5-6 and log beta(12) approximately 10. The structural changes of the ligands upon La(III) complexation were probed by 1H NMR spectroscopy. The two ligands were observed to have opposite fluorescence behaviors, namely, fluorescence enhancement (via blocking of photoinduced electron transfer from amine groups) or quenching (via lanthanide-chromophore interactions) upon metal ion complexation. Long-lived lanthanide luminescence was sensitized by excitation in the pi,pi band of the aromatic moieties of the ligands. The direct involvement of the antenna triplet state was demonstrated via quenching of the ligand phosphorescence by Tb(III). Generally, Eu(III) luminescence was weak (Phi(lum) 相似文献   

Luminescence of Eu3+ and Tb3+ Complexes of Two Macrobicyclic Ligands Derived from a Tetralactam Ring and a Chromophoric Antenna

Two macrobicyclic ligands derived from an 18‐membered tetralactam ring and 2,2′‐bipyridine or 2,6‐bis(pyrazol‐1‐yl)pyridine moieties, 1 and 2 , respectively, form stable complexes with Gd^III, Eu^III, and Tb^III ions in aqueous solution. The ligand‐based luminescence is retained in the Gd^III cryptates, whereas this radiative deactivation is quenched in the Eu^III and Tb^III cryptates by ligand‐to‐metal energy transfer, resulting in the usual metal‐centered emission spectra. Singlet‐ and triplet‐state energies, emission‐decay lifetimes, and luminescence yields were measured. [Tb⊂ 1 ]³⁺ cryptate shows a long luminescence lifetime (τ=1.12 ms) and a very high metal luminescence quantum yield (Φ=0.25) in comparison with those reported in the literature for Tb³⁺ complexes sensitized by a bipyridine chromophore. By comparison to [Ln⊂ 1 ]³⁺, [Ln⊂ 2 ]³⁺ presents markedly lower luminescence properties, due to worse interaction between the 2,6‐bis(pyrazol‐1‐yl)pyridine unit and the metal ion. Moreover, the luminescent metal and the triplet ligand energy levels of [Eu⊂ 2 ]³⁺ do not match. The effects of H₂O molecules coordinated to the metal centre and of thermally activated decay processes on nonradiative deactivation to the ground‐state are also reported.     

Syntheses, characterization, biological activity and fluorescence properties of bis-(salicylaldehyde)-1,3-propylenediimine Schiff base ligand and its lanthanide complexes

Eight new lanthanide metal complexes [LnL(NO(3))(2)]NO(3) {Ln(III) = Nd, Dy, Sm, Pr, Gd, Tb, La and Er, L = bis-(salicyladehyde)-1,3-propylenediimine Schiff base ligand} were prepared. These complexes were characterized by elemental analysis, thermogravimetric analysis (TGA), molar conductivity measurements and spectral studies ((1)H NMR, FT-IR, UV-vis, and luminescence). The Schiff base ligand coordinates to Ln(III) ion in a tetra-dentate manner through the phenolic oxygen and azomethine nitrogen atoms. The coordination number of eight is achieved by involving two bi-dentate nitrate groups in the coordination sphere. Sm, Tb and Dy complexes exhibit the characteristic luminescence emissions of the central metal ions attributed to efficient energy transfer from the ligand to the metal center. Most of the complexes exhibit antibacterial activity against a number of pathogenic bacteria.     

Low-temperature complexes of europium atoms and dimers with cyanophenylpyridines and alkylcyanophenylpyridines

It is shown by IR-Fourier and UV-visible spectroscopy that two biligand complexes of different stoichiometric composition Ln·2L and 2Ln·2L (Ln = Eu; L = 4-pentyl-4′-cyanophenylpyridine) are formed in the course of low-temperature co-condensation of metal and ligand vapors on the surfaces cooled with liquid nitrogen. Quantum-chemical modeling of the equilibrium structures of the mono-and binuclear complexes of europium with unsubstituted cyanophenylpyridyl and para-ethylcyanophenylpyridyl ligands was carried out. The main geometrical parameters of these compounds were determined. For mononuclear complexes, there is a competition between two mechanisms of coordination of the metal atom: formation of sandwich π complexes by interactions with the π orbitals of the aromatic ligand system and σ coordination at the nitrogen atoms of the pyridine ring. The sandwich structures of the binuclear complexes with 4-ethylcyanophenylpyridine are stabilized by N…H intermolecular contacts between the N atom of the cyano group and the terminal H atom of the ethyl group. The spectral shifts and the relative thermal stability of complexes with varying nuclearity are discussed.     

Simultaneous spectrophotometric determination of atrazine and cyanazine by chemometric methods

Three novel ligands containing pyridine-2,6-dicarboxylic acid unit, trans-4 -(4'-methoxystyryl) pyridine-2,6-dicarboxylic acid, trans-4-(4'-(dimethylamino)styryl)pyridine-2,6-dicarboxylic acid, and trans-4-(4'-(diphenylamino)styryl)pyridine-2,6-dicarboxylic acid were synthesized and their complexes with Eu(III), Tb(III) ions were successfully prepared. The ligands and the corresponding metal complexes were characterized by means of MS, elemental analysis, IR, (1)H NMR and TG-DTA. The luminescence spectra of Eu(III) and Tb(III) complexes in solid state were studied. The strong luminescence emitting peaks at 615 nm for Eu(III) and 545 nm for Tb(III) can be observed. The applications in cell imaging of the europium and terbium complexes were investigated.     

Synthesis, characterization and thermal behavior of 4-chloromethyl-2-(2-hydroxybenzilidenehydrazino) thiazole and its complexes with Cr(III), Co(II), Ni(II) and Cu(II)

A new ligand, 4-chloromethyl-2-(2-hydroxybenzilidenehydrazino) thiazole, has been synthesized from dicholoroacetone and 2-hydroxybenzylidenethiosemicarbazon. Metal complexes of the ligand were prepared from acetate salts of Co(II), Cu(II), Ni(II) and chloride of Cr(III) in dry acetone. Characterization of the ligand and its complexes was made by microanalyses, FT-IR, 13C, 1H NMR and UV-vis spectroscopy, magnetic susceptibility and thermogravimetric analysis. In the light of these results, it was suggested that two ligands coordinate to each metal atom by hydroxyl oxygen, imino nitrogen and thiazole ring nitrogen to form high spin octahedral complexes with Cr(III), Co(II), Ni(II) and Cu(II).     

Influence of ligand rigidity and ring substitution on the structural and electronic behavior of trivalent iron and gallium complexes with asymmetric tridentate ligands

Species 1-6 are [M(III)(L)2]ClO4 complexes formed with the PhO--CH=N-CH2-Py imines, (L(I))- and (L(tBuI))-, and PhO--CH2-NH-CH2-Py amines, (L(A))- and (L(tBuA))-, in which PhO- is a phenolate ring and Py is a pyridine ring and the prefix tBu indicates the presence of tertiary butyl groups occupying the positions 4 and 6 of the phenol ring. Monometallic species with d5 high-spin iron (1, 2, 3, 4) and d10 gallium (5, 6) were synthesized and characterized to assess the influence of the ligand rigidity and the presence of tertiary butyl-substituted phenol rings on their steric, electronic, and redox behavior. Characterization by elemental analysis, mass spectrometry, IR, UV-visible, and EPR spectroscopies, and electrochemistry has been performed, and complexes [FeIII(L(tBuI))2]ClO4 (2), [FeIII(L(tBuA))2]ClO4 (4), and [Ga(III)(L(tBuI))2]ClO4 (5) have been characterized by X-ray crystallography. The crystal structures show the imine ligands meridionally coordinated to the metal centers, whereas the amine ligands are coordinate in a facial mode. Cyclic voltammetry shows that the complexes with the ligands (L(tBuI))- and (L(tBuA))- were able to generate ligand-based phenoxyl radicals, whereas unsubstituted ligands displayed ill-defined redox processes. EPR spectroscopy supports high-spin configurations for the iron complexes. UV-visible spectra are dominated by charge-transfer phenomena, and imine compounds exhibit dramatic hyperchromism when compared to equivalent amines. The tertiary butyl groups on the phenolate ring enhance this trend. Detailed B3LYP/6-31G(d)-level calculations have been used to account for the results observed.     

Synthesis,Crystal structure and Fluorescence properties of a Binuclear Terbium(Iii) complex of N-(2-Pyridinyl)Ketoacetamide

A binuclear terbium(III) complex of N-(2-pyridinyl)ketoacetamide (HL) was synthesized and its crystal structure determined. Each terbium(III) binds to one N,O-bidentate HL, one O,O-bidentate L and two N,μ-O,O-tridentate bridging L ligands; the coordination polyhedron is a distorted square antiprism. The pyridine N and keto O atoms of the binucleating ligand are coordinated to each Tb with the amide O acting as a bridging atom. The adjacent [Tb₂(HL)₂L₄]²⁺ units are bridged by double C(R)NH…ONO₂…HN(R)C hydrogen bonds to form an infinite 1-D chain, and a 2-D layer structure results from a rare near face-to-face π,π-stacking interaction between the pyridine rings of the adjacent chains. The crystal structure analysis reveals that the ligands completely shield the Ln(III) ions. Excited by the absorption band at 370?nm, the Tb(III) complex displays characteristic metal-centered fluorescence while the ligand fluorescence is completely quenched, showing that efficient ligand-to-metal energy transfer (antenna effect) occurs.     

N-Tris[(2-aminoethyl)-2-(diphenylphosphoryl) acetamide)] — novel CMPO tripodand: synthesis,extraction studies and luminescent properties of lanthanide complexes

A ligand system containing three carbamoylmethylphosphine oxide (CMPO) moieties attached to a tripodal platform with a central nitrogen atom has been synthesized for metal complexation and extraction from neutral and nitric acid solutions. Liquid-liquid extractions performed for Ln(III), both from neutral and acidic media, show excellent extraction properties which exceeded those for the known mono- and di-CMPO derivatives as well as the related tripodands. A considerable enhancement of the D_Ln values was observed in the presence of IL ([bmim][Tf₂N]) in the organic phase towards lanthanide ions from 3M HNO₃ solutions. The protonation of the central amine nitrogen atom of the ligand 1 in the acidic media provides also the effective extraction of the perrhenate anionic complexes. The europium complexes formed by mono- and tris-CMPO ligands in the solid state, as well as Eu(III) and Tb(III) complexes generated in solutions, possess intensive luminescence at 300K     

Stabilization of calcium- and terbium-carboxylate bonds by NH...O hydrogen bonds in a mononuclear complex: a functional model of the active site of calcium-binding proteins

Novel benzoic acid ligands with bulky amide groups at the ortho position, 2,6-(MeCONH)(2)C(6)H(3)CO(2)H (1) and 2,6-(t-BuCONH)(2)C(6)H(3)CO(2)H (2), and their tris- and tetrakis(carboxylate) complexes with Ca(II) and Tb(III) ions, (NEt(4))(2)[Ca(II)[O(2)C-2,6-(t-BuCONH)(2)C(6)H(3)](4)] (4), [Tb[O(2)C-2,6-(t-BuNHCO)(2)C(6)H(3)](3)(H(2)O)(3)]] (5), and (NMe)(4)[Tb[O(2)C-2,6-(t-BuNHCO)(2)C(6)H(3)](4)(thf)] (6), were synthesized. The formation of the NH...O hydrogen bonds between the amide NH and carboxylate for 2, (NEt(4))[2,6-(t-BuCONH)(2)C(6)H(3)CO(2)] (3), and 4 was determined by (1)H NMR spectroscopy in solution and in the solid state (CRAMPS, IR). The ligand exchange reactions were attempted between 4 and a large excess of 2,4,6- Me(3)C(6)H(3)CO(2)H in chloroform-d solution; however, exchange reaction did not take place, indicating that the Ca(II) ions bound strongly to the carboxylate in 4. The Ca(II) ion binding properties with the benzoate derivatives were also examined using Tb(III) ion as a fluorescence probe. These results indicate that the NH...O hydrogen bonding between the amide NH and the oxygen atom of the carboxylate contributes to strong Ca(II) binding and prevents the dissociation of the calcium-carboxylate bond. The X-ray structural analyses of these complexes revealed that the NH.O hydrogen-bonded carboxylate ligands prefer the chelate-type coordination and create a mononuclear [Ca(O(2)CR)(4)](2)(-) or [Tb(O(2)CR)(4)](-) core with anionic charge, which is known only in the active site of calcium-binding proteins.     

Complexes of 2,6-bis[N-(2'-pyridylmethyl)carbamyl]pyridine: formation of mononuclear complexes, and self-assembly of double helical dinuclear and tetranuclear copper(II) and trinuclear nickel(II) complexes

The potentially pentadentate ligand 2,6-bis[N-(2'-pyridylmethyl)carbamyl]pyridine (H2L1), readily prepared from reaction of a diester of pyridine-2,6-dicarboxylic acid (H2dipic) and 2-aminomethylpyridine (ampy), shows limited tendency to form 1:1 M:L complexes with labile metal ions, although [CuL1] and [NiL1] were observed as minor species, the latter characterized by a crystal structure analysis. A mononuclear complex formed with inert Co(III) was characterized by a crystal structure as the neutral 1:2 complex [Co(L1)(HL1)] with two ligands acting as tridentate ligands, one coordinated by the central pyridine and its two flanking deprotonated amido groups, and the other by the central pyridine, one amido and one terminal pyridine group, with the remaining poorly coordinating protonated amide remaining unbound along with other terminal pyridine groups. Fe(III) is known to form a symmetrical 1:2 complex, but that complex is anionic due to binding of all four deprotonated amido groups; the unsymmetrical neutral Co(III) complex converts into a symmetrical anionic species only on heating for hours in aqueous base in the presence of activated carbon. The most remarkable tendency of H2L1, however, is towards the formation of robust double helical complexes: a dinuclear Cu(II) complex [Cu2L1(2)] forms, as well as a trinuclear Ni(II) complex [Ni(3)(L1)2(OAc)2(MeOH)2]. Moreover, in the presence of added H2dipic, the tetranuclear complex [Cu4(L1)2(dipic)2(OH2)2] is obtained. All helical complexes have been characterized by X-ray crystal structure analyses, and all crystals feature a racemic mixture of left- and right-handed double helices stabilized by inter-ligand pi-stacking (inter-ring distances of 3.2-3.8 A) of ligands which each span several metal ions. Using the chelating ligand pentane-2,4-dione (acac), each of the two pairs of adjacent monodentate ligands in [Ni3(L1)2(OAc)2(OH2)2] have been shown to be available for substitution without destroying the helical structure, to form [Ni3(L1)2(acac)2], also characterized by a crystal structure.     

Mixed ligand complexes of bis(phenylimine) Schiff base ligands incorporating pyridinium moiety Synthesis, characterization and antibacterial activity

The synthesis and structural characterization of mixed ligand complexes derived from 2,6-pyridinedicarboxaldehydebis(o-hydroxyphenylimine), 2,6-pyridinedicarboxaldehydebis(p-hydroxyphenylimine) (1(ry) ligands) and 2-aminopyridne (2(ry) ligand) are reported. The ligands and their transition metal complexes were characterized on the bases of their elemental analyses, IR, solid reflectance, magnetic moment, molar conductance and thermal analysis (TGA). The mixed ligand complexes are formed in the 1:1:1 (M:L(1) or L(2):L') ratio as found from the elemental analyses and found to have the formulae [MX(2)(L(1) or L(2))(L')].nH(2)O where M = Co(II), Ni(II), Cu(II) and Zn(II), L(1) = 2,6-pyridinedicarboxaldehydebis(p-hydroxyphenylimine), L(2) = 2,6-pyridine dicarboxaldehydebis(o-hydroxyphenylimine), L' = 2-aminopyridine, X = Cl(-) in case of Cu(II) complex and Br(-) in case of Co(II), Ni(II) and Zn(II) complexes and y = 0-3. The molar conductance data reveal that the chelates are non-electrolytes. IR spectra show that the Schiff bases are coordinated to the metal ions in a terdentate manner with NNN donor sites of the pyridine-N and two azomethine-N. While 2-aminopyridine coordinated to the metal ions via its pyridine-N. Magnetic and solid reflectance spectra are used to infer the coordinating capacity of the ligand and the geometrical structure of these complexes are found to be octahedral. The thermal behaviour of these chelates shows that the hydrated water molecules and the anions are removed in a successive two steps followed immediately by decomposition of the ligands (L(1), L(2) and L') in the subsequent steps. The activation thermodynamic parameters, such as, E*, DeltaH*, DeltaS* and DeltaG* are calculated from the TG curves and discussed. The ligands and their metal chelates have been screened for their antimicrobial activities and the findings have been reported, explained and compared with some known antibiotics.     

Syntheses,crystal structures,and luminescent properties of lanthanide complexes with tripodal ligands bearing benzimidazole and pyridine groups

Two tripodal ligands, bis(2-benzimidazolylmethyl)(2-pyridylmethyl)amine (L(1)) and bis(2-pyridylmethyl)(2-benzimidazolylmethyl)amine (L(2)), were synthesized. With the third chromophoric ligand antipyrine (Antipy), three series of lanthanide(III) complexes were prepared: [LnL(1)(Antipy)(3)](ClO(4))(3) (series A), [LnL(1)(Antipy)Cl(H(2)O)(2)]Cl(2)(H(2)O)(2) (series B), and [LnL(2)(NO(3))(3)] (series C). The nitrate salt of the free ligand H(2)L(1).(NO(3))(2) and six complexes were structurally characterized: Pr(3+)A, Y(3+)A, Eu(3+)B, Eu(3+)C, Gd(3+)C and Tb(3+)C, in which the two A and three C complexes are isomorphous. Crystallographic studies showed that tripodal ligands L(1) and L(2) exhibited a tripodal coordination mode and formed 1:1 complexes with all lanthanide metal ions. The coordination numbers of the lanthanide metal ions for the A, B, and C complexes were 7, 8, and 10, respectively. Conductivity studies on the B and C complexes in methanol showed that, in the former, the coordinated Cl(-) dissociated to give 3:1 electrolytes and, in the latter, two coordinated NO(3)(-) ions dissociated to give 2:1 electrolytes. Detailed photophysical studies have been performed on the free ligands and their Gd(III), Eu(III), and Tb(III) complexes in several solvents. The results show a wide range in the emission properties of the complexes, which could be rationalized in terms of the coordination situation, the (3)LC level of the complexes, and the subtle variations in the steric properties of the ligands. In particular the Eu(3+)A and Tb(3+)A complexes, in which the central metal ions were wholly coordinated by chromophoric ligands of one L(1) and three antipyrine molecules, had relatively higher emission quantum yields than their corresponding B and C complexes.