Aromatic Carboxylate Ligands Research Articles

Highly Luminescent and Thermally Stable Lanthanide Coordination Polymers Designed from 4-(Dipyridin-2-yl)aminobenzoate: Efficient Energy Transfer from Tb3+ to Eu3+ in a Mixed Lanthanide Coordination Compound

Herein, a new aromatic carboxylate ligand, namely, 4-(dipyridin-2-yl)aminobenzoic acid (HL), has been designed and employed for the construction of a series of lanthanide complexes (Eu(3+) = 1, Tb(3+) = 2, and Gd(3+) = 3). Complexes of 1 and 2 were structurally authenticated by single-crystal X-ray diffraction and were found to exist as infinite 1D coordination polymers with the general formulas {[Eu(L)(3)(H(2)O)(2)]}(n) (1) and {[Tb(L)(3)(H(2)O)].(H(2)O)}(n) (2). Both compounds crystallize in monoclinic space group C2/c. The photophysical properties demonstrated that the developed 4-(dipyridin-2-yl)aminobenzoate ligand is well suited for the sensitization of Tb(3+) emission (Φ(overall) = 64%) thanks to the favorable position of the triplet state ((3)ππ*) of the ligand [the energy difference between the triplet state of the ligand and the excited state of Tb(3+) (ΔE) = (3)ππ* - (5)D(4) = 3197 cm(-1)], as investigated in the Gd(3+) complex. On the other hand, the corresponding Eu(3+) complex shows weak luminescence efficiency (Φ(overall) = 7%) due to poor matching of the triplet state of the ligand with that of the emissive excited states of the metal ion (ΔE = (3)ππ* - (5)D(0) = 6447 cm(-1)). Furthermore, in the present work, a mixed lanthanide system featuring Eu(3+) and Tb(3+) ions with the general formula {[Eu(0.5)Tb(0.5)(L)(3)(H(2)O)(2)]}(n) (4) was also synthesized, and the luminescent properties were evaluated and compared with those of the analogous single-lanthanide-ion systems (1 and 2). The lifetime measurements for 4 strongly support the premise that efficient energy transfer occurs between Tb(3+) and Eu(3+) in a mixed lanthanide system (η = 86%).

Coordination Polymers with Bulky Bis(imidazole) and Aromatic Carboxylate Ligands: Diversity in Metal-Containing Nodes and Three-Dimensional Net Topologies

Five new three-dimensional transition metal coordination polymers (CPs) with dia and different aromatic carboxylates, [Cd(oba)(dia)0.5] (1), [Cd(Hbtc)(dia)]·3H2O (2), and [M3(2-stp)2(dia)6(H2O)2] (3a, M = Cd; 3b, M = Co; 3c, M = Ni) were synthesized under hydrothermal condition (dia = 9,10-di(1H-imidazol-1-yl)anthracene; oba = 4,4′-oxybis(benzoate); btc = benzene-1,3,5-tricarboxylate; 2-stp = 2-sulfoterephthalate). Compounds 3a–c are isostructural. The coordination geometries at cadmium in 1, 2, and 3a are capped trigonal prism, pentagonal bipyramid, and octahedron, respectively. This diversity in coordination geometry is in sharp contrast to 3c and previously reported nickel complexes of a similar ligand set. The difference in metal-containing node geometries and carboxylate structures results in diverse network connectivity, including a tcs topology for 1, an unprecedented binodal topology of (42.63.85)(42.6) for 2, and a rare trinodal topology of (4.64.8)2(43.63)2(44.610.8) for 3. Based on secondary building units, the networks in 2 and 3 can be, alternatively, described as rob and pcu (or ilc) nets, respectively. This work shows the effect of the specific ion and the rich potential of using bulky bis(imidazole) and aromatic carboxylate as ligands in the construction of CPs with unusual topologies.

A Series of Ca(II) or Ba(II) Inorganic–Organic Hybrid Frameworks Based on Aromatic Polycarboxylate Ligands with the Inorganic M–O–M (M = Ca, Ba) Connectivity from 1D to 3D

Solvothermal reactions of Ca(NO3)2 or Ba(NO3)2 with aromatic carboxylate ligands afforded four new inorganic–organic hybrid frameworks, [Ca(PBDC)(H2O)3]n (1), [Ca(OBDC)(H2O)]n (2), [Ba5(OBDC)4(H2O)2(NO3)2]n (3), and [Ba3(BTC)2(H2O)4]n (4) (H2PBDC = terephthalic acid, H2OBDC = phthalic acid, H3BTC = 1,3,5-benzenetricarboxylic acid). These compounds have been fully characterized by single crystal X-ray diffraction, powder X-ray diffraction, satisfactory elemental analysis, IR spectra, and TG analysis. X-ray analysis shows that compound 1 features a one-dimensional chain (1D) structure with the I1O0 connectivity, both compound 2 and compound 3 feature a two-dimensional (2D) layer structure with the I1O1 connectivity, I2O0 connectivity, respectively, compound 4 features a three-dimensional (3D) framework with a rare I3O0 connectivity. Thermal stabilities and luminescent properties of compounds 1–4 and NLO property of compound 4 have also been investigated.

A series of lanthanide compounds based on mixed aromatic carboxylate ligands: Syntheses, crystal structures and luminescent properties

Abstract A series of lanthanide complexes, [LnL1L21/2(H2O)2]n [Ln = La(1), Sm(2), Gd(3), Eu(4), H2L1 = 2,4-bis(4-methylbenzoyl)isophthalic acid and H2L2 = 2,5-bis(4-methylbenzoyl)terephthalic acid] have been prepared under hydrothermal conditions and characterized by PXRD, IR, elemental analysis and single crystal X-ray diffraction. Complexes 1–4 are isostructural and comprise paddlewheel dinuclear lanthanide secondary building units linked by four carboxylic groups. L1 ligands link the dinuclear lanthanide building blocks to form one-dimensional double-stranded looplike chains. The chains are further connected together to form two-dimensional layers by L2. Furthermore, the luminescent properties of 2 and 4 were also studied.

Synthesis, crystal structure and photophysical properties of lanthanide coordination polymers of 4-[4-(9H-carbazol-9-yl)butoxy]benzoate: the effect of bidentate nitrogen donors on luminescence

A new aromatic carboxylate ligand, 4-[4-(9H-carbazol-9-yl)butoxy]benzoic acid (HL), has been synthesized by the replacement of the hydroxyl hydrogen of 4-hydroxy benzoic acid with a 9-butyl-9H-carbazole moiety. The anion derived from HL has been used for the support of a series of lanthanide coordination compounds [Ln = Eu (1), Gd (2) and Tb (3)]. The new lanthanide complexes have been characterized by a variety of spectroscopic techniques. Complex 3 was structurally authenticated by single-crystal X-ray diffraction and found to exist as a solvent-free 1D coordination polymer with the formula [Tb(L)(3)](n). The structural data reveal that the terbium atoms in compound 3 reside in an octahedral ligand environment that is somewhat unusual for a lanthanide. It is interesting to note that each carboxylate group exhibits only a bridging-bidentate mode, with a complete lack of more complex connectivities that are commonly observed for extended lanthanide-containing solid-state structures. Examination of the packing diagram for revealed the existence of two-dimensional molecular arrays held together by means of CH-π interactions. Aromatic carboxylates of the lanthanides are known to exhibit highly efficient luminescence, thus offering the promise of applicability as optical devices. However, due to difficulties that arise on account of their polymeric nature, their practical application is somewhat limited. Accordingly, synthetic routes to discrete molecular species are highly desirable. For this purpose, a series of ternary lanthanide complexes was designed, synthesized and characterized, namely [Eu(L)(3)(phen)] (4), [Eu(L)(3)(tmphen)] (5), [Tb(L)(3)(phen)] (6) and [Tb(L)(3)(tmphen)] (7) (phen = 1,10-phenanthroline and tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline). The photophysical properties of the foregoing complexes in the solid state at room temperature have been investigated. The quantum yields of the ternary complexes 4 (9.65%), 5 (21.00%), 6 (14.07%) and 7 (32.42%), were found to be significantly enhanced in the presence of bidentate nitrogen donors when compared with those of the corresponding binary compounds 1 (0.11%) and 3 (1.45%). Presumably this is due to effective energy transfer from the ancillary ligands.

Syntheses, structures, and luminescent properties of three novel two-dimensional lanthanide coordination polymers with mixed aromatic carboxylate ligands

Three novel two–dimensional (2–D) coordination polymers {[Ln (bpdc) (BDC)0.5 (DMF) (H2O)]·1.5H2O}n [Ln = Tb (1), Sm (2), Gd (3); H2bpdc = 2,4′–biphenyldicarboxylic acid; H2BDC = 1,4–benzenedicarboxylic acid, and DMF = N,N′–dimethylformamide] have been successfully synthesized by the reactions of metal source Ln(NO3)2·5H2O with mixed aromatic carboxylate ligands named, H2bpdc and H2BDC in the mixed solution of DMF and H2O. Complexes 1–3 were characterized by element analyses, IR spectroscopy and single–crystal X–ray diffraction. The results reveal that three complexes are isostructural. In the molecular structure of 1, the neighboring Tb3+ cations are connected by the edge sharing fashion from two three-bridging μ3–oxygen atoms to construct a dinuclear polyhedron. The adjacent dinuclear units are linked by two bpdc2– ligands to form an infinite double zigzag chain containing quadrangular grids. These chains are linked by BDC2–, which acted as pillar to form a 2-D layered structure containing (4, 4) networks. The solid–state luminescent properties of complexes 1 and 2 were investigated at room temperature. Complexes 1 and 2 have displayed their characteristic emissions and decay lifetimes.

Synthesis, Crystal Structure, and Fluorescent Property of A Chiral 2D Polymer Based on Bis(2‐benzimidazoles) and Aromatic Carboxylate Ligands

AbstractWe have synthesized a new complex [Zn(H2C3PIm)(BTC)H2O]n (1) [H3BTC = 1,3,5‐benzenetricarboxylic acid, H2C3PIm = 2,2′‐(1,3‐propanediyl)‐bis(1H‐benzimidazole)] and determined its structure (C26H20N4O7Zn, Mr = 565.83) using single‐crystal X‐ray diffraction analysis. The complex crystallizes in the monoclinic system, space group P2(1) with a = 8.497(5), b = 16.316(5), c = 9.316(5) Å, β = 104.955(5), V = 1247.8(11) Å3, Z = 2, Dc = 1.506 g·cm–3, μ(Mo‐Kα) = 1.038 mm–1, F(000) = 580, S = 0.755, the final indices are R = 0.0386 and wR = 0.0456 for 3461 reflections with I > 2σ(I). In the asymmetric unit of complex 1, the distorted tetrahedral ZnII ion is bridged by the carboxylic oxygen atoms of the BTC ligand and the nitrogen atoms of the H2C3PIm ligand. The complex units are linked through BTC ligands into a chiral 2D layer and further connected into a 3D framework by π–π packing interactions between the adjacent H2C3PIm ligands. The complex exhibits high stablility in air at ambient temperature and strong photoluminescence at room temperature.

Structures and fluorescence properties of two novel metal-organic frameworks based on the bis(2-benzimidazole) and aromatic carboxylate ligands

Abstract Two new metal-organic frameworks, [Cd2(H2C3PIm)(BDC)4(H2O)3]n (1) and [Zn3(H2C3PIm)3 (BTC)2(H2O)2]n (2) (H2C3PIm = 2,2′-(1,3-propanediyl)bis(1 H-benzimidazole), H2BDC = 1,4-benzenedicarboxylic acid, H3BTC = 1,3,5-benzene tricarboxylic acid), have been synthesized hydrothermally and their structures are characterized by single crystal X-ray analysis. Compound 1 presents a 1D columnar structure, and compound 2 exhibits a 2D sheet with novel extra-large rings of 4.82 topology. Both complexes exhibit strong photoluminescence at room temperature.

Lanthanide Luminescent Coordination Polymer Constructed from Unsymmetrical Dinuclear Building Blocks Based on 4-((1H-Benzo[d]imidazol-1-yl)methyl)benzoic Acid

Lanthanide coordination polymers of the general formula [Ln2(L)5(NO3)(H2O)4]n (Ln = Eu (1), Tb (2), Gd (3)) supported by a novel aromatic carboxylate ligand 4-((1H-benzo[d]imidazol-1-yl)methyl)benz...

Synthesis and crystal structures of nickel(II) supramolecules containing hexaazamacrocycles and aromatic carboxylate ligands

Two new nickel(II) complexes, {[Ni(L)(4,4′-bpdc)] · 3H2O} n (1) and {[Ni(L)(2,6-ndc)] · 2CH3CN} n (2) (L = 1,8-dihydroxylethyl-1,3,6,8,10,13-hexaazacyclotetradecane, 4,4′-bpdc = 4,4′-biphenyldicarboxylate, 2,6-ndc = 2,6-naphthalenedicarboxylate), have been synthesized and structurally characterized by spectroscopic and X-ray diffraction methods. Compound 1 shows a 3-D supramolecule which is composed of two different series of 1-D coordination polymers, where each 1-D chain runs in different directions and interacts by π–π stacking at the intersection. Compound 2 contains 1-D coordination polymers in which 1-D chains run in the same direction. The 1-D chains are interconnected by hydrogen bonds in an undulated fashion to form a 3-D supramolecule.

Synthesis and Spectroscopic and Computational Characterization of Zn4O(Alicyclic or Aromatic Carboxylate)6 Complexes as Potential MOF Precursors

Potential metal-organic-framework precursors, Zn(4)O complexes with various alicyclic or aromatic carboxylate ligands, were prepared, in many cases quantitatively, from ZnO and the relevant carboxylic acids in the presence of trace amounts of water. The complexes obtained were characterized with various classical (titration) and instrumental (IR and NMR spectroscopies) methods and molecular modeling (PM3 and PM6 semiempirical quantum chemical methods and HF/6-31G** ab initio calculations). Structural peculiarities reflected in the success or failure in the synthesis could be rationalized with the combination of IR and NMR spectroscopies and molecular modeling.

Synthesis, Crystal Structure, and Photoluminescence of Homodinuclear Lanthanide 4-(Dibenzylamino)benzoate Complexes

Three new binuclear lanthanide complexes of general formula [Ln(2)(L)(6)(H(2)O)(4)] (Ln = Tb (1), Eu (2), and Gd (3)) supported by the novel aromatic carboxylate ligand 4-(dibenzylamino)benzoic acid (HL) have been synthesized. Complexes 1 and 2 were structurally characterized by single-crystal X-ray diffraction. Both 1 and 2 crystallize in the triclinic space group P(1), and their molecular structures consist of homodinuclear species that are bridged by two oxygen atoms from two carboxylate ligands via different coordination modes. The discrete bridged dimer of 1 is centrosymmetric and features 8-coordinate terbium atoms, each of which adopts a distorted square-antiprismatic geometry. Both coordination spheres comprise two eta(2)-chelating benzoates, two mu-eta(1):eta(1)-carboxylate interactions from the bridging benzoates, and two water molecules. By contrast, in complex 2, the Eu(3+) ion coordination environment is best described as a distorted tricapped-trigonal prism, each europium ion being coordinated to three eta(2)-chelating benzoate ligands and two water molecules. One of the eta(2)-carboxylate ligands is involved in a further interaction with an adjacent metal, thus rendering the overall binding mode bridging tridentate, mu-eta(2):eta(1). Scrutiny of the packing diagrams for 1 and 2 revealed the existence of a one-dimensional molecular array that is held together by intermolecular hydrogen-bonding interactions. The Tb(3+) complex 1 exhibits high green luminescence efficiency in the solid state with a quantum yield of 82%. On the other hand, poor luminescence efficiency has been noted for the Eu(3+)-4-(dibenzylamino)benzoate complex.

Structural Variation from 1D to 3D: Effects of Temperature and pH Value on the Construction of Co(II)-H2tbip/bpp Mixed Ligands System

To determine the influence of reaction conditions on the formation of metal−organic frameworks, a series of Co(II)/H2tbip/bpp complexes, {[Co2(tbip)2(H2O)6]·8H2O}n (1), {[Co(tbip)(bpp)(H2O)]2·4H2O}n (2), {[Co(tbip)(bpp)]·H2O}n (3), {[Co2(H2O)(tbip)(Htbip)2(bpp)2]·0.5(H2tbip)·0.5H2O}n (4), {[Co3(OH)(tbip)2(Htbip)(bpp)]}n (5) (H2tbip = 5-tert-butyl isophthalic acid, bpp = 1,3-bi(4-pyridyl)propane), have been synthesized through the hydrothermal reaction of cobalt(II) acetate, H2tbip, and bpp under different temperatures and pH conditions. The diverse product structures show the marked sensitivity of the structural chemistry of the aromatic carboxylate ligand to synthesis conditions. Polymer 1, which features a three-dimensional (3D) framework with CdSO4 topology, has carboxylate bridging polymeric chains spanning two different directions and bridging water molecules between these chains, and is formed at pH = 4 at 120 °C. At pH = 6, a one-dimensional tube-like structure of 2 is formed. Further increase of t...

Four Novel Three-Dimensional Pillared-Layer Metal-Organic Frameworks in the Zn/Triazolate/Carboxylate System: Hydrothermal Synthesis, Crystal Structure, and Luminescence Properties

Four novel zinc(II) metal-organic frameworks, {[Zn7(trz)6(1,3-bdc)4(H2O)2]·2H2O}n (1), {[Zn7(trz)6(hip)4(H2O)2]·8H2O}n (2), [Zn4(trz)4(Hnip)2(nip)]n (3), and [Zn5(trz)2(Hbtc)4(H2O)4]n (4) (Htrz = 1,2,4-triazole, 1,3-H2bdc = 1,3-benzenedicarboxylic acid, H2hip = 5-hydroxyisophthalic acid, H2nip = 5-nitroisophthalic acid, and H3btc = 1,3,5-benzenetricarboxylic acid), have been hydrothermally synthesized by reaction of Zn salt and Htrz with four different aromatic acids, respectively. Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by X-ray powder diffraction, elemental analyses, IR spectra, and TG analyses. The structures of compounds 1 and 2 are isostructural and feature the 3D structure containing multidimensional intersecting ring channels formed by the interconnection of 2D layers {[Zn7(trz)6]8+}n with 1,3-bdc (1) or hip (2). Compound 3 consists of {[Zn4(trz)4]4+}n layers with (4, 82) topology arranged in the −ABAB− stacking sequence, which are connected by nip pillars to generate a novel 3D open framework. Compound 4 is also in a 3D structure containing 2D layer motifs, which are further linked by btc ligands to complete the structure. There are two different building units [Zn2(trz)2]2+ and [ZnO6] within the 2D layers of 4. All of the compounds 1−4 exhibit the 3D pillared-layer structures. In the 2D layer motifs of these four compounds, trz ligands connect Zn ions in different coordination modes, which reflect the tendency of the trz ligand to bridge multiple metal sites, and the aromatic carboxylate ligands in compounds 1−4 serve as the pillar between the 2D layers, creating the 3D open frameworks. Moreover, these four compounds exhibit emission properties at room temperature in the solid state.

Oxidation of anethole with hydrogen peroxide catalyzed by oxovanadium aromatic carboxylate complexes

Abstract Selective oxidation of anethole with hydrogen peroxide to anisaldehyde has been developed using a novel efficient catalytic process by oxovanadium complexes bearing aromatic carboxylate ligands such as phthalate, salicylate and benzoate. Under mild reaction conditions (4 h at 303 K), oxovanadium(IV) phthalate complex (OPC) (IV) provided the best results with 100% conversion of anethole and 73.5% selectivity for anisaldehyde at low catalyst loading (∼0.5 mol%). Inspiringly, H 2 O 2 can be stoichiometrically used (H 2 O 2 :anethole = 2:1) for the complete conversion.

PH-Dependent Assembly of Supramolecular Architectures from 0D to 2D Networks

Five Cu(II)/benzoate/4,4‘-bipy complexes, namely, [Cu(H2O)(benzoate)2(4,4‘-bipy)2](benzoic acid)2·(4,4‘-bipy) (1), [Cu2(H2O)2(benzoate)4(4,4‘-bipy)3]·(H2O)9 (2), [Cu2(benzoate)4(4,4‘-bipy)3] (3), [Cu3(H2O)4(benzoate)6(4,4‘-bipy)4.5]·(4,4‘-bipy)·(H2O)5 (4), and [Cu3(OH)2(H2O)2(benzoate)4(4,4‘-bipy)2] (5) (4,4‘-bipy = 4,4‘-bipyridine), have been synthesized through hydrothermal reaction of copper(II) nitrate, benzoic acid, and 4,4‘-bipyridine under different pH conditions. The diverse product structures show the marked sensitivity of the structural chemistry of the aromatic carboxylate ligand to synthesis conditions. Complex 1, which exhibits a zero-dimensional (0D) structure of mononuclear copper(II), is formed at pH = 5.5. At pH = 6.0, dimeric copper(II) complexes of 2 and 3 are formed. Reaction at pH = 7 leads to a one-dimensional (1D) structure of 4. A further increase of the pH to 8.0 results in a two-dimensional (2D) structure of 5. Crystal data are monoclinic, space group P2/n, a = 13.992(4) A, b = 5...

Spectroscopic investigations of complexes between Eu(III) and aromatic carboxylic ligands

In order to obtain information on the number and symmetry of the different Eu3+ complexes formed with several hydroxybenzoic acids, ultra-low temperature luminescence measurements at 4.7 K were carried out. Hydroxybenzoic acids were used as simple model compounds for metal binding structures in humic substances (HS). Information on the complexes was extracted from high-resolution total luminescence spectra (TLS), which were obtained by scanning through the 5D0 ← 7F0 transition of Eu(III) with a pulsed dye laser and measuring the emission in the wavelength range of the 5D0 → 7F1 and 5D0 → 7F2 transitions simultaneously. By extracting the crystal field strength parameter Nv(B2q) from the TLS, it was found that Nv(B2q) was not directly correlated with the excitation energy. Further, the symmetry of the individual complexes formed was extracted from the experimental data.

Microporous Metal–Organic Framework Constructed from Heptanuclear Zinc Carboxylate Secondary Building Units

A novel, three-dimensional, noninterpenetrating microporous metal-organic framework (MOF), [Zn7O2(pda)5(H2O)2]5 DMF4 EtOH 6 H2O (1) (H2PDA=p-phenylenediacrylic acid, DMF=N,N-dimethylformamide, EtOH=ethanol), was synthesized by constructing heptanuclear zinc carboxylate secondary building units (SBUs) and by using rigid and linear aromatic carboxylate ligands, PDA. The X-ray crystallographic data reveals that the seven zinc centers of 1 are held together with ten carboxylate groups of the PDA ligands and four water molecules to form a heptametallic SBU, Zn7O4(CO2)10, with dimensions of 9.8 x 9.8 x 13.8 A3. Furthermore, the heptametallic SBUs are interconnected by PDA acting as linkers, thereby generating an extended network with a three-dimensional, noninterpenetrating, intersecting large-channel system with spacing of about 17.3 A. As a microporous framework, polymer 1 shows adsorption behavior that is favorable towards H2O and CH3OH, and substantial H2 uptake. In terms of the heptanuclear zinc carboxylate SBUs, polymer 1 exhibits interesting photoelectronic properties, which would facilitate the exploration of new types of semiconducting materials, especially among MOFs containing multinuclear metal carboxylate SBUs.

Synthesis and Characterization of Platinum(IV) Anticancer Drugs with Functionalized Aromatic Carboxylate Ligands: Influence of the Ligands on Drug Efficacies and Uptake

A series of trans-platinum(IV) complexes with functionalized aromatic carboxylate ligands, cis,cis,trans-Pt(NH3)2Cl2(CO2C6H4R)2 (R = H (3), p-vinyl (4), p-methoxy (5), p-iodo (6), p-cyano (7), or o-carboxyl (8)) was synthesized and characterized by spectroscopic methods. Crystal structures of 3, 4, 7, and 8 were obtained, which revealed that their structural conformations were influenced by intramolecular H-bonding interactions. The complexes were evaluated for cellular uptake and inhibition of cell proliferation against a panel of lung, colon, and breast carcinoma cell lines. The functionalization of the aromatic carboxylate ligand was found to have a profound influence on the uptake, and hence, efficacy, of this class of complex.

Effect of ligand structure on synergism in Tb 3+-aromatic acid complexes: fluorescence lifetime studies

The fluorescence of Tb 3+ sensitized by aromatic carboxylic acid ligands (benzoic, monomethylphthalic, monomethylterephthalic, trimesic, terephthalic, isophthalic, phthalic and mellitic acids) and the synergism displayed by these complexes when treated with TOPO/Triton X-100 have been studied by measuring lifetimes of Tb 3+ emission. The lifetime of Tb 3+ fluorescence was not significantly altered following complex formation with aromatic carboxylic acids, even though a significant enhancement in the Tb 3+ fluorescence intensity was observed in every single case. However, when these Tb 3+-aromatic acid complexes were treated with TOPO/Triton X-100, the lifetimes of the Tb 3+ fluorescence increased markedly, but only with certain acids. Interestingly, even amongst the acids that showed an increase in lifetime with TOPO/Triton X-100, the lifetimes as a function of the pH of the solution was strongly dependent on the structure of the ligand. These differences and the reasons for such behavior are discussed, which shed light on the role of the structure of the ligand on the synergism process.