Carboxylate-containing Ligands Research Articles

Technetium Complexation with Multidentate Carboxylate-Containing Ligands: Trends in Redox and Solubility Phenomena.

The chemistry of technetium (t1/2(99Tc) = 2.11 × 105 years) is of particular importance in the context of nuclear waste disposal and historic contaminated sites. Polycarboxylate ligands may be present in some sites and are potentially capable of strong complexing interactions, thus increasing the solubility and mobility of 99Tc under environmentally relevant conditions. This work aimed to determine the impact of five organic complexing ligands [L = oxalate, phthalate, citrate, nitrilotriacetate (NTA), and ethylenediaminetetraacetate (EDTA)] under anoxic, alkaline conditions (pH ≈ 9-13) on the solubility of technetium. X-ray absorption spectroscopy confirmed that TcO2(am,hyd) remained the solubility-controlling solid phase in undersaturation solubility experiments. Ligands with maximum coordination numbers (CN) ≥ 3 (EDTA, NTA, and citrate) exhibited an increase in solubility from pH 9 to 11, while ligands with CN ≤ 2 (oxalate and phthalate) at all investigated pH and CN ≥ 3 at pH ≈ 13 were outcompeted by hydrolysis reactions. Though most available thermodynamic values were determined under acidic conditions, these models satisfactorily explained high-pH undersaturation solubility of technetium for citrate and NTA, whereas experimental data for Tc(IV)-EDTA were highly overestimated. This work illustrates the predominance of hydrolysis under hyperalkaline conditions and provides experimental support for existing thermodynamic models of Tc-L except Tc-EDTA, which requires further research regarding aqueous speciation and solubility.

A Zn(II) complex with a pyridyl- and carboxylate-containing ligand: synthesis and structural characterization

Abstract The hydrothermal reaction of Zn(II) nitrate hydrate with 5-(pyridin-4-yl)isophthalic acid (H2L) yields the complex [Zn2(L)2(H2O)2] · 2(H2O) (1), which has been characterized by single crystal X-ray diffraction, IR spectroscopic, elemental, and thermogravimetric analyses. Complex 1 exhibits a 3-nodal (3,6)-connected 2D net structure with (4.62)2(42.610.83)(63)4 topology. Its luminescence property was investigated, but the results show that the coordination to the zinc atom has no significant effect on the emission of the ligand.

Synthesis, crystal structure and desulfurization properties of zig-zag 1D coordination polymer of copper(II) containing 4-methoxybenzoic acid ligand

ABSTRACTCombustion of fuels containing organosulfur compounds has resulted in the emission of sulfur oxides (SOx) into the atmosphere, therefore, causing serious environmental and health hazards. Herein, slightly distorted octahedral zig-zag 1D coordination polymer of copper(II) [Cu(4-mba)2(H2O)3] was synthesized by reacting copper sulfate pentahydrate with a carboxylate-containing ligand (H-4mba = 4-methoxybenzoic acid) and employed for sulfur compound uptake. The ligand coordinates to the copper(II) atom via two pairs of deprotonated ligating atoms (carboxylate oxygens) and two water molecules. Structural characterization also reveals that interplay of O–H···O, N–H···O, C-H···O and C–H···π interactions between lattice and coordinated water and ligands significantly contribute to the crystal packing leading to the formation and strengthening of three-dimensional supramolecular assembly. The complex, [Cu(4-mba)2(H2O)3], show potential for desulfurization of fuel with an observed adsorption capacity of 9.6 mg/g at 32°C for 6 h. DFT calculations further revealed a transfer of electron sulfur-containing compounds and the complex, [Cu(4-mba)2(H2O)3], thus leading to a stronger pi–pi interaction.

The structure and binding mode of citrate in the stabilization of gold nanoparticles.

Elucidating the binding mode of carboxylate-containing ligands to gold nanoparticles (AuNPs) is crucial to understand their stabilizing role. A detailed picture of the three-dimensional structure and coordination modes of citrate, acetate, succinate and glutarate to AuNPs is obtained by 13C and 23Na solid-state NMR in combination with computational modelling and electron microscopy. The binding between the carboxylates and the AuNP surface is found to occur in three different modes. These three modes are simultaneously present at low citrate to gold ratios, while a monocarboxylate monodentate (1κO1) mode is favoured at high citrate:gold ratios. The surface AuNP atoms are found to be predominantly in the zero oxidation state after citrate coordination, although trace amounts of Auδ+ are observed. 23Na NMR experiments show that Na+ ions are present near the gold surface, indicating that carboxylate binding occurs as a 2e- L-type interaction for each oxygen atom involved. This approach has broad potential to probe the binding of a variety of ligands to metal nanoparticles.

Uranyl-Peroxide Clusters Incorporating Iron Trimers and Bridging by Bisphosphonate- and Carboxylate-Containing Ligands.

A hybrid uranium-iron cage nanocluster, [(UO2)24(FeOH)24(O2)24(PO4)8(CH(COO)(PO3)2)24]96- (U24Fe24), was synthesized using bridging ligands containing bisphosphonate and carboxylate groups. U24Fe24 contains six tetramers of uranyl hexagonal bipyramids and eight iron trimers, each of which consists of three corner-sharing Fe3+ octahedra and is stabilized by in situ formed phosphate and 2,2-bis(phosphonato)acetate (C2P2) groups. Tetramers and trimers are bridged by 24 C2P2 groups into a cage cluster. Crystals of U24Fe24 present a paramagnetic-like behavior. X-ray scattering showed that U24Fe24 forms in the reactant solution prior to crystallization and is stable upon dissolution in water.

ChemInform Abstract: An Introduction to Synthesis and Application of Nanoscale Metal‐Carboxylate Coordination Polymers

AbstractReview: 107 refs.

An introduction to synthesis and application of nanoscale metal–carboxylate coordination polymers

In recent years, nanoscale metal–organic coordination polymers have attracted more and more attention because of their specific properties in gas sorption, sensors, contrast agents, drug delivery, templates and so on. Carboxylate compounds are a large family of O-donor ligands and are studied widely because such ligands can be designed with various structures and can also form strong bonds with metal centers. Until now, many nanoscale metal–organic coordination polymers with carboxylate-containing ligands have been reported. The purpose of this tutorial highlight is to present recent advances in the syntheses of nanoscale metal–carboxylate coordination polymers and illustrate the potential application of this new class of nanomaterials in different areas.

Zn(phen)(O,N,O)(H2O)] and [Zn(phen)(O,N)(H2O)] with O,N,O is 2,6-dipicolinate and N,O is l-threoninate: synthesis, characterization, and biomedical properties

Two ternary Zn(II) complexes, with 1,10-phenanthroline (phen) as the main ligand and a carboxylate-containing ligand [dipicolinate (dipico) or L-threoninate (L-Thr)] as the subsidiary ligand, were prepared and characterized by elemental analysis, Fourier transform IR, UV, and fluorescence spectroscopy, X-ray diffraction, molar conductivity, and electrospray ionization mass spectrometry. X-ray structure analysis shows that both [Zn(phen)(dipico)(H(2)O)]·H(2)O (1) and [Zn(phen)(L-Thr)(H(2)O)Cl]·2H(2)O (2) have octahedral geometry about the Zn(II) atom. Both complexes can inhibit topoisomerase I, and have better anticancer activity than cisplatin against nasopharyngeal cancer cell lines, HK1 and HONE-1, with concentrations causing 50% inhibition of cell proliferation (IC(50)) in the low micromolar range. Complex 2 has the highest therapeutic index for HK1. Both Zn(II) complexes can induce cell death by apoptosis. Changing the subsidiary ligand in the Zn(II) complexes affects the UV-fluorescence spectral properties of the coordinated phen ligand, the binding affinity for some DNA sequences, nucleobase sequence-selective binding, the phase at which cell cycle progression was arrested for treated cancer cells, and their therapeutic index.

Synthesis, structure and property of lanthanide–organic frameworks with pyridyl- and carboxylate-containing ligand

Three new lanthanide–organic frameworks {[La(IP-py)(HIP-py)(H2O)2]·H2O}n (1), {[Sm2(IP-py)2(IP-pyH)2(H2O)2]·12H2O}n (2) and {[Tb3(IP-py)4(IP-pyH)(H2O)5]·9H2O}n (3) have been prepared by reactions of the corresponding lanthanide salt with 5-(isonicotinamido)isophthalic acid (H2IP-py). The complexes have been fully characterized by means of IR, elemental analyses and single-crystal X-ray diffraction. In compounds 1–3, the lanthanide centers are eight- and nine-coordinated with different coordination geometries and the carboxylate groups of the ligand show different coordination modes leading to the formation of different 2D network structures which are well-defined by the bulky and inert functional groups. Interestingly an unprecedented 2D network of water molecules was observed in complex 2. The luminescent properties of complexes 2 and 3 were investigated.

Metal–organic frameworks with pyridyl- and carboxylate-containing ligands: syntheses, structures and properties

Assembly reactions of pyridyl- and carboxylate-containing ligand 5-(isonicotinamido)isophthalic acid (H2INAIP) with corresponding metal salts result in formation of six new coordination polymers, namely {[Mn(INAIP)(DMF)]·0.5DMF}n (1), {[Mn(INAIP)(H2O)2]·4H2O}n (2), {[Co(INAIP)(H2O)]·2H2O}n (3), {[Co(INAIP)(bpy)0.5]}n (4), {[Co(INAIP)(Him)(H2O)]·H2O}n (5), and {[Cu(INAIP)(Him)(H2O)]·H2O}n (6) (DMF = N,N-dimethylformamide, bpy = 4,4′-bipyridine, Him = imidazole). The results of single-crystal X-ray diffraction analysis indicate that 1 is a two-fold interpenetrated three-dimensional (3D) framework with sra topology, complexes 2, 5 and 6 have two-dimensional (2D) network structure with (6,3) topology, while 3 and 4 have infinite 2D bi-layer structure with different topologies. Complex 3 exhibits a 4-connected network with the Schlafli symbol (43·63), and 4 displays a (4,5)-connected net with Schlafli symbol (43·52·6)(43·55·62). The magnetic and adsorption properties of the complexes were investigated.

Azide Groups in Higher Oxidation State Manganese Cluster Chemistry: From Structural Aesthetics to Single-Molecule Magnets

This Forum Article overviews the recent amalgamation of two long-established areas, manganese/oxo coordination cluster chemistry involving the higher Mn(II)/Mn(IV) oxidation states and transition-metal azide (N(3)(-)) chemistry. The combination of azide and alkoxide- or carboxylate-containing ligands in Mn chemistry has led to a variety of new polynuclear clusters, high-spin molecules, and single-molecule magnets, with metal nuclearities ranging from Mn(4) to Mn(32) and with ground-state spin values as large as S = 83/2. The organic bridging/chelating ligands are discussed separately as follows: (i) pyridyl alkoxides [the anions of 2-(hydroxymethyl)pyridine (hmpH), 2,6-pyridinedimethanol (pdmH(2)), and the gem-diol form of di-2-pyridyl ketone (dpkdH(2))]; (ii) non-pyridyl alkoxides [the anions of 1,1,1-tris(hydroxymethyl)ethane (thmeH(3)), triethanolamine (teaH(3)), and N-methyldiethanolamine (mdaH(2))]; (iii) other alcohols [the anions of 2,6-dihydroxymethyl-4-methylphenol (LH(3)) and Schiff bases]; (iv) pyridyl monoximes/dioximes [the anions of methyl-2-pyridyl ketone oxime (mpkoH), phenyl-2-pyridyl ketone oxime (ppkoH), and 2,6-diacetylpyridine dioxime (dapdoH(2))]; (v) non-pyridyl oximes [the anions of salicylaldoxime (saoH(2)) and its derivatives R-saoH(2)]. The large structural diversity of the resulting complexes stems from the combined ability of the azide and organic ligands to adopt a variety of ligation and bridging modes. The combined work demonstrates the synthetic novelty that arises when azide is used in conjunction with alcohol-based chelates, the aesthetic beauty of the resulting molecules, and the often fascinating magnetic properties that these compounds possess. This continues to emphasize the extensive and remarkable ability of Mn chemistry to satisfy a variety of different tastes.

Crystal structure of triaqua-cis-bis((2-carboxybenzene)sulfonylglycinato) zinc(II), Zn(H2O)3(C9H8NO6S)2

C18H22N2O15S2Zn, orthorhombic, Pnna (no. 52), a = 11.0915(9) A, b = 42.064(4) A, c = 5.0972(4) A, V = 2378.1 A, Z = 4, Rgt(F) = 0.030, wRref(F) = 0.088, T = 292 K. Source of material The mixture of ZnCl2 · 2H2O (1 mmol) and 3-(sulfonyl-glycine)benzoic acid (2 mmol) was stirred into 15mL aqueous solution at room temperature. Then the pH was adjusted to approximately 7 with 1 M KOH solution. And then 5 mL ethanol solution of 4,4 bipyridine (1 mmol) was added. The reaction mixture was then heated on awater bath for 6 h at 70 °C, and then filtered. Colorless crystal were obtained from themother liquor by slow evaporation at room temperature after 6 weeks. Experimental details All hydrogen atoms were first found in the difference electron densitymaps, and then placed in the calculated positions. The hydrogen atoms of carboxylate group and water molecules were found from Fourier difference maps and refined freely. The remaining H atoms were refined by riding model with Ueq(H) = 1.2Ueq(C). Discussion Crystal engineering ofmetal-organic frameworks (MOFs) is realizable by the choice of metals and the numerous choice and design of ligands, which bears the weight of prospective applications in new chemical separation, ion exchange, and gas adsorption [1-6]. In particular, carboxylate ligands have been frequently employed in the construction of microporous inorganic/organic hybrid materials for gas storage purposes. In this context, benzenedicarboxylic acid and their derivatives (such as 1,3-benzenedicarboxylic acid, 1,4-benzenedicarboxylic acid or 5-hydroxyisophtalic acid) are widely used as building blocks to link metal ions to produce interesting metal-organic framework structures and properties [7-10]. However, much fewer studies on coordination chemistry of flexible carboxylate-containing ligands have been carried out. On the other hand, the main strategies used in the field of crystal engineering are basically on the use of either conventional coordinative bonds or weak interactions. Among the non-covalent interactions, hydrogen bonding interactions play important role in designing superstructures and have attracted much interest due to their relative strength and directionality [11-12]. 3-(Sulfonyl-glycine)benzoic acid can act not only as hydrogen bond acceptors but also as hydrogen bond donors,whichmake it a wonderful candidate for the construction of supramolecular networks. The crystal structure consists of the mononuclear molecules. The coordinating 3-(sulfonyl-glycine)benzoic acid exists as a monoanion acting as a monodentate ligand. In the complex, zinc atom is five-coordinated in a distorted trigonal-bipyramidal ZnO5 environment, in which the basal coordination sites are occupied by three oxygen atoms (O1, O1A, O7), with the bond lengths of 1.968(1) A, 1.968(1) A and 2.071(3) A, respectively. The axial position is occupied by two oxygen atoms (O8, O8A) fromwater molecules, with the bond lengths of both 2.076(2) A. There exist intermolecular hydrogen bonds between carboxylate oxygen atoms fromC6H5COOgroup (O···O distances of 2.635A), forming 1D hydrogen bonded chains in which six-membered-ring and mononuclear units are alternately arranged along [100]. These chains are assembled by hydrogen bonds between carboxylate oxygen atoms from amino acid and water molecules from adjacent chains to give rise to 2D layer supramolecular structure (O···O distances of 2.835 A). At the same time, several weaker O–H···O hydrogen bonds are formed: (a) hydrogen bonding between water oxygen atoms and oxygen atoms of sulfonamide groups (O8–H2W···O5) with the bond distance of 3.211(2) A and bond angle of 117(3)°, (b) hydrogen bonding betweenwater oxygen atoms and oxygen atoms of amino acid groups (O7–H3W···O1 and O7–H3W···O2), with the bond distances of 3.117(3) A and 3.035(2)Aandbond angles of 118(3)° and 147(4)°, respectively. Z. Kristallogr. NCS 222 (2007) 435-436 / DOI 10.1524/ncrs.2007.0184 435 © by Oldenbourg Wissenschaftsverlag, Munchen

Synthesis and Crystal Structure of One-Dimensional Carboxylate-Bridged Copper(II) Complex with 2-Pyridylmethylamino-3-butyric acid

The tridentate Schiff base carboxylate-containing ligand 2-pyridylmethylamino-3-butyric acid (Hpaba) reacts with copper(II) perchlorate to give the one-dimensional chain complex {[Cu(μ-paba)](ClO4)·H2O} n (1). The coordination geometry of each copper(II) ion is best described as a square-plane with two nitrogen atoms and one carboxylate oxygen atom of the ligand, and one carboxylate oxygen atom belong to another ligand. It crystallizes in the monoclinic system P21/c with a = 12.717(2), b = 7.9163(15), c = 14.981(2) A, β = 111.14(1)°, V = 1406.8(4) A3, Z = 4. Cyclic voltammogram of 1 undergoes the reversible one-electron oxidation to the Cu(III) and the reversible one-electron reduction to the Cu(I) state. Crystal structure of 1 reveals a syn-anti carboxylate-bridged one dimensional chain complex in which the coordination environment around each copper(II) ion exhibits a distorted square plane.

Regiospecific Ligand Oxygenation in Iron Complexes of a Carboxylate‐Containing Ligand Mediated by a Proposed FeV–Oxo Species

Regiospecific Ligand Oxygenation in Iron Complexes of a Carboxylate‐Containing Ligand Mediated by a Proposed Fe^V–Oxo Species

Syntheses, Crystal Structures, and Magnetic Properties of Carboxylate-Bridged Copper(II) Complexes with Bis(2-Pyridylmethyl)Amino Acids

Tetradentate Schiff-base carboxylate-containing ligands, bis(2-pyridylmethyl)amino-5-valeric acid (Hpmva) and bis(2-pyridylmethyl)amino-6-caproic acid (Hpmca), react with copper(II) perchlorate to give rise to the carboxylated bridged chain complexes {[Cu(μ-pmva)(H2O)](ClO4)}n (1) and {[Cu(μ-pmca)(H2O)](ClO4)}n (2). These complexes have been characterized by X-ray crystallography, spectroscopic, and variable-temperature magnetic susceptibility measurements. In 1 and 2, each of the copper(II) ions exhibit CuN3O2 coordination environments with the three nitrogen atoms of the ligand and one oxygen atom belonging to the carboxylate group of an adjacent molecule occupying the basal position and a water molecule coordinated in the axial position. The electronic spectra of the complexes are significantly affected by the coordination geometry. Magnetic susceptibility measurements indicate that complexes exhibit very weak ferromagnetic interactions.

Carboxylate-bridged helical-chain Cu(II) complex and zig-zag chain Ni(II) and Co(II) complexes from 8-quinolinyloxyacetate

Tridentate carboxylate-containing ligand L (L=8-quinolinyloxyacetate) reacts with M(II) chloride (M=Cu, Ni and Co) to give rise to three coordination polymers [CuLCl] n ( 1), {[NiL(H 2O) 2]Cl·H 2O} n ( 2), and {[CoL(H 2O) 2]Cl·H 2O} n ( 3), respectively. Complex 1 is a helix chain polymer while 2 and 3 are two zig-zag chain polymers. The bridging carboxylate groups are in anti– anti bridging mode in complex 1 while they are within syn– anti conformation in 2 and 3. In 1, carboxylate groups link two basal positions in basal–apical, while in complexes 2 and 3, they are basal–basal positions. The structures of these complexes have been determined by X-ray crystallography. Interestingly, three chain complexes are also linked to form 3D networks through hydrogen bonds.

Crystal structure of monomeric sarcosine oxidase from Bacillus sp. NS-129 reveals multiple conformations at the active-site loop

Monomeric sarcosine oxidase (MSOX) is a flavoprotein that catalyzes the oxidation of sarcosine to generate formaldehyde, glycine, and hydrogen peroxide, and is utilized in quantification of creatinine in serum. Crystal structure of MSOX from Bacillus sp. NS-129 (without ligand) has been determined at 1.86 A Unlike the published structures of MSOX from Bacillus sp. B-0618 (without or with carboxylate-containing ligand), the two molecules in the asymmetric unit adopt distinct conformations at the active site loop (Gly56 to Glu60) with a maximal root-mean-square (RMS) displacement of 3.3 A for Cα atom of Arg59. The multiple conformations seen at the active-site loop suggest that high flexibility of the loop would be important for the activity of MSOX. (Communicated by Masanori OTSUKA, M.J.A.)

The trimethylammonium headgroup of choline is a major determinant for substrate binding and specificity in choline oxidase

Choline oxidase catalyzes the oxidation of choline to glycine betaine via two sequential flavin-linked transfers of hydride equivalents to molecular oxygen and formation of a betaine aldehyde intermediate. In the present study, choline and glycine betaine analogs were used as substrates and inhibitors for the enzyme to investigate the structural determinants that are relevant for substrate recognition and specificity. Competitive inhibition patterns with respect to choline were determined for a number of substituted amines at pH 6.5 and 25 °C. The K is values for the carboxylate-containing ligands glycine betaine, N, N-dimethylglycine, and N-methylglycine increased monotonically with decreasing number of methyl groups, consistent with the trimethylammonium portion of the ligand being important for binding. In contrast, the acetate portion of glycine betaine did not contribute to binding, as suggested by lack of changes in the K is values upon substituting glycine betaine with inhibitors containing methyl, ethyl, allyl, and 2-amino-ethyl side chains. In agreement with the inhibition data, the specificity of the enzyme for the organic substrate ( k cat/ K m value) decreased when N, N-dimethylethanolamine, N-methylethanolamine, and the isosteric substrate 3,3-dimethyl-1-butanol were used as substrate instead of choline; a contribution of ∼7 kcal mol −1 toward substrate discrimination was estimated for the interaction of the trimethylammonium portion of the substrate with the active site of choline oxidase.

Synthesis, Properties and Crystal Structures of Mononuclear Copper(II) Complexes with Bis(2-Pyridylmethyl)Amino Acids

Tetradentate Schiff-base carboxylate-containing ligands, bis(2-pyridylmethyl)amino-3-propionic acid (Hpmpa) and bis(2-pyridylmethyl)amino-4-butyric acid (Hpmba), react with CuCl2 to give rise to the mononuclear complexes [Cu(Hpmpa)Cl]Cl · 2H2O (1) and [Cu(Hpmba)Cl2]· H2O (2). These complexes have been characterized by X-ray crystallography, spectroscopic and cyclic voltammetry. Crystal structure of (1) shows that the copper(II) ion has a distorted square-pyramidal geometry with the three nitrogen atoms of the Hpmpa ligand and one chloride anion occupying the basal plane and an oxygen atom from the carboxylate group coordinating the axial position. In (2), the coordination environment around the copper(II) ion reveals a distorted square-pyramids with three nitrogen atoms of the Hpmba ligand and one chloride anion that comprise the basal plane, whereas the apical position is filled by the chloride anion. Cyclic voltammetry of the complexes gives two one-electron waves corresponding to CuII/CuIII and CuIII/CuI processes. The electronic spectra and redox potentials of the complexes are influenced significantly by the N-pendant carboxylate groups.

Synthesis and characterization of syn– anti carboxylate-bridged one-dimensional copper(II) complexes with bis(2-pyridylmethyl)amino acids

Tetradentate Schiff-base carboxylate-containing ligands, bis(2-pyridylmethyl)amino-2-ethanoic acid (pmea), bis(2-pyridylmethyl)amino-3-propionic acid (pmpa) and bis(2-pyridylmethyl)amino-4-butyric acid (pmba), react with copper(II) perchlorate to give rise to the one-dimensional polymeric chain complexes {[Cu(μ-pmea)](ClO 4) · H 2O} n ( 1), {[Cu(μ-pmpa)](ClO 4) · 2H 2O} n ( 2) and {[Cu(μ-pmba)(H 2O)](ClO 4) · 3H 2O} n ( 3). These complexes have been characterized by X-ray crystallography, UV–Vis spectra and variable-temperature magnetic susceptibility measurements. In complexes 1– 3, distorted square-pyramidal copper(II) ions are sequentially bridged by syn– anti carboxylate groups. Each of the copper(II) ions exhibit CuN 3O 2 coordination environments with the three nitrogen atoms of the ligand and one oxygen atom belonging to the carboxylate group of an adjacent molecule occupying the basal positions and an oxygen atom (from a carboxylate group in the case of compounds 1–2 and from a water molecule in 3) coordinated in the axial position. The electronic spectra of the complexes are significantly affected by the coordination geometry. Magnetic susceptibility measurements indicate that complexes 1– 3 exhibit very weak ferromagnetic interactions. The magnetic behavior can be explained on the basis of the structural data.