Monodentate Carboxylate Groups Research Articles

Diaquabis(4-formylbenzoato-κO)zinc(II)

The ZnII atom in the title compound, [Zn(C8H5O3)2(H2O)2], which lies on a twofold rotation axis, is coordinated by two monodentate carboxyl­ate groups and two water mol­ecules in a tetra­hedral geometry; the geometry is distorted towards octa­hedral owing to two long Zn⋯Ocarbon­yl contacts [2.512 (2) Å]. Hydrogen-bonding inter­actions give rise to a three-dimensional network. The formyl group is disordered approximately equally over two positions.

Hydrothermal synthesis of uranyl–organic frameworks with pyrazine-2,3-dicarboxylate linkers

The reaction of uranyl nitrate with pyrazine-2,3-dicarboxylic acid (H2PZDC) under hydrothermal conditions and in the presence of different bases gave three novel polymeric assemblages. The complexes [UO2(PZDC)(H2O)2] (1) and [UO2(PZDC)(H2O)] (2), obtained with NMe4OH and pyridine as base, respectively, differ by the coordination mode of the ligand, with O,N-chelation and one monodentate carboxylate group in 1 and both O,N- and O,O-chelation (the latter involving both carboxylate groups) in 2. In both cases, one-dimensional coordination polymers are formed, which are further assembled into three-dimensional networks by hydrogen bonding. In the presence of CsOH as a base, the heterometallic complex [(UO2)2Cs(PZDC)2(OH)(H2O)] (3) was isolated, which is a compact, three-dimensional framework. One uranyl ion is bis-O,N-chelated and the other is bound to three monodentate ligands, whereas each cesium cation is bound to three uranyl oxo groups, one nitrogen and five carboxylate oxygen atoms. The metal atoms are further bridged by μ2-hydroxide and μ2-aqua ligands. One of the PZDC2− ligands in 3 assembles five metal atoms and the other four, thus demonstrating the potential of this molecule for the building of three-dimensional uranyl–organic frameworks.

Poly[diaquabis(2,2′-bipyridine)tris(μ4-2,2′-bipyridine-4,4′-dicarboxylato)dineodymium(III)

In the crystal structure of the title mixed-ligand coordination polymer, [Nd2(C12H6N2O4)3(C10H8N2)2(H2O)2]n, the NdIII ion is in an octa­hedral coordination environment formed by one water mol­ecule, one chelating 2,2′-bipyridine ligand, and five monodentate carboxyl­ate groups. The local coordination polyhedron around the NdIII ion is a bicapped trigonal prism. Two NdIII centers are bridged by four carboxyl­ate groups to form an Nd2 dimeric unit; these are further connected by 2,2′-bipyridine-4,4′-dicarboxyl­ate linkers, resulting in a layered coordination network.

Triorganoantimony(V) carboxylates: Synthesis, characterization and crystal structure of [Me 3Sb(O 2C–C 5H 4N) 2] · H 2O

Reactions of [R 3Sb(OPr i ) 2] with N-heterocylic carboxylic acids gave compounds of the type [R 3Sb(O 2C–Ar) 2] ( 1) (R = Me, Et, Pr i , Ph; Ar = 2-C 5H 4N, 2-C 9H 6N). The mono-bromo compound [Me 3Sb(Br)(O 2C–C 5H 4N)] ( 2) exists in equilibrium with [Me 3Sb(O 2C–C 5H 4N) 2] and [Me 3SbBr 2]. All new compounds have been characterized by IR and NMR ( 1H and 13C{ 1H}) spectral data. X-ray structural analysis of one example, [Me 3Sb(O 2C–C 5H 4N) 2], isolated as its monohydrate, revealed an essentially trigonal bipyramidal geometry for the antimony atom defined by three equilaterally disposed methyl groups and two oxygen atoms from monodentate carboxylate groups, in apical positions. The crystal structure is consolidated into a three-dimensional network by cooperative O–H⋯O, O–H⋯N and C–H⋯O interactions.

Mixed ligand complexes of Cu(II)-2-(2-pyridyl)-benzimidazole and aliphatic or aromatic dicarboxylic acids: Synthesis, characterization and biological activity

The synthesis and structural characterization of mixed ligand complexes derived from 2-(2-pyridyl)-benzimidazole (PBI) (1ry ligand) and aliphatic or aromatic dicarboxylic acids (2ry ligand) are reported. Cu(II) complexes were characterized on the bases of their elemental analyses, IR, ESR and thermal analyses. The elemental analysis indicated the formation of mixed ligand complexes in a mole ratio 1:1:1 (Cu:L 1:L 2), L 1 = PBI and L 2 = oxalic acid, phthalic acid or malonic acid. IR spectra showed that PBI acts as a neutral bidentate coordinated to the Cu(II) via the pyridyl and imidazolyl nitrogen atoms. The dicarboxylic acids are bidentate with monodentate carboxylate groups. Thermal decomposition study of complexes was monitored by thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis in N 2 atmosphere. The decomposition course and steps were analysed and the activation parameters of the nonisothermal decomposition were calculated from the TG curves and discussed. The isolated metal chelates were screened for their antimicrobial activities and the results are reported, discussed and compared with some known antibiotics.

Dinuclear Complexes Formed with the Triazacyclononane Derivative ENOTA4-: High-Pressure 17O NMR Evidence of an Associative Water Exchange on [MnII2(ENOTA)(H2O)2

Mn2+ has five unpaired d-electrons, a long electronic relaxation time, and labile water exchange, all of which make it an attractive candidate for contrast agent application in medical magnetic resonance imaging. In the quest for stable and nonlabile Mn2+ complexes, we explored a novel dimeric triazacyclononane-based ligand bearing carboxylate functional groups, H4ENOTA. The protonation constants of the ligand and the stability constants of the complexes formed with some endogenously important metals (Ca2+, Cu2+, Zn2+), as well as with Mn2+ and Ce3+, have been assessed by NMR methods, potentiometry, and UV-vis spectrophotometry. Overall, the thermodynamic stability of the complexes is lower as compared to that of the corresponding NOTA analogues (H3NOTA, 1,4,7-triaazacyclononane-1,4,7-triacetic acid). The crystal structure of Mn2(ENOTA)(H2O) x 5H2O contains two six-coordinated Mn2+, in addition to the three amine nitrogens and the two oxygens from the pendent monodentate carboxylate groups, and one water (Mn2) or one bridging carboxylate oxygen (Mn1) completes the coordination sphere of the metal ion. In an aqueous solution, this bridging carboxylate is replaced by a water molecule, as evidenced by the 17O chemical shifts and proton relaxivity data that point to monohydration for both metal ions in the dinuclear complex. A variable-temperature and -pressure 17O NMR study has been performed on [Mn2(ENOTA)(H2O)2] to assess the rate and, for the first time on a Mn2+ chelate, also the mechanism of the water exchange. The inner sphere water is slightly more labile in [Mn2(ENOTA)(H2O)2] (k298ex = 5.5 x 107 s-1) than in the aqua ion (2.1 x 107 s-1, Merbach, A. E.; et al. Inorg. Chem. 1980, 19, 3696). The water exchange proceeds via an almost limiting associative mechanism, as evidenced by the large negative activation volume (deltaV = -10.7 cm3 mol-1). The proton relaxivities measured on [Mn2(ENOTA)(H2O)2] show a low-field dispersion at approximately 0.1 MHz arising from a contact interaction between the MnII electron spin and the water proton nuclear spins.

A novel 8-carboxyindeno[1,2-b]quinoxalin-11-one thiosemicarbazone zinc(II) Schiff base complex

In the novel title binuclear zinc(II) Schiff base complex, bis(mu-11-thiosemicarbazonoindeno[1,2-b]quinoxaline-8-carboxylato)bis[(dimethyl sulfoxide)zinc(II)] dimethyl sulfoxide trisolvate, [Zn2(C17H9N5O2S)2(C2H6OS)2].3C2H6OS, each ZnII atom is five-coordinated and situated in a distorted square-pyramidal environment, coordinated by two L2- ligands and one dimethyl sulfoxide molecule. Each L2- ligand, which coordinates to two ZnII atoms, has two parts. One part, acting in a tridentate chelating mode, coordinates to one ZnII atom through two N atoms and one S atom, while another part coordinates to another ZnII atom through a monodentate carboxylate group. The whole complex has a dimeric structure. The coordination mode of the nearly planar L2- ligand is quite different from the most common mode for Schiff bases.

Saturated and unsaturated nickelalactones with N-heterocyclic carbene ligands: Synthesis and structures

Monomeric and dimeric nickelalactones with N-heterocyclic carbene ligands [(py)(im mes )Ni(CH 2CH 2COO)] ( 1), [(im mes )Ni(CH 2CH 2COO)] 2 ( 2), [(im t-but )Ni(C(Et) C(Et)-COO)] 2 ( 3), [(im mes )Ni(C(Et) C(Et)-COO)] 2 ( 4), and [(im mes )Ni(CH 2 C(CH 3) C(CH 3)-CH 2-COO)] ( 5) (im mes : 1,3-dimesityimidazol-2-ylidene; im t-but : 1,3-di- t-butylimidazol-2-ylidene) were synthesized and investigated by 1H, 13C NMR and IR spectroscopic measurements. The solid-state structures of 1– 3 and 5 were also elucidated by X-ray diffraction analyses of single crystals. In the compounds the Ni(II) ion has square-planar geometry. The metal centers in the dimers 2 and 3 are bridged by two endocyclic oxygen donor atoms of the carboxylate groups resulting in Ni 2O 2-four-membered rings. Reaction of [ ( im 2 mes ) Ni with 2,3-dimethylbutadiene and CO 2 resulted in an oxidative coupling of the two dienes followed by insertion of CO 2 to form the dimeric complex 6. The X-ray structure of 6 shows two substituted heptenoic acid dianions which connect the two Ni(II) centers. Each nickel atom is surrounded by a η 3-allyl group, a monodentate carboxylate group and an im mes ligand.

Chiral Molecular Magnets: Synthesis, Structure, and Magnetic Behavior of the Series [M(L‐tart)] (M = MnII, FeII, CoII, NiII; L‐tart = (2R,3R)‐(+)‐tartrate)

A new series of layered magnets with the formula [M(L-tartrate)] (M = Mn(II), Co(II), Fe(II), Ni(II); L-tartrate = (2R,3R)-(+)-tartrate) has been prepared. All of these compounds are isostructural and crystallize in the chiral orthorhombic space group I222, as found by X-ray structure analysis. Their structure consists of a three-dimensional polymeric network in which each metal shows distorted octahedral coordination bound to four L-tartrate ligands, two of which chelate through an alcohol and a carboxylate group and the other two bind terminally through a monodentate carboxylate group. The chirality of the ligand imposes a Delta conformation on all metal centers. Magnetically, the paramagnetic metal centers form pseudotetragonal layers in which each metal is surrounded by four other metals, with syn,anti carboxylate bridges. These salts show intralayer antiferromagnetic or ferromagnetic interactions, depending on the electronic configuration of the metal, and weak interlayer antiferromagnetic interaction. In all cases the magnetic properties are strongly affected by the anisotropy of the system, and the presence of magnetic canting has been found. The Mn derivative behaves as a weak ferromagnet with a critical temperature of 3.3 K. The Ni derivative shows very unusual magnetic behavior in that it exhibits antiferromagnetic ordering below 6 K, the onset of spontaneous magnetization arising from spin reorientation into a canted phase below 4.5 K, and a field-induced ferromagnetic state above 0.3 T at 2 K, behavior typical of metamagnets. The Fe and Co derivatives show antiferromagnetic interactions between spin carriers, but do not order above 2 K.

Poly[μ4-isonicotinato-μ3-nitrato-barium(II)

The title compound, [Ba(C6H4NO2)(NO3)] n , was formed by the hydrothermal reaction of Ba(NO3)2, isonicotinamide and KOH with release of ammonia. The Ba ion is ten-coordinated by nine O atoms and one N atom. Five of these O atoms derive from one monodentate and two bidentate nitrate anions. The other O atoms derive from one bidentate and two monodentate carboxylate groups of the isonicotinate anions. The coordination is completed by an N atom of the isonicotinate anion. These units are connected to form a three-dimensional framework structure.

Ethylenediamine- and propylenediaminediacetic acid derivatives as ligands for the “ fac-[M(CO) 3] +” core (M = Re, 99mTc)

The reaction of Re(CO) 5Cl with o- or p- N-(nitrophenyl)ethylenediaminediacetic acid (H 2L 1, H 2L 2) and o- or p- N-(nitrophenyl)propylenediaminediacetic acid (H 2L 3, H 2L 4) in methanol leads to the formation of stable anionic [Et 3NH][Re(CO) 3(L)] · H 2O complexes 1– 4. These compounds have been characterized by means of IR, mass spectrometry, elemental analysis, NMR and conductimetry, as well as X-ray crystallography for 2 and 3. The [Re(CO) 3] + moiety is coordinated via the nitrogen of the iminodiacetic acid unit and two oxygens of monodentate carboxylate groups. In each case, the nitro group of the aromatic ring remains uncoordinated. The analogous technetium-99m complexes 1′ and 3′ were also prepared quantitatively by the reaction of H 2L 1 and H 2L 3, respectively, with the fac-[ 99mTc(CO) 3(H 2O) 3] + precursor in ethanol. The corresponding Re and 99mTc compounds were shown to possess the same structure by means of HPLC studies. The high affinity of these ligands for the Tc(I) or Re(I) core, coupled with the easiness of their derivatization (by reduction of the nitro group in amino group), implies that the utilization of this ligand system to develop target-specific radiopharmaceuticals for diagnosis and therapy is promising.

Crystal of catena-(μ2-terephthalato)-bis (N-methylimidazole)-copper(II)

A new one-dimensional chain complex [Cu(ta) (N-MeIm)2]n (where ta = terephthalic acid dianion,N-MeIm =N-methylimidazole) has been synthesized and structurally characterized by single-crystal X-ray diffraction. The compound crystallizes in the Monoclinic space groupP21/c with the parameters:a = 5.2930(11)A,b = 14.679(3)A,c = 11.007(3)A, β = 104.84(3)∘,V = 826.7(3)A3, withZ = 4 formula units. In the structure, each Cu atom is coordinated by a pair ofN-methylimidazole ligands and a pair of monodentate carboxylate groups, affording a square planar N2O2 geometry. Both carboxylate groups of the terephthalate dianion coordinate in a monodentate mode bridging two Cu(II) ions with formation of 1D zigzag chain along thec axis. This supramolecular compound exhibits a three-dimensional solid state structure constituted by hydrogen bonds and C–H–π stacking interactions.

Crystal Structure and Characterization of Manganese(II) Carboxylates: 3D Metal−Organic Frameworks

Three mononuclear manganese (II) complexes with quinoline-2-carboxylate ion (quin-2-c), [Mn(quin-2-c)2(H2O)2]2·Hquin-2-c·2H2O (1), Mn(quin-2-c)2(EtOH)2 (2), and HbimH[Mn(quin-2-c)2Cl] (3) (HbimH+ = benzimidazolium ion), have been obtained by self-assembly and structurally characterized by X-ray diffraction. In all three complexes the quin-2-c ions are bound to manganese in the chelate mode through a ring nitrogen and a monodentate carboxylate group. In complexes 1 and 2 the manganese ions are coordinated in the distorted octahedron with an N2O4 donor set. In the complex anion Mn(quin-2-c)2Cl-, present in the crystal of 3, the manganese ion is five-coordinated by two quin-2-c ligands and the chlorine ion. The solid-state EPR spectra of 1 and 2 are characteristic of the Mn(II) ion in a distorted-octahedral geometry, whereas the spectrum of 3 is more complicated due to the zero-field splitting effect operating at lower symmetry. The EPR spectra of all complexes in frozen ROH are very similar and are characteristic of an octahedral environment around manganese. The systems of strong intermolecular hydrogen bonds form 1D structures in all complexes, which are further engaged in weak C−H···O, π···π and C−H···π interchain interactions, creating the 3D networks. The IR spectra reflect the differences in the hydrogen bond systems in 1−3.

Synthesis, crystal structures and IR spectra of isotypic pseudopolymorphs complexes of Zn(II) by indole-2-carboxylic acid and 2,9-dimethyl-1,10-phenanthroline with different solvates (DMA, DMF or DMSO)

Three ternary complexes of zinc indole-2-carboxylate (2-IC) with 2,9-dimethyl-1,10-phenanthroline (NC) in dimethylacetamide (DMA), dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) were synthesized, their X-ray crystal structure and IR spectra were determined. In compound [Zn(2-IC) 2(NC)]·(DMA) ( 1), Zn is five-coordinate by one bidentate NC ligand and two 2-IC anionic ligands one of which is monodentate, and the other is bidentate. The individual molecules are linked into chains running parallel to the a-axis by intermolecular hydrogen bonding. The crystal structure is completed by a DMA solvate molecule. Compounds [Zn(2-IC) 2(NC)]·(DMF) ( 2) and [Zn(2-IC) 2(NC)]·(DMSO) ( 3) contain one monomeric zinc complex similar to 1 and a disordered solvate molecule (DMF in 2; DMSO in 3) in contrast to 1. In the IR spectra of the three compounds, the most important feature is the appearance of a very broad band at about 3175 cm −1 presenting a fine structure which can be correlated to hydrogen bonds in N–H⋯O bifurcated links, via inter and intramolecular interactions. A tentative assignment was made to point out the bidentate or monodentate carboxylate groups attached to the Zn atom.

Aqua(2,2'-diamino-4,4'-bi-1,3-thiazole-kappa2N,N')(iminodiacetato-kappa3O,N,O')chromium(III) chloride monohydrate.

Crystals of the title compound, [Cr(C4H5NO4)(C6H6N4S2)(H2O)]Cl.H2O, consist of Cr(III) complex cations, Cl- counter-ions and lattice water molecules. The complex cation assumes an octahedral coordination geometry, formed by a tridentate iminodiacetate dianion (IDA), a diaminobithiazole (DABT) molecule and a water molecule. The planar DABT group chelates the Cr(III) ion with normal Cr-N distances [2.0574 (17) and 2.0598 (17) A], but the DABT molecule is inclined to the coordination plane by a dihedral angle of 17.23 (7) degrees. In the monodentate carboxylate groups of the IDA ion, the coordinated C-O bonds [1.288 (3) and 1.284 (3) A] are much longer than the uncoordinated C-O bonds [1.222 (3) and 1.225 (3) A].

Synthesis, structure and luminescent property of a binuclear terbium complex [Tb 2(Hsal) 8(H 2O) 2][(Hphen) 2]·2H 2O

A binuclear terbium complex [Tb 2(Hsal) 8(H 2O) 2][(Hphen) 2]·2H 2O 1 (Hsal= o-HOC 6H 4CO 2 −, phen=1,10-phenanthroline) was synthesized and characterized by elemental analysis, molar conductance, IR, UV–VIS, X-ray powder diffraction, Thermogravimetric analysis and fluorescence. Its structure was determined by X-ray single crystal diffraction. In the dimeric anion [Tb 2(Hsal) 8(H 2O) 2] 2−, two terbium atoms are connected by four bidentate bridging carboxylate groups. Each Tb atom is eight-coordinated to four bidentate bridging carboxylate groups, one bidentate chelating carboxylate groups, one monodentate carboxylate group as well as one water molecule. The mono-protonated phen does not coordinate to the Tb atom directly. Hydrogen bonds, π–π stacking interactions and electrostatic attractions result in the formation of a two-dimensional supramolecular structure. The solid-state luminescence behavior of 1 was studied. Compared with binary terbium salicylate Tb(Hsal) 3(H 2O) 2·2H 2O, it emits a relatively weak green light under the excitation of UV light, which may be attributed to the formation of extensive π-electron conjugation systems in the structure.

Selective recognition of configurational substates of zinc cyclam by carboxylates: implications for the design and mechanism of action of anti-HIV agents.

The interaction of metal cyclams with carboxylate groups is thought to play an important role in their binding to the CXCR4 chemokine receptor and in their anti-HIV activity. Here we report the synthesis of acetate, phthalate, perchlorate and chloride complexes of Zn(II) cyclam (1,4,8,11-tetraazacyclotetradecane). The X-ray crystal structures of [Zn(cyclam)(phthalate)](n)(CH(3)OH)(2n) and [Zn(cyclam)(H(2)O)(2)](OAc)(2) contain octahedral Zn(II) centres. Phthalate acts as a bridging ligand in the former complex, binding through monodentate carboxylate groups, and giving rise to infinite chains in the lattice together with extensive hydrogen bonding between carboxylate donor oxygen atoms and amine and methanol acceptor atoms. The uncoordinated acetate groups and the aqua ligand in the acetate complex are also involved in a rich network of hydrogen bonds and this may account for the unusually long Zn[bond]O distance (2.27 A). In both crystalline complexes, the macrocycle adopts the trans-III (S,S,R,R) configuration. 1D (1)H NMR spectra of all four complexes have been fully assigned by a combination of 2D [(1)H, (1)H] COSY and TOCSY, and [(1)H, (13)C] and [(1 )H, (15)N] HSQC NMR data. In aqueous solution, the stable trans-III configuration found in the solid-state equilibrates slowly (hours at 298 K) with trans-I (R,S,R,S) and cis-V (R,R,R,R) configurations. The trans-III configuration is predominant in aqueous solution for both the chloride and perchlorate complexes, but for the acetate and phthalate complexes, the cis-V configuration dominates. Carboxylate groups appear to stabilize the cis-V configuration in solution through Zn(II) coordination and hydrogen bonding. Titration of the chloride Zn(II)-cyclam complex with acetate confirmed that carboxylates strongly induce formation of the cis-V configuration. This implies that carboxylates can exert a strong influence over configurational selectivity. Cyclam NH hydrogen bonding is prevalent both in the solid state and in solution, and is relevant to the anti-HIV activity of Zn(II) and other metal cyclam complexes and to their ability to recognize the CXCR4 transmembrane co-receptor.

Crystal structure and properties of complex [Eu(m-BrBA) 3(H 2O)(phen)] 2

A binuclear europium complex [Eu(m-BrBA) 3(H 2O)(phen)] 2 (1) has been obtained in the ethanol solution and characterized structurally by X-ray diffraction, where m-BrBA=m-bromobenzoate and phen=1,10-phenanthroline. Each Eu 3+ ion is eight-coordinated to one 1,10-phenanthroline molecule, one monodentate carboxylate group, one water molecule and four bridging carboxylate groups in which the carboxylate groups are bonded to the europium ion in two modes: the monodentate and the bridging bidentate. Excitation and luminescence data observed at room temperature show that the title complex emits red fluorescence under ultraviolet light. The results of thermal analysis indicate that the complex [Eu(m-BrBA) 3(H 2O)(phen)] 2 is quite stable to heat.

Tetrakis[(4-aminopyridinio)acetato-kappa O]diaquamanganese(II) diperchlorate.

In the centrosymmetric title complex, [Mn(C(7)H(8)N(2)O(2))(4)(H(2)O)(2)](ClO(4))(2), the Mn(II) ion is in an octahedral environment, with the equatorial plane being defined by the O atoms of four monodentate carboxylate groups, and the octahedron being completed by two trans-coordinated water molecules. There are intramolecular hydrogen bonds between the coordinated water molecules and the non-coordinated O atoms of the carboxylate groups. Hydrogen bonds between the amino groups and the carboxylate groups of neighbouring molecules generate a layered hydrogen-bonded network.

Self-assembly of silver(i) coordination polymers with novel layered open network structures based on a flexible double betaine ligand

Three coordination polymers, [Ag4(L1)2(NO3)4]·H2O (1), [Ag(L1)](BF4)·2H2O (2) and [Ag2(L1)(H2O)](ClO4)2 (3), were obtained from self-assembly of AgX (X = NO3−, BF4−, or ClO4−) with a new flexible double betaine L1 (L1 = 1,3-bis(pyridinio-4-carboxylato)propane). Single crystal X-ray diffraction studies for complexes 1–3 reveal layered open network structures containing novel cavities and channels. Complex 1 consists of an unprecedented rhombic tetrameric Ag4O2 subunit, in which a μ3-η1 coordination mode of the carboxylate group is found for the first time among silver(I) carboxylates. Complex 2 is constructed from a bis(carboxylate-O,O′)-bridged centrosymmetric dimeric subunit, in which the coordination sphere of each silver(I) atom is completed by a monodentate carboxylate group at each axial site. In complex 3, the [Ag2(carboxylate-O,O′)2] dimeric subunits are extended into a polymeric chain through the linkage of each metal centre to carboxylate groups of an adjacent dimer, and such infinite chains are extended into a plane wave-like layer structure by the cross-linkage of the molecular skeletons of the flexible double betaine ligands.