PREPARATION AND PROPERTIES OF PYRIDINE DICARBOXYLIC ACID COMPLEXES OF THE LANTHANIDES

Abstract

The preparation and spectroscopic properties of eleven hydrated lanthanide (III) dipicolinate and quinolinate complexes are reported for the first time. The complexes are of three general types: M(dipi)(dipiH)(H₂O)₄, M(dipiH)₃(H₂O) and M(quin)(quinH)(H₂O)₃ [where M =lanthanide (III); dipiH₂ =pyridine-2,6-dicarboxylic acid (dipicolinic acid); quinH₂ =pyridine-2, 3-dicarboxylic acid (quinolinic acid)], and evidence is presented which indicates that they may be six-coordinate.     

Crystal structure,bioactivities, and electrochemistry properties of four diverse complexes with a new pyrazole ligand

Four complexes, [Cu(cmpa)(Hpdbl)] ? 2H₂O (1), [Cd(cmpa)₂] ? 2.5H₂O (2), [Cu(cmpa)₂] ? 2.5H₂O (3), and [Pb(cmpa)₂] · 2.5H₂O (4), have been synthesized and characterized based on the pyrazole ligand (Hcmpa = 3-chloro-6-(3,5-dimethy-1-yl)picolinic acid, H₂pdbl = pyridine-2,6-dicarboxylic acid). Complexes 1–4 showed 3-D supramolecular architectures that are connected through hydrogen bonds and aromatic π–π interactions. Preliminary antibacterial activities of the complexes indicated selective inhibition for the tested strains. The electrochemistry of 1–4 was studied by cyclic voltammetry in DMSO using a glassy carbon working electrode.     

A series of Cd(II) complexes with π-π stacking and hydrogen bonding interactions: Structural diversities by varying the ligands

Seven new Cd(II) complexes consisting of different phenanthroline derivatives and organic acid ligands, formulated as [Cd(PIP)₂(dnba)₂] (1), [Cd(PIP)(ox)]·H₂O (2), [Cd(PIP)(1,4-bdc)(H₂O)]·4H₂O (3), [Cd(3-PIP)₂(H₂O)₂]·4H₂O (4), [Cd₂(3-PIP)₄(4,4′-bpdc)(H₂O)₂]·5H₂O (5), [Cd(3-PIP)(nip)(H₂O)]·H₂O (6), [Cd₂(TIP)₄(4,4′-bpdc)(H₂O)₂]·3H₂O (7) (PIP=2-phenylimidazo[4,5-f]1,10-phenanthroline, 3-PIP=2-(3-pyridyl)imidazo[4,5-f]1,10-phenanthroline, TIP=2-(2-thienyl)imidazo[4,5-f]1,10-phenanthroline, Hdnba=3,5-dinitrobenzoic acid, H₂ox=oxalic acid, 1,4-H₂bdc=benzene-1,4-dicarboxylic acid, 4,4′-H₂bpdc=biphenyl-4,4′-dicarboxylic acid, H₂nip=5-nitroisophthalic acid) have been synthesized under hydrothermal conditions. Complexes 1 and 4 possess mononuclear structures; complexes 5 and 7 are isostructural and have dinuclear structures; complexes 2 and 3 feature 1D chain structures; complex 6 contains 1D double chain, which are further extended to a 3D supramolecular structure by π-π stacking and hydrogen bonding interactions. The N-donor ligands with extended π-system and organic acid ligands play a crucial role in the formation of the final supramolecular frameworks. Moreover, thermal properties and fluorescence of 1-7 are also investigated.     

Syntheses and characterizations of four metal coordination polymers constructed by the pyridine-3,5-dicarboxylate ligand

A series of metal-organic frameworks, namely [Ni(PDB)(H₂O)]_n (1), [Pb(PDB)(H₂O)] · (H₂O) (2), [Co₂(PDB)₂(bpy)₂(H₂O)₄] · 4H₂O (3) and [Co₂(PDB)₂(phen)₂]_n (4) (H₂PDB = pyridine-3,5-dicarboxylic acid, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline), have been synthesized based on pyridine-3,5-dicarboxylate acid and two neutral chelate ligands, with different metal ions such as Ni^II, Co^II and Pb^II, under hydrothermal conditions. The framework structures of these polymeric complexes have been determined by the X-ray single crystal diffraction technique. In the four complexes, the pyridine-3,5-dicarboxylate acid ligand exhibits diverse coordination modes, which play an important role in the construction of metal-organic frameworks. The thermal analyses of these four complexes have been measured and discussed. In addition, complex 2 shows strong phosphorescent emission at room temperature and the magnetic measurement of the polymer of 4 reveals a typical antiferromagnetic exchange.     

An evaluation of primary water standards by TG/DTA and vapor sorption analysis

The thermal behavior of [Ca(H₂O)₃(2,3-pydcH)₂] _n (I), [Cd(H₂O)₃(2,3-pydc)] _n (II), and [Cd(H₂O)₆][Cd(2,3-pydcH)₃]₂ (III) complexes with pyridine-2,3-dicarboxylic acid was monitored by TG, DTG, and DSC analysis, where 2,3-pydcH—mono deprotonated pyridine-2,3-dicarboxylic acid and 2,3-pydc—doubly deprotonated dicarboxylate anion. Thermal decomposition of these compounds go through one or two dehydratation stages, followed by the loss of organic matter. The final decomposition products are found to be the corresponding metal oxides. The possible scheme of destruction of the complexes have been used to reveal the relationships between stability and molecular structure.     

Novel coordination compounds of quinic acid. X-ray diffraction study of copper(II) complexes where the metal ion was a chiral centre

Summary The synthesis and characterization of the following coordination compounds derived from quinic acid (quin) (1): [Cu(quin)Cl(H₂O)]_n·(H₂O)_n(2); [Ni(quin)Cl(H₂O)]_n·(2H₂O) n (3); [Co(quin) Cl(H₂O)]_n·(2H₂O)_n(4); [Cu(quin) (NO₃)(H₂O)]_n·(2H₂O)_n(5); [Cu(quin)(AcO)(H₂O)]_n· (2H₂O)_n(6); [Cu(quin)H₂O]₂·2H₂O(7); [Co(quin)₂]_n (8); [Zn(quin)₂](9); [Cd(quin)₂](10) and [Hg(quin)₂]· 4H₂O (11) is presented. All of the compounds were characterized by i.r. and u.v. spectroscopy; in addition, (9) and (10) were analysed by n.m.r., and (2), (5) and (7) by X-ray crystallography. Due to the polyfunctionality of quinic acid diverse structures were obtained: (2) –(6) and (8) were polymeric, (7) was dimeric and (9) –(11) were spiranic. In compound (2) the Cu had a distorted octahedral structure; it was a chiral centre with six different substituents and an optically active ligand. Only one stereoisomer (OC-6-25-A) of the 30 possible was observed in the crystal. Compound (5) was also polymeric, the hexacoordinated Cu atom was a chiral centre (OC-6-53C) and only one stereoisomer was observed. It was bonded to three quinic acid ligands in three different coordination modes and each quinic acid was in turn bonded to three different Cu atoms. Each chain was linked to another two chains giving a net structure. Compound (7) was a dimer with two square pyramidal Cu atoms. Two apical water molecules were found in acis arrangement. Each quinic acid ligand was bonded to two Cu atoms which were linked by two oxygen bridges and each Cu atom was bonded to two quinic acid moieties.     

A 3-D pillar-layered coordination polymer {[EuCu(C2O4)(na)2] · 2H2O} n : synthesis,structure and photoluminescent properties

A 3d–4f heterometallic coordination polymer, {[EuCu(C₂O₄)(na)₂] ·?2H₂O} _n (1) [Hna=nicotinic acid], has been synthesized by hydrothermal reaction of lanthanide oxides, Cu(I), and pyridine-2,3-dicarboxylic acid. 1 features a 3-D pillar-layered coordination framework constructed from two-dimensional lanthanide-carboxylate layers and Cu(na) pillars. Interestingly, the na ligand was obtained by the in situ decarboxylation of pyridine-2,3-dicarboxylic acid.     

Preparation and characterization of some pyridine-2,6-dicarboxylato thorium(IV) complexes

Summary The preparation of complexes of pyridine-2,6-dicarboxylic acid (H₂PDC) with thorium(IV) is reported and discussed. The reactivity of Th(PDC)₂ (H₂O)₄ (1) was tested by preparing adducts with some neutral ligands. The complexes were characterized by i.r. spectroscopy, elemental analysis and thermal behaviour. Preliminary information on the structure of(1) obtained by x-ray analysis, are also reported.Author to whom all correspondence should be directed.     

Complexes of NS and NSO donor ligands. Nickel(II), copper(II) and cobalt(II) complexes of glyoxal bis(morpholineN-thiohydrazone) and diacetyl bis(morpholineN-thiohydrazone)

Summary Reactions of glyoxal bis(morpholineN-thiohydrazone), H₂gbmth, with NiCl₂·6H₂O, Ni(OAc)₂·4H₂O, Ni(acac)₂· H₂O, CuCl₂·2H₂O, Cu(OAc)₂·H₂O, Cu(acac)₂, CoCl₂· 6H₂O, Co(OAc)₂·4H₂O and Co(acac)₂·2H₂O yield complexes of the type [M(gbmth)], [M=Ni^II, Cu^II or Co^II]. Diacetyl reacts with morpholineN-thiohydrazide in the presence of nickel salts to yield [Ni^II(dbmth)], [Ni^II(dmth)(OAc)]H₂O and [Ni^II(Hdmth)(NH₃)Cl₂] involving N₂S₂ and NSO donor ligands. Copper and cobalt complexes of N₂S₂ and NSO donor ligands with compositions [Cu^II(dbmth)], [Co^II(dbmth)]·4H₂O and [Co^II(H₂dbmth)]Cl₂, have been isolated. The compounds have been characterised by elemental analyses, magnetic moments, molar conductance values and spectroscopic (electronic and infrared) data.     

Syntheses and characterization of three lanthanide(III) complexes containing pyridine-3,5-dicarboxylic acid and oxalic acid ligands

Direct reaction of pyridine-3,5-dicarboxylic acid (H₂PDA) and oxalic acid (H₂ox) with Ln(ClO₄)₃ · nH₂O under hydrothermal conditions gave three 3-D coordination networks, [Ln(PDA)(ox)_0.5(H₂O)₂] · H₂O [Ln = La(1), Nd(2), and Eu(3)]. The complexes were characterized by elemental analysis (EA), X-ray single-crystal diffraction, infrared spectroscopy (IR), and thermogravimetric analysis (TGA). Single crystal X-ray diffractions shows that the compounds are isomorphous and have 3-D framework structures, in which pyridine-3,5-dicarboxylates (PDA^2?) link lanthanides to give 2-D layers, which are further fabricated into a 3-D network via bis-bidentate oxalate bridging. Luminescence of 3 is investigated.     

Thermoanalytical studies of oxovanadium(IV)hydroxamate complexes

The thermal decomposition behavior of oxovanadium(IV)hydroxamate complexes of composition [VO(acac)(C₆H₅C(O)NHO)] (I), [VO(C₆H₅C(O)NHO)₂] (II), [VO(acac)(4-ClC₆H₄C(O)NHO)] (III), [VO(4-ClC₆H₄C(O)NHO)₂] (IV) (where acac = (CH₃COCHCOCH₃ ^–) synthesized from the reactions of VO(acac)₂ with equi- and bimolar amounts of potassium benzohydroxamate and potassium 4-chlorobenzohydroxamate in THF + MeOH solvent medium has been studied by TG and DTA techniques. TG curves indicated that complexes I, II, and IV undergo decomposition in single step to yield VO₂ as the final residue, while complex III decomposes in two steps to yield VO(acac) as the likely intermediate and VO₂ as the ultimate product of decomposition. The formation of VO₂ has been authenticated by IR and XRD studies. From the initial decomposition temperatures, the order of thermal stability for the complexes has been inferred as IV > I > III > II.     

One-dimensional coordination polymers of praseodymium(III)–vanadium(V) complexes with pyridine-2,6-dicarboxylic acid

This paper represents the hydrothermal synthesis of new isomorphous lanthanide–vanadium complexes with one-dimensional coordination polymers: [Pr₂(VO₂)₂(dipic)₄(H₂O)₉] · nH₂O with dipic = pyridine-2,6-dicarboxylic acid and n = 7.75. The structure determination shows a unique one-dimensional structure in which three types of chains run along the c-axis: the chain of positively charged praseodymium complexes bridged by a dipic ligand ([Pr(dipic)(H₂O)₅]⁺), the chain of negatively charged, stacked vanadium complexes ([VO₂(dipic)]⁻), and the chain of neutral praseodymium complexes with a bridged dipic ligand and a coordinating dipic ligand ([Pr(dipic)[VO₂(dipic)](H₂O)₄]). Such one-dimensional chains provide open channels which can accommodate water molecules. Not only accommodated water molecules but also ones coordinated to praseodymium ions were easily removed and absorbed upon heating at 200 °C and exposure of humidity at room temperature, respectively.     

Cobalt(II) and nickel(II) complexes with 4-amino-6-methyl-5-oxo-3-phenylamino-1,2,4-triazine

Summary Cobalt(II) and nickel(II) complexes of 4-amino-6-methyl-5-oxo-3-phenylamino-1,2,4-triazine (ATAZ), MX₂(ATAZ)₂ · 2 H₂O (M = Co or Ni; X = Cl, Br, I or NCS), have been isolated. The electronic spectra, magnetic moments and i.r. spectra of the compounds have been studied.Pseudo-octahedral environments are proposed for the complexes: [MX₂(ATAZ)₂]. 2 H₂O (M = Ni or Co; X = Cl or Br) and [CoI₂(ATAZ)₂(H₂O)₂], and apseudo-tetrahedral structure for [NiX₂(ATAZ)₂] · 2 H₂O (X = I or NCS) and [Co(NCS)₂-(ATAZ)₂] · 2 H,O. However, [CoX₂(ATAZ)₂]. 2 H₂O (X = Cl or Br) give acetone solutions containing tetrahedral cobalt(II).     

Synthesis,spectral and EPR studies of oxovanadium(IV) complexes incorporating tridentate ONO donor hydrazone ligands: Structural study of one oxovanadium(V) complex

Five oxovanadium(IV) complexes of 2-hydroxy-4-methoxybenzaldehyde nicotinic acid hydrazone (H₂L¹), 2-hydroxy-4-methoxyacetophenone nicotinic acid hydrazone (H₂L²) and a binuclear oxovanadium(V) complex of H₂L² have been synthesized. These complexes were characterized by different physicochemical techniques like electronic, infrared and EPR spectral studies. The complexes [VOL¹]₂ · H₂O (1) and [VOL²]₂ · H₂O (4) are binuclear and [VOL¹bipy] (2), [VOL¹phen] · 1.5H₂O (3) and [VOL²phen] · 2H₂O (6) are heterocyclic base adducts and are EPR active. In frozen DMF at 77 K, all the oxovanadium(IV) complexes show axial anisotropy with two sets of eight line patterns. The complex [VOL² · OCH₃]₂ (5) is an unusual product and has distorted octahedral geometry, as obtained by X-ray diffraction studies.     

Metal–organic polymers of Sr(II) and Ce(IV): structural studies,supramolecular synthons,and potentiometric measurements

Two metal–organic coordination polymers based on a salt, (pydcH)₃·(pipzH₂)_1.5·(H₂O)_3.7, between pyridine-2,6-dicarboxylic acid, pydcH₂, and piperazine, pipz, formulated as (pipzH₂)[Sr(pydc)₂(H₂O)₂]_n·4H₂O and [Ce(pydc)₂(H₂O)₂]_n·4H₂O were prepared. The synthesis, IR spectroscopy, elemental analysis, single-crystal X-ray diffraction, supramolecular synthons, and potentiometric measurements were investigated. The chemical environment around each Sr(II) or Ce(IV) was a distorted tricapped trigonal prism. The butterfly- and ladder-like structures of these complexes were bridged by oxygens of (pydc)^2– and M–O(pydc)–M bonds. In the crystal structure, intermolecular O–H?O, N–H?O, and C–H?O hydrogen bonds result in the formation of supramolecular structures. The stoichiometry and stability of the pydc–pipz system with Sr(II) in aqueous solution were investigated by potentiometric titration. The stoichiometry of complex species in solution was found to be similar to the cited crystalline metal ion complexes.     

Syntheses, structures and properties of 3D inorganic-organic hybrid frameworks constructed from lanthanide polymer and Keggin-type tungstosilicate

Inorganic-organic hybrid frameworks, namely [Ce(H₂O)₃(pdc)]₄[SiW₁₂O₄₀]·6H₂O 1, [M(H₂O)₄(pdc)]₄[SiW₁₂O₄₀]·2H₂O (M=Ce for 2a, La for 2b, Nd for 2c; H₂pdc=pyridine-2,6-dicarboxylic acid) were assembled through incorporation of Keggin-type heteropolyanion [SiW₁₂O₄₀]⁴⁻ within the voids of lanthanides-pdc network as pillars or guests under hydrothermal condition. Single-crystal X-ray analyses of these crystals reveal that compound 1 presents 3D pillar-layered framework with the [SiW₁₂O₄₀]⁴⁻ anions located on the square voids of the two-dimensional Ce-pdc bilayer. Compounds 2a-c are isostructural and constructed from 3D Ln-pdc-based metal-organic framework (MOF) incorporating noncoordinating guests Keggin structure [SiW₁₂O₄₀]⁴⁻. Solid-state properties of compounds 1 and 2a-c such as thermal stability and photoluminescence have been further investigated.     

Übergangsmetallkomplexe der Pyrazin-2,6-dicarbonsäure und der Pyridin-2,6-dicarbonsäure: Synthesen und Elektrochemie. Die Kristallstruktur von NH4[RuCl2(dipicH)2]

Transition Metal Complexes Containing the Ligands Pyrazine-2, 6-dicarboxylate and Pyridine-2, 6-dicarboxylate: Syntheses and Electrochemistry. Crystal Structure of NH₄[RuCl₂(dipicH)₂] The coordination chemistry of the tridentate ligand pyrazine-2, 6-dicarboxylate (pyraz-2,6 = L) with transition metals in aqueous solution has been investigated. The reaction of the ligand with metal aqua ions (1:1) affords insoluble precipitates [M^IIL(OH₂)₂] (M = Mn, Fe, Co, Ni, Cu, Zn, Cd). [TiOL(OH₂)₂], [VOL(H₂O)₂] and [UO₂L(H₂O)] were also prepared. [M^IIIL₂]^? complexes (M^III ? Fe^III, Co^III) were isolated as NH₄⁺ and P(C₆H₅)₄⁺ salts; they are strong one electron oxidants (E_1/2 = +0.602 V and +0.795 V vs. NHE, respectively). Redox potentials of analogous complexes containing pyridine- 2, 6-dicarboxylate (L′) ligands have been determined by cyclic voltammetry: [ML′₂]^1-/2?: M = V^III: -0.591 V; Cr^III: -0.712 V. It is shown that pymzine-2,6-dicarboxylate as compared to pyridine-2,6-dicarboxylate stabilizes metal complexes in low oxidation states (+II). The reaction of RuCl₃ · nH₂O with pyridine-2,6-dicarboxylic acid in aqueous solution affords the yellow-green anion [RuCl₂(L′H)₂]^?. The crystal structure of NH₄[RuCl₂(L′H)₂] has been determined. It crystallizes in the monoclinic space group P2₁/c with a = 8.812(2) Å b = 10.551(2) Å, c = 10.068(2) Å, β = 110.03(6)°, Z = 2; 2507 independent reflections; R = 0.032. The ruthenium centers are in an octahedral environment of two Cl^? ligands (trans) and two bidentate pyridine-2, 6-hydrogendicarboxylate ligands which possess each one protonated, uncoordinated carboxylic group.     

Synthesis, spectral and X-ray structural studies of Ni(II) complexes of N′-acylhydrazine carbodithioic acid esters containing ethylenediamine or o-phenanthroline as coligands

The new complexes [Ni(Hbstbh)₂(en)] (1) and [Ni(Hpchce)(o-phen)₂]Cl·CH₃OH·H₂O (2) with N′-benzoyl hydrazine carbodithioic acid benzyl ester (H₂bstbh) and [N′-(pyridine-4-carbonyl)-hydrazine]-carbodithioic acid ethyl ester (H₂pchce) have been synthesized, containing ethylenediamine (en) or o-phenanthroline (o-phen) as coligands. The ligands and their complexes have been characterized by elemental analyses, IR, magnetic susceptibility and single crystal X-ray data. [Ni(Hbstbh)₂(en)] (1) and [Ni(Hpchce)(o-phen)₂]Cl·CH₃OH·H₂O (2) crystallized in the monoclinic and triclinic systems, space group C2/c and P-1, respectively. The (N, O) donor sites of the bidentate ligands chelate the Ni(II) center and form a five-membered CN₂ONi ring. The resulting complexes are paramagnetic and have a distorted octahedral geometry.     

Syntheses,crystal structures,and luminescence of carboxylato-bridged coordination compounds

Two 2-D metal carboxylate coordination compounds [Tb(pydc)(ox)_1/2(H₂O)₂] (1) and [Cd(pydc)(me)(H₂O)]₂ · H₂O (2) (pyridine-2,5-dicarboxylic acid = pydc, oxalic acid = ox, me = methanol) have been synthesized under hydrothermal conditions. Carboxylates are building blocks in the formation of zigzag chain and cockle stair-like chain structures for 1 and 2, respectively. Both the compounds have been structurally determined by single-crystal X-ray diffraction, and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and fluorescence spectra.