Neutral Tetradentate Ligand Research Articles

Construction of a series of metal–organic frameworks with a neutral tetradentate ligand and rigid carboxylate co-ligands

The solvothermal reaction of a neutral tetradentate ligand, different bivalent metal salts and two rigid carboxylate co-ligands gave six metal–organic frameworks (MOFs): [Zn(L)(Hbdc)(bdc)0.5]·1.5H2O (1), [Zn2(L)(bdc)2(H2O)]·2H2O (2), [Cd(L)(bdc)(H2O)]·2H2O (3), [Ni(L)(bdc)(H2O)]·H2O (4), [Co3(L)(btc)2(H2O)4] (5), [Zn3(L)(btc)2(H2O)4] (6) (L = 1,1′-oxybis[3,5-dipyridine]-benzene, H2bdc = 1,4-benzenedicarboxylate, H3btc = 1,3,5-benzenetricarboxylate). Compounds 1 and 2 have been co-crystallized in a one-pot reaction. In compound 1, L and H2bdc ligands link Zn centers to generate a two-dimensional (2D) sheet structure which is further connected by intermolecular hydrogen bonds to form a 3-fold interpenetrating 3D fsc-3,4-C2/c array. Single crystal X-ray diffraction analysis reveals that compound 2 features a 3D self-interpenetrated network with {4·6·83·10}{4·63·82}{64·82} topology. For compounds 3 and 4, the binuclear metal secondary building unit (SBU) assembles with mixed ligands, L and H2bdc, to construct a 3D α-Po structure. Compounds 5 and 6 are isostructural and show 3-fold interpenetrated pte/Cmmm->P2/c structures.

Polymeric and sandwich Schiff’s bases complexes derived from 4,4′-methylenedianiline

Cobalt(II), nickel(II) and copper(II) complexes of Schiff’s bases derived from 4,4′-methylenedianiline and pyridine-2-carboxaldehyde(L1), furan-2-carboxaldehyde(L2) or thiophene-2-carboxaldehyde(L3), were prepared and characterized by different analytical and spectral methods. The Schiff bases behave as neutral tetradentate ligands. The chloro-complexes of (L2) with (2:3) mole ratio have a polymeric nature. However, that of L1 and L3 with (1:1) mole ratio showed a sandwich structure. All complexes display an octahedral geometry, except complex (2) which has a tetrahedral one. O h/T d equilibrium for chloro-complexes of cobalt with ligand L1 was established in the solid state. ESR spectra of solid copper(II) complexes showed isotropic and axial type with dx 2-y 2 ground state. The thermal study showed that the complexes with different solvents of crystallization exercise different types of interaction. The observed thermochromic phenomenon for cobalt complex was explained along with its thermal behaviour.

Zn(II) complex-based potentiometric sensors for selective determination of nitrate anion

Polymeric membranes containing new Zn(II) complexes as anion carriers were prepared for determination of nitrate anion present in water samples. Two Zn(II) complexes coordinated by neutral tetradentate ligands, N,N′-ethylene-bis( N-methyl-( S)-alanine methylamide) and N,N′-ethylene-bis( N-methyl-( S)-alanine dimethylamide), worked well as anion-selective carriers, while common phthalocyanine Zn(II) complex rarely responded to any anions. The combination of these new Zn(II) complexes with dioctylsebacate as a plasticizer particularly offered high sensing selectivity for nitrate anion. They exhibited near-Nernstian slopes in the wide linear concentration range of 5.0 × 10 −5 to 1.0 × 10 −1 M, and operated well in the wide pH range from 4 to 11 with the response time of less than 25 s. The potentiometric selectivity coefficients were evaluated using the fixed interference method, indicating that the two Zn(II) complexes exhibited better selectivity for nitrate anion with respect to a wide variety of inorganic anions. Although chloride anion worked as an interfering species at a concentration higher than 1.0 × 10 −3 M, the new Zn(II) complex-based sensors were applicable in determination of the nitrate anion after adding silver sulfate to remove the chloride anion.

Synthesis and crystal structure of a copper(II) complex of the tripodal tetradentate ligand tris(2-benzimidazolylmethyl)amine

A mononuclear copper complex [Cu(NTB)Cl]Cl·3CH3CH2OH (1) (NTB = tris(2-benzimidazolylmethyl)amine) was synthesized and its structure was determined by single crystal X-ray diffraction. In this complex, copper(II) is five-coordinate with NTB serving as a neutral tetradentate ligand. Three tertiary nitrogen atoms of benzimidazole groups of NTB formed the base of the trigonal bipyramidal geometry. One axial position was occupied by the apical nitrogen atom of NTB and the other was occupied by chloride. The ESR spectrum of complex 1 in ethanol at 101 K was recorded and the well-defined ESR parameters (g ∥ = 2.02, g ⊥ = 2.16 and A ∥ = 109 G) indicated that the Cu(II) has a distorted trigonal-bipyramidal environment, in good agreement with crystal structure determination for complex 1.

Cadmium(II) Complexes of 1,2-Di(Imino- 4′-Antipyrinyl)Ethane

Cadmium(II) complexes of the Schiff base 1,2-di(imino-4′-antipyrinyl)ethane (GA) having general formulae [Cd(GA)]X2; (X=NO3 −, ClO4 −) and [Cd(GA)X2]; (X=Cl−, Br− or I−) have been synthesized and characterized by elemental analysis, electrical conductance in non-aqueous solvents, infrared and electronic spectra as well as thermogravimetric analysis. In all these complexes, GA acts as a neutral tetradentate ligand coordinating through both the carbonyl oxygens and both the azomethine nitrogens. Both the anions are coordinated in the halide complexes while these remain as counter ions in the perchlorate and nitrate complexes. Thermal decomposition behavior of the nitrate complex indicates that it is stable up to 234 °C and undergoes a three-stage decomposition pattern yielding the anhydrous Cadmium(II) oxide as the final residue.

Structural Insights into Nonheme Alkylperoxoiron(III) and Oxoiron(IV) Intermediates by X-ray Absorption Spectroscopy

Transient mononuclear low-spin alkylperoxoiron(III) and oxoiron(IV) complexes that are relevant to the activation of dioxygen by nonheme iron enzymes have been generated from synthetic iron(II) complexes of neutral tetradentate (TPA) and pentadentate (N4Py, Bn-TPEN) ligands and structurally characterized by means of Fe K-edge X-ray absorption spectroscopy (XAS). Notable features obtained from fits of the EXAFS region are Fe-O bond lengths of 1.78 A for the alkylperoxoiron(III) intermediates and 1.65-1.68 A for the oxoiron(IV) intermediates, reflecting different strengths in the Fe-O pi interactions. These differences are also observed in the intensities of the 1s-to-3d transitions in the XANES region, which increase from 4 units for the nearly octahedral iron(II) precursor to 9-15 units for the alkylperoxoiron(III) intermediates to 25-29 units for the oxoiron(IV) species.

Synthesis, characterization, and crystal structure of 1,4-bis(3-aminopropyl)piperazineperchloratocopper(II) perchlorate

The complex [Cu(C10H24N4)(ClO4)]ClO4, where C10H24N4=1,4-bis(3-aminopropyl)piperazine was synthesized and characterized, and its molecular structure was established by X-ray diffraction. The complex crystallizes in orthorhombic Pbca (no. 61) with Z=8, a=14.417(3) Å, b=15.067(3) Å, and c=16.101(3) Å. The structure consists of isolated [Cu(C10H24N4)(ClO4)]+ cations and perchlorate counter anions. The coordination geometry of the Cu(II) center may be described as square pyramidal (SP) with ClO4− group at the apical site and the N donor atoms of the neutral tetradentate ligand occupy the basal sites. The Cu–N bond distances are 2.069(4), 2.020(3) Å for the internal chelate rings, and 2.033(4) and 1.996(3) Å for the outer rings. The Cu–O(1) distance is 2.454(3) Å. The central six-membered ring of the tetradentate ligand has a boat conformation, whereas the two terminal six-membered chelate rings of the amine ligand adopt the chair conformation.

Oxorhenium(V) Complexes Derived from 8,17-Dimethyl-6,15-Dioxo- 5,7,14,16-Tetrahydrodibenzo[a,h][14] Annulene-2,11-Dicarboxylic Acid and their Pyrolytical Products

A new series of oxorhenium(V) complexes were prepared by reaction of 8,17-dimethyl-6,15-dioxo-5,7,14,16-tetrahydrodibenzo[a,h][14] annulene-2,11-dicarboxylic acid(H4L), alone or with addition of PPh3 or NaSCN, with H2[ReOCl5]. Mononuclear complexes, [ReO(H4L)Cl]Cl2, [ReO(H4L)(PPh3)]Cl3, and [ReO(H4L)- (SCN)]Cl2 were obtained in 6 N HCl, while the binuclear complex, [Re2O3(H4L)2]Cl4 was obtained in 2 N HCl. Thermal studies on these complexes showed the possibility of obtaining new complexes pyrolytically, where the complexes decompose through several isolable as well as nonisolable, intermediates during heating. [Re2O3(H2L)2], [ReO(H2L)Cl], [ReO(H2L)(PPh3)]Cl, and [ReO(H2L)(SCN)], were synthesized pyrolytically in the solid state from the respective precursor rhenium complexes. All of the prepared complexes and their thermal products have octahedral configurations. The ligand (H4L) behaves either as a neutral tetradentate or dianionic tetradentate ligand towards the oxorhenium ions in these complexes. The carboxylate groups are not coordinated to oxorhenium ions, which was checked by the acidity test and/or addition of metal ions such as Cu(II) and Ni(II), where a variety of new complexes coordinated via carboxylate groups were obtained. The screening of antibacterial and antifungal activities on the free ligand and all complexes, showed higher antifungal activities against Alternaria alternata than against Aspergillus fumigatus. The structures of all complexes and the corresponding thermal products were elucidated by elemental analyses, conductance, IR and electronic absorption spectra, magnetic moments, 1H-NMR and TG-DSC measurements as well as by mass spectrometry.

CHROMIUM(III) COMPLEXES OF 1,2-DI(IMINO-4′-ANTI PYRINYL)ETHANE

ABSTRACT Chromium(III) complexes of the Schiff base 1,2-di(imino-4′-antipyrinyl)ethane (GA) have been synthesized and characterized by elemental analyses, electrical conductance in non-aqueous solvents, infrared and electronic spectra as well as magnetic susceptibility measurements. The complexes have the general formulae [Cr(GA)(ClO4)](ClO4)2 and [Cr(GA)-X2]X (X=NO3, Cl or Br). In the complexes, GA acts as a neutral tetradentate ligand coordinating through both carbonyl oxygens and both azomethine nitrogens. In the perchlorate complex one of the anions is coordinated in a bidentate fashion while in the corresponding nitrate and halide complexes two of the anions are coordinated to the metal ion. A distorted octahedral geometry is assigned around the Cr(III) ion in all of these complexes.

Synthesis and Pyrolytical Studies of New Oxorhenium(V) Complexes with a Tetraaza Macrocyclic Ligand

5,12-dioxa-7,14-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,8-diene (N4L) reacts with the starting oxorhenium(V) complex, H2[ReOCl5], to yield either mononuclear [ReO(N4L)(OH2)]Cl3, or dinuclear [Re2O3(N4L)2]Cl4·2H2O depending on the concentration of hydrochloric acid in rhenium complex. The reaction of (N4L) mixed with KSCN or PPh3 with the oxorhenium(V) complex in 6N HCl, yielded the mononuclear complexes [ReO(N4L)(SCN)]Cl2·H2O and [ReO(N4L)(PPh3)]Cl3·H2O respectively. Both complexes have an octahedral configuration. These complexes decompose through several isolable, as well as non-isolable, intermediates during heating. [Re2O3(N4L\\)2] (N4L\\ = dianionic tetradentate ions), [ReO(N4L)Cl]Cl2 and [ReO(N4L\\)(SCN)], were synthesized pyrolytically in the solid state from the corresponding rhenium(V) complexes. All have octahedral configurations. The ligand (N4L) behaves in these complexes either as a neutral tetradentate or dianionic tetradentate ligand towards the oxorhenium ions. All complexes and the corresponding thermal products were isolated and their structures were elucidated by elemental analyses, conductance, IR and electronic absorption spectra, magnetic moments, 1H NMR and TG-DSC measurements as well as by mass spectroscopy.

IRON(III) COMPLEXES OF 1,2-DI(IMINO-4′-ANTIPYRINYL)ETHANE

Iron(III) complexes of the Schiff base 1,2-di(imino-4′-antipyrinyl)ethane (L) have been prepared and characterized by elemental analyses, electrical conductance in non-aqueous solvents, infrared and electronic spectra as well as magnetic susceptibility measurements. The complexes have the general formula [Fe(L)(ClO4)](ClO4)2 and [Fe(L)X2]X (X = NO3, SCN, Cl or Br). L acts as a neutral tetradentate ligand coordinating through both carbonyl oxygens and both azomethine nitrogens. In the perchlorate complex, one of the perchlorate ions is coordinated bidentately while in the nitrate and thiocyanate complexes two of the anions are coordinated monodentately to the metal ion. In the chloride and bromide complexes, two of the halide ions are coordinated. A high-spin octahedral geometry is assigned around Fe(III) in all of these complexes.

MANGANESE(II) COMPLEXES OF 1,2-DI(IMINO-4′-ANTIPYRINYL)ETHANE

Manganese(II) complexes of the Schiff base 1,2-di(imino-4′-antipyrinyl)-ethane (GA) have been synthesized and characterized by elemental analyses, electrical conductance in non-aqueous solvents, infrared and electronic spectra as well as magnetic susceptibility measurements. The complexes have the general formulae [Mn(GA)X2] (X = ClO4, NO3, Cl, Br or I). GA acts as a neutral tetradentate ligand coordinating through both carbonyl oxygens and both azomethine nitrogens. Both anions are coordinated to the metal ion and the perchlorate as well as nitrate ions are monodentate. A high-spin octahedral geometry is assigned around Mn(II) in all of these complexes.

COPPER(II) COMPLEXES OF 1,2-DI(IMINO-4′-ANTIPYRINYL)ETHANE AND 4-N-(4′-ANTIPYRYLMETHYLIDENE)AMINOANTIPYRINE

Copper(II) complexes of the Schiff bases 1,2-di(imino-4′-antipyrinyl)ethane (GA) and 4-N-(4′-antipyrylmethylidene)aminoantipyrine (AA) have been synthesized and characterized by elemental analyses, electrical conductance in non-aqueous solvents, infrared, electronic and EPR spectra as well as magnetic susceptibility measurements. The complexes have the general formulae [Cu(GA)]X2 (where X = ClO4 or NO3), [Cu(GA)X2] (where X = Cl or Br), [Cu(AA)2]X2 (where X = ClO4, NO3 or Cl) and [Cu(AA)Br]Br. GA acts as a neutral tetradentate ligand coordinating through both carbonyl oxygens and both azomethine nitrogens. In the perchlorate and nitrate complexes of GA, both anions remain ionic while in the corresponding halide complexes both anions are coordinated to the metal ion. AA acts as a neutral bidentate ligand coordinating through one of the carbonyl oxygens and the azomethine nitrogen in the perchlorate, nitrate and chloride complexes, while the coordination of AA occurs in a neutral tridentate fashion through both carbonyl oxygens and the azomethine nitrogen in the bromide complex. In the perchlorate, nitrate and chloride complexes of AA both anions remain ionic, while in the bromide complex, one of the bromides is coordinated to the metal ion. A square-planar geometry is assigned around the Cu(II) ion in all these complexes except the chloride and bromide complexes of GA, which are of distorted-octahedral geometry.

Complexes of Nickel(II) with 1,2-DI(imino-47′-antipyrinyl)Ethane and 4-N-(4′-antipyrylmethylidene)aminoantipyrine

Nickel(II) complexes of the Schiff bases 1,2-di(imino-4′-antipyrinyl)ethane (GA) and 4-N-(4′-antipyrylmethylidene)aminoantipyrine (AA) having the compositions [Ni(GA)]X2 and [Ni(AA)2]X2 (where X - ClO4, NO3, Cl, Br or I) have been prepared and characterized by elemental analyses, electrical conductance in non-aqueous solvents, infrared and electronic spectra as well as magnetic susceptibility measurements. GA acts as a neutral tetradentate ligand coordinating through both carbonyl oxygens and both azomethine nitrogens while AA acts as a neutral bidentate ligand coordinating through one of the carbonyl oxygens and the azomethine nitrogen. In all these complexes both the anions are not coordinated resulting in a square planar geometry around the Ni(II) ion in complexes of GA and a tetrahedral geometry in complexes of AA.

Cobalt(II) complexes of 1,2-(diimino-4′-antipyrinyl)ethane and 4-N-(4′-antipyrylmethylidene)aminoantipyrine

Cobalt(II) complexes of the Schiff bases 1,2-(diimino-4′-antipyrinyl)ethane (GA) and 4-N-(4′-antipyrylmethylidene)aminoantipyrine (AA) have been prepared and characterised by elemental analysis, electrical conductance in non-aqueous solvents, i.r. and electronic spectra, as well as by magnetic susceptibility measurements. The complexes have the general formulae [Co(GA)X]X (X = ClO−4 or NO3−), [Co(GA)X2] (X = Cl−, Br− or I−), [Co(AA)2]X2 (X = ClO4−, NO3−, Br− or I−) and [Co(AA)Cl2]. GA acts as a neutral tetradentate ligand, coordinating through both carbonyl oxygens and both azomethine nitrogens. In the perchlorate and nitrate complexes of GA one anion is coordinated in a bidentate fashion, whereas in the halide complexes both anions are coordinated to the metal, generating an octahedral geometry around the Co ion. AA acts as a neutral bidentate ligand, coordinating through the carbonyl oxygen derived from the aldehydic moiety and the azomethine nitrogen. Both anions remain ionic in the perchlorate, nitrate, bromide and iodide complexes of AA, whereas both anions are coordinated to the metal ion in the chloride complex, resulting tetrahedral geometry around the Co ion.

Metal Complexes of New, Chiral N(2)O(2) Tetradentate Ligands.

N,N'-Bis(2R-hydroxy-2R-phenylethyl)-N,N'-dimethyl-1R,2R-diaminocyclohexane, H(2)L1, and N,N'-bis(2S-hydroxy-2S-methylethyl)-N,N'-dimethyl-1R,2R-diaminocyclohexane, H(2)L2, have been synthesized from readily available chiral precursors. They coordinate as neutral tetradentate ligands to Ni(II) and Cu(II) ions, from which the thiocyanates [M(H(2)L)(NCS)(2)] have been isolated and the structures of the H(2)L1 complexes determined by single-crystal X-ray techniques. In the blue complex [Ni(H(2)L1)(NCS)(2)].H(2)O.2EtOH, 1, and green [Cu(H(2)L1)(NCS)(2)]. 0.5H(2)O, 2, the neutral tetradentate ligands coordinate with the cis-alpha geometry with mutually cis N-bound thiocyanate groups, though the chiral ligands adopt a different stereochemistry in the two complexes. In 2, the absolute configuration about the Cu(II) center is Delta, with the nitrogens possessing the S stereochemistry, whereas for the Ni(II) analogue, coordination gives the Lambda isomer with the R configuration at the stereogenic nitrogens. Addition of H(2)L1 or H(2)L2 to Mn(II) in basic methanol solution results in rapid aerial oxidation. Delta-cis-alpha-[Mn(L1)(OMe)(2)].MeOH, 3, was isolated as black crystals from the reaction mixture after addition of 2 mol of NaOMe. The analogous complex with (L2)(2)(-) proved extremely hygroscopic and was not obtained in pure form. Colorless crystals of Lambda-cis-alpha-[MoO(2)(L1)], 4, were precipitated from a methanolic solution of [MoO(2)(acac)(2)] and H(2)L1. The analogous reaction with H(2)L2 gave Delta-cis-alpha-[MoO(2)(L2)], 5. Structures of 3, 4, and 5 are reported. The reactions of H(2)L1 and H(2)L2 with 1 mol equiv of [Ti(OPr(i))(4)] produced the complexes Delta-cis-alpha-[Ti(L1)(OPr(i))(2)] (white solid) and Lambda-cis-alpha-[Ti(L2)(OPr(i))(2)] (colorless oil), structural assignments for which were made possible by analysis of their (1)H NOE difference spectra. Thus the coordination of these tetradentate ligands is stereospecific, but the absolute configuration of the complexes formed (Delta or Lambda) is dependent on the metal ion involved.

Synthesis and physicochemical studies of yttrium and lanthanide nitrate complexes of 1,2-(diimino-4′-antipyrinyl)ethane

Yttrium and lanthanide nitrate complexes of the Schiff base, 1,2-(diimino-4′-antipyrinyl)ethane (GA), of the type [Ln(GA)2(NO3)3] (where Ln=Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho or Er) have been synthesised and characterised by elemental analyses, electrical conductance, magnetic susceptibility, infrared, proton NMR and electronic spectra, and thermogravimetric studies. Infrared and proton NMR spectra of these complexes show that GA acts as a neutral tetradentate ligand and that all the three nitrate groups are coordinated monodentately. The electronic spectra of the Pr, Nd, Ho and Er complexes suggest reasonable covalency in the metal-ligand bond. The magnetic moments of these complexes are in agreement with the van Vleck values. All these complexes are thermally stable up to about 200°C. A coordination number of eleven may be assigned to the metal ions in these complexes.

Synthesis and Characterisation of Iodide Complexes of Yttrium and Lanthanides With 1, 2-(Diimino-4′-Antipyrinyl) Ethane

Abstract Ten novel complexes of the iodides of yttrium and lanthanides with the Schiff base 1,2-(diimino-4′-antipyrinyl)ethane (GA) having the general formula [Ln(GA)2I]I2, where Ln = Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho and Er have been synthesised and characterised by elemental analyses, molar conductance in non-aqueous solvents, infrared, proton NMR (M = Y and La) and electronic spectra (in the solid and liquid state), magnetic moments and thermogravimetric analysis. The Schiff base GA acts as a neutral tetradentate ligand, coordinating through both carbonyl oxygens and both azomethine nitrogens. One of the iodides is coordinated to the metal ion. A coordination number of nine may be assigned to the metal ion in these complexes.

Studies on Some Bivalent Metal Complexes of Schiff Bases

Abstract 2-Acetylfuran-2-furoylhydrazone (Haffh), 2-acetylthiophene-2-furoylhydrazone (Hatfh), o-hydroxyacetophenone-2-furoylhydrazone (H2hafh) and 2,6-diacetyl pyridine bis(2-furoylhydrazone) (H2dapfh) react with zinc(II), cadmium(II) and mercury(II) chlorides and form the complexes of the types ML2Cl2 [M = Cd(II) and Hg(II), L = Haffh and Hatfh; M = Zn(II), Cd(II) and Hg(II), L = H2hafh], [MLCl]Cl [M = Cd(II) and Hg(II) and L = H2dapfh] and Zn(Hhafh)2. The complexes M(H2acacfh)Cl2 [M = Cd(II) and Hg(II), H2acacfh = acetylacetonebis(2-furoylhydrazone)] were prepared by template reaction. The complexes were characterized by elemental analyses and molar conductance. Infrared spectral studies reveal neutral bidentate bonding of Haffh, Hatfh and H2hafh in the complexes, except Zn(Hhafh)2, in which the Schiff base is bonded in an uninegative tridentate fashion. H2dapfh is a neutral pentadentate ligand while H2acacfh is neutral tetradentate ligand. These observations are also supported by 1H and 13C n.m.r. spe...

Facile synthesis of substituted nitrilotriacetamides

Ligands which contain multiple amide groups represent interesting possibilities as chelating agents. We report here a facile synthesis and crystal structure of nitrilotriacetamide, 2, a neutral tetradentate ligand which we have been studying for metal complexation. Also described herein is a divergent synthesis of the mono-, di- and trimethylated and dimethyl-monoalkyl derivatives of 2.