Four copper(II) complexes with potentially tetradentate tripodal ligands

The four title Cu^II compounds are chloro­[(2‐furyl­methyl)­bis(2‐pyridyl­methyl)­amine‐N,N′,N′′]copper(II) perchlorate, [CuCl(C₁₇H₁₇N₃O)]ClO₄, (I), chloro{2‐[bis(2‐pyridyl­methyl)­amino]­ethano­lato‐N,N′,N′′,O}­copper(II) hemi­[tetra­chloro­copper(II)], [CuCl(C₁₄H₁₇N₃O)][CuCl₄]_1/2, (II), chloro­[(2‐morpholino­ethyl)­bis(2‐pyridyl­methyl)­amine‐N,N′,N′′,N′′′]copper(II) perchlorate, [CuCl(C₁₈H₂₄N₄O)]ClO₄, (III), and chloro­[(2‐piperidinyl­ethyl)­bis(2‐pyridyl­methyl)­amine‐N,N′,N′′,N′′′]­copper(II) hexa­fluoro­phosphate, [CuCl(C₁₉H₂₆N₄)]­PF₆, (IV). They have tripodal potentially tetradentate ligands. In (I), the O atom of the furan moiety weakly coordinates to the Cu atom at a distance of 2.750 (3) Å.     

Synthesis, characterization, and structures of copper(II)-thiosulfate complexes incorporating tripodal tetraamine ligands

The reaction of [Cu(L)(H(2)O)](2+) with an excess of thiosulfate in aqueous solution produces a blue to green color change indicative of thiosulfate coordination to Cu(II) [L = tren, Bz(3)tren, Me(6)tren, and Me(3)tren; tren = tris(2-aminoethyl)amine, Bz(3)tren = tris(2-benzylaminoethyl)amine, Me(6)tren = tris(2,2-dimethylaminoethyl)amine, and Me(3)tren = tris(2-methylaminoethyl)amine]. In excess thiosulfate, only [Cu(Me(6)tren)(H(2)O)](2+) promotes the oxidation of thiosulfate to polythionates. Products suitable for single-crystal X-ray diffraction analyses were obtained for three thiosulfate complexes, namely, [Cu(tren)(S(2)O(3))].H(2)O, [Cu(Bz(3)tren)(S(2)O(3))].MeOH, and (H(3)Me(3)tren)[Cu(Me(3)tren)(S(2)O(3))](2)(ClO(4))(3). Isolation of [Cu(Me(6)tren)(S(2)O(3))] was prevented by its reactivity. In each complex, the copper(II) center is found in a trigonal bipyramidal (TBP) geometry consisting of four amine nitrogen atoms, with the bridgehead nitrogen in an axial position and an S-bound thiosulfate in the other axial site. Each structure exhibits H bonding (involving the amine ligand, thiosulfate, and solvent molecule, if present), forming either 2D sheets or 1D chains. The structure of [Cu(Me(3)tren)(MeCN)](ClO(4))(2) was also determined for comparison since no structures of mononuclear Cu(II)-Me(3)tren complexes have been reported. The thiosulfate binding constant was determined spectrophotometrically for each Cu(II)-amine complex. Three complexes yielded the highest values reported to date [K(f) = (1.82 +/- 0.09) x 10(3) M(-1) for tren, (4.30 +/- 0.21) x 10(4) M(-1) for Bz(3)tren, and (2.13 +/- 0.05) x 10(3) M(-1) for Me(3)tren], while for Me(6)tren, the binding constant was much smaller (40 +/- 10 M(-1)).     

Synthesis and characterization of picolinate-containing nickel(II) complexes with tridentate and tripodal tetradentate ligands

Two picolinate-containing nickel(II) complexes [Ni(bbma)(pic)(H₂O)]ClO₄ · CH₃OH (1) and [Ni(ntb)(pic)]Cl · CH₃OH · 3H₂O (2) were synthesized and characterized by infrared, elemental analysis, UV-Vis, and X-ray diffraction analyses, where bbma is bis(benzimidazol-2-yl-methyl)amine, ntb is tris(2-benzimidazolylmethyl)amine, pic is the anion of picolinic acid. X-ray analysis shows that both complexes are mononuclear with picolinate coordinated to Ni(II) in a μ₂-N,O chelating mode. Both complexes adopt distorted octahedral geometry. Intermolecular N–H ··· O and O–H ··· O hydrogen bonds and π–π interactions in 1 and 2 are important in stabilization of the crystal structures.     

Nickel(II) and copper(II) complexes of unsymmetrical tetradentate reduced Schiff base ligands

Two new reduced Schiff base ligands, [HL¹ = 4-{2-[(pyridin-2-ylmethyl)-amino]-ethylimino}-pentan-2-one and HL² = 4-[2-(1-pyridin-2-yl-ethylamino)-ethylimino]-pentan-2-one] have been prepared by reduction of the corresponding tetradentate unsymmetrical Schiff bases derived from 1:1: 1 condensation of 1,2-ethanediamine, acetylacetone and pyridine-2-carboxaldehyde/2-acetyl pyridine. Four complexes, [Ni(L¹)]ClO₄ (1), [Cu(L¹)]ClO₄ (2), [Ni(L²)]ClO₄ (3), and [Cu(L²)]ClO₄ (4) with these two reduced Schiff base ligands have been synthesized and structurally characterized by X-ray crystallography. The mono-negative ligands L¹ and L² are chelated in all four complexes through the four donor atoms to form square planar nickel(II) and copper(II) complexes. Structures of 3 and 4 reveal that enantiomeric pairs are crystallized together with opposite chirality in the nitrogen and carbon atoms. The two Cu^II complexes (2 and 4) exhibit both irreversible reductive (Cu^II/Cu^I; E_pc, −1.00 and −1.04 V) and oxidative (Cu^II/Cu^III; E_pa, +1.22 and +1.17 V, respectively) responses in cyclic voltammetry. The electrochemically generated Cu^I species for both the complexes are unstable and undergo disproportionation.     

Non-heme iron(II) complexes containing tripodal tetradentate nitrogen ligands and their application in alkane oxidation catalysis

A series of iron(II) bis(triflate) complexes containing tripodal tetradentate nitrogen ligands with pyridine and dimethylamine donors of the type [N(CH(2)Pyr)(3-n)()(CH(2)CH(2)NMe(2))(n)] [n = 0 (tpa, 1), n = 1 (iso-bpmen, 3), n = 2 (Me(4)-benpa, 4), n = 3 (Me(6)-tren, 5)] and the linear tetradentate ligand [(CH(2)Pyr)MeN(CH(2)CH(2))NMe(CH(2)Pyr), (bpmen, 2)] has been prepared. The preferred coordination geometry of these complexes in the solid state and in CH(2)Cl(2) solution changes from six- to five-coordinate in the order from 1 to 5. In acetonitrile, the triflate ligands of all complexes are readily displaced by acetonitrile ligands. The complex [Fe(1)(CH(3)CN)(2)](2+) is essentially low spin at room temperature, whereas ligands with fewer pyridine donors increase the preference for high-spin Fe(II). Both the number of pyridine donors and the spin state of the metal center strongly affect the intensity of a characteristic MLCT band around 400 nm. The catalytic properties of the complexes for the oxidation of alkanes have been evaluated, using cyclohexane as the substrate. Complexes containing ligands 1-3 are more active and selective catalysts, possibly operating via a metal-based oxidation mechanism, whereas complexes containing ligands 4 and 5 give rise to Fenton-type chemistry.     

Copper(I) complexes, copper(I)/O(2) reactivity, and copper(II) complex adducts, with a series of tetradentate tripyridylalkylamine tripodal ligands

Copper(I) and copper(II) complexes possessing a series of related ligands with pyridyl-containing donors have been investigated. The ligands are tris(2-pyridylmethyl)amine (tmpa), bis[(2-pyridyl)methyl]-2-(2-pyridyl)ethylamine (pmea), bis[2-(2-pyridyl)ethyl]-(2-pyridyl)methylamine (pmap), and tris[2-(2-pyridyl)ethyl]amine (tepa). The crystal structures of the protonated ligand H(tepa)ClO(4), the copper(I) complexes [Cu(pmea)]PF(6) (1b-PF(6)), [Cu(pmap)]PF(6) (1c-PF(6)), and copper(II) complexes [Cu(pmea)Cl]ClO(4).H(2)O (2b-ClO(4).H(2)O), [Cu(pmap)Cl]ClO(4).H(2)O (2c-ClO(4).H(2)O), [Cu(pmap)Cl]ClO(4) (2c-ClO(4)), and [Cu(pmea)F](2)(PF(6))(2) (3b-PF(6)) were determined. Crystal data: H(tepa)ClO(4), formula C(21)H(25)ClN(4)O(4), triclinic space group P1, Z = 2, a = 10.386(2) A, b = 10.723(2) A, c = 11.663(2) A, alpha = 108.77(3) degrees, beta = 113.81(3) degrees, gamma = 90.39(3) degrees; 1b-PF(6), formula C(19)H(20)CuF(6)N(4)P, orthorhombic space group Pbca, Z = 8, a = 14.413(3) A, b = 16.043(3) A, c = 18.288(4) A, alpha = beta = gamma = 90 degrees; (1c-PF(6)), formula C(20)H(22)CuF(6)N(4)P, orthorhombic space group Pbca, Z = 8, a = 13.306(3) A, b = 16.936(3) A, c = 19.163(4) A, alpha = beta = gamma = 90 degrees; 2b-ClO(4).H(2)O, formula C(19)H(22)Cl(2)CuN(4)O(5), triclinic space group P1, Z = 4, a = 11.967(2) A, b = 12.445(3) A, c = 15.668(3) A, alpha = 84.65(3) degrees, beta = 68.57(3) degrees, gamma = 87.33(3) degrees; 2c-ClO(4).H(2)O, formula C(20)H(24)Cl(2)CuN(4)O(5), monoclinic space group P2(1)/c, Z = 4, a = 11.2927(5) A, b = 13.2389(4) A, c = 15.0939(8) A, alpha = gamma = 90 degrees, beta = 97.397(2) degrees; 2c-ClO(4), formula C(20)H(22)Cl(2)CuN(4)O(4), monoclinic space group P2(1)/c, Z = 4, a = 8.7682(4) A, b = 18.4968(10) A, c = 13.2575(8) A, alpha = gamma = 90 degrees, beta = 94.219(4) degrees; 3b-PF(6), formula [C(19)H(20)CuF(7)N(4)P](2), monoclinic space group P2(1)/n, Z = 2, a = 11.620(5) A, b = 12.752(5) A, c = 15.424(6) A, alpha = gamma = 90 degrees, beta = 109.56(3) degrees. The oxidation of the copper(I) complexes with dioxygen was studied. [Cu(tmpa)(CH(3)CN)](+) (1a) reacts with dioxygen to form a dinuclear peroxo complex that is stable at low temperatures. In contrast, only a very labile peroxo complex was observed spectroscopically when 1b was reacted with dioxygen at low temperatures using stopped-flow kinetic techniques. No dioxygen adduct was detected spectroscopically during the oxidation of 1c, and 1d was found to be unreactive toward dioxygen. Reaction of dioxygen with 1a-PF(6), 1b-PF(6), and 1c-PF(6) at ambient temperatures leads to fluoride-bridged dinuclear copper(II) complexes as products. All copper(II) complexes were characterized by UV-vis, EPR, and electrochemical measurements. The results manifest the dramatic effects of ligand variations and particularly chelate ring size on structure and reactivity.     

A facile synthesis of unsymmetrical tetradentate schiff-base ligands and their copper(II) and nickel(II) complexes

A facile synthetic route for unsymmetrical tetradentate Schiff-base ligands has been found by using 5-carboxysalicylaldehyde as a starting material, and their copper(II) and nickel(II) complexes have been prepared and characterized by magnetic susceptibilities, electronic absorption spectra, and polarographic reduction potentials.     

Novel iron(III) complexes of tripodal and linear tetradentate bis(phenolate) ligands: close relevance to intradiol-cleaving catechol dioxygenases

Four new iron(III) complexes of the bis(phenolate) ligands N,N-dimethyl-N',N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine [H2(L1)], N,N-dimethyl-N',N'-bis(2-hydroxy-4-nitrobenzyl)ethylenediamine [H2(L2)], N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine [H2(L3)], and N,N'-dimethyl-N,N'-bis(2-hydroxy-4-nitrobenzyl)ethylenediamine [H2(L4)] have been isolated and studied as structural and functional models for the intradiol-cleaving catechol 1,2-dioxygenases (CTD). The complexes [Fe(L1)Cl] (1), [Fe(L2)(H2O)Cl] (2), [Fe(L3)Cl] (3), and [Fe(L4)(H2O)Cl] (4) have been characterized using absorption spectral and electrochemical techniques. The single-crystal X-ray structures of the ligand H2(L1) and the complexes 1 and 2 have been successfully determined. The tripodal ligand H2(L1) containing a N2O2 donor set represents the metal-binding region of the iron proteins. Complex 1 contains an FeN2O2Cl chromophore with a novel trigonal bipyramidal coordination geometry. While two phenolate oxygens and an amine nitrogen constitute the trigonal plane, the other amine nitrogen and chloride ion are located in the axial positions. In contrast, 2 exhibits a rhombically distorted octahedral coordination geometry for the FeN2O3Cl chromophore. Two phenolate oxygen atoms, an amine nitrogen atom, and a water molecule are located on the corners of a square plane with the axial positions being occupied by the other nitrogen atom and chloride ion. The interaction of the complexes with a few monodentate bases and phenolates and differently substituted catechols have been investigated using absorption spectral and electrochemical methods. The effect of substituents on the phenolate rings on the electronic spectral features and FeIII/FeII redox potentials of the complexes are discussed. The interaction of the complexes with catecholate anions reveals changes in the phenolate to iron(III) charge-transfer band and also the appearance of a low-energy catecholate to iron(III) charge-transfer band similar to catechol dioxygenase-substrate complexes. The redox behavior of the 1:1 adducts of the complexes with 3,5-di-tert-butylcatechol (H2DBC) has been also studied. The reactivities of the present complexes with H2DBC have been studied and illustrated. Interestingly, only 2 and 4 catalyze the intradiol-cleavage of H2DBC, the rate of oxygenation being much faster for 4. Also 2, but not 4, yields an extradiol cleavage product. The reactivity of the complexes could be illustrated not on the basis of the Lewis acidity of the complexes alone but by assuming that the product release is the rate-determining phase of the catalytic reaction.     

Aggregation control by homologous tripodal tetradentate amino acid ligands in oxo-bridged diiron(III) aquo complexes

Isoelectronic oxo-bridged diiron(III) aquo complexes of the homologous tripodal tetradentate amino acid ligands, N,N'-bis(2-pyridylmethyl)-3-aminoacetate (bpg(-)) and N,N'-bis(2-pyridylmethyl)-3-aminopropionate (bpp(-)), containing [(H(2)O)Fe(III)-(mu-O)-Fe(III)(H(2)O)](4+) cores, oligomerise, respectively, by dehydration and deprotonation, or by dehydration only, in reversible reactions. In the solid state, [Fe(2)(O)(bpp)(2)(H(2)O)(2)](ClO(4))(2) (1(ClO(4))(2)) exhibits stereochemistry identical to that of [Fe(2)(O)(bpg)(2)(H(2)O)(2)](ClO(4))(2) (2(ClO(4))(2)), with the ligand carboxylate donor oxygen atoms and the water molecules located cis to the oxo bridge and the tertiary amine group trans to it. Despite their structural similarity, 1(2+) and 2(2+) display markedly different aggregation behaviour in solution. In the absence of significant water, 1(2+) dehydrates and dimerises to give the tetranuclear complex, [Fe(4)(O)(2)(bpp)(4)](ClO(4))(4) (3(ClO(4))(4)), in which the carboxylate groups of the four bpp(-) ligands act as bridging groups between two [Fe(2)(O)(bpp)(2)](2+) units. Under similar conditions, 2(2+) dehydrates and deprotonates to form dinuclear and trinuclear oligomers, [Fe(2)(O)(OH)(bpg)(2)](ClO(4)) (4ClO(4)) and [Fe(3)(O)(2)(OH)(bpg)(3)](ClO(4)) (5(ClO(4))), related by addition of 'Fe(O)(bpg)' units. The trinuclear 5(ClO(4)), characterised crystallographically as two solvates 5(ClO(4)).3H(2)O and 5(ClO(4)).2MeOH, is based on a hexagonal [Fe(3)(O)(2)(OH)(bpg)(3)](+) unit, formally containing one hydroxo and two oxo bridges. The different aggregation behaviour of 1(ClO(4))(2) and 2(ClO(4))(2) results from the difference of one methylene group in the pendant carboxylate arms of the amino acid ligands.     

Syntheses, crystal structures and properties of novel copper(II) complexes obtained by reactions of copper(II) sulfate pentahydrate with tripodal ligands

Three novel metal-organic frameworks (MOFs), [Cu(1)SO4].H2O (4), [Cu2(2)2(SO4)2].4H2O (5) and [Cu(3)(H2O)]SO4.5.5H2O (6), were obtained by hydrothermal reactions of CuSO4.5H2O with the corresponding ligands, which have different flexibility. The structures of the synthesized complexes were determined by single-crystal X-ray diffraction analyses. Complex 4 has a 2D network structure with two types of metallacycles. Complex 5 also has a 2D network structure in which each independent 2D sheet contains two sub-layers bridged by oxygen atoms of the sulfate anions. Complex 6 has a 2D puckered structure in which the sulfate anions serve as counter anions, which are different from those in complexes 4 (terminators) and 5 (bridges). The different structures of complexes 4, 5 and 6 indicate that the nature of organic ligands affected the structures of the assemblies greatly. The magnetic behavior of complex 5 and anion-exchange properties of complex 6 were investigated.     

Identification and characterization of monoanionic tripodal tetradentate ligand complexes of copper(I) and copper(II) involved in halogen atom transfer reactions

The copper(I) complex of bis-(2-(2-pyridyl)-ethyl)-(2-(N-p-toluenesulfonamido)-ethyl)amine (PETAEA), a monoanionic, tripodal tetradentate ligand, was prepared, characterized, and shown to be an effective catalyst for atom transfer radical polymerization (ATRP). A model atom transfer reaction of Cu(PETAEA) with 1-phenylethyl bromide and TEMPO radical trapping agent was studied. The copper(II) complex formed in this reaction was identified by comparison of its spectroscopic data with that of Cu(PETAEA)Br prepared by an independent synthesis. Kinetic and spectroscopic data indicated that the reaction mechanism involved simple atom transfer from the alkyl halide to the Cu(PETAEA) to form the Cu(PETAEA)Br, and no other intermediates were involved. The solid-state structures of the copper(I) and (II) complexes appeared to be maintained in solution, so this system is an atom transfer reaction in which all of the reactive species are identified and characterized.     

Rod-like phases formed by Ni(II) and VO(II) complexes of tetradentate enaminoketone ligands

Most of the nickel(II) complexes of tetradentate enaminoketone ligands obtained, although not strictly calamitic and with a rather low length to width ratio, form enantiotropic rod-like nematic and smectic A phases. Corresponding vanadyl(II) complexes exhibit only monotropic mesophases. The vanadyl complexes, due to their non-planar structure, are chiral with an asymmetry centre placed at the metal ion.     

Stability and acidity constants for ternary ligand-zinc-hydroxo complexes of tetradentate tripodal ligands

Four series of tetradentate tripodal ligands containing pyridyl, 2-imidazolyl, 4-imidazolyl, amino, and/or carboxylic groups were synthesized as hydrolytic zinc enzyme models in order to elucidate the effect of various coordination environments on zinc binding and the acidity of zinc-bound water. In aqueous solution, ligands with same charges showed a good correlation between zinc binding (log K(ZnL)) and zinc-bound water acidity (pK(a) of LZnOH(2)); the stronger the zinc binding, the higher the pK(a). The zinc-bound water acidity decreased as pyridyl groups were replaced by carboxylate groups. However, exchanging amino groups for carboxylate groups gave no change in zinc-bound water acidity regardless of the charge of the atoms in the inner coordination sphere of the metal ion. The results are consistent with the conventional notion that negatively charged carboxylate groups inherently increase zinc binding and result in decreasing zinc-bound water acidity, but also suggest that environmental effects may modulate or dominate control of acidity.     

Synthesis,characterization and comparative studies of mono- and dimeric copper(II) complexes containing tripodal ligands

Mono and dimeric bromo-bridged copper(II) complexes of the type [CuBr₂(L)] and [Cu₂Br₂(L)₂](ClO₄)₂ containing nitrogen donor tripodal ligands L = 2,6-bis(pyrazol-1-yl)pyridine (bppy) or 2,6-bis(3,5-dimethylpyrazol-1-yl)pyridine (dmbppy) have been synthesized. All complexes have been characterized by elemental analysis, IR, ESR and electronic spectra and magnetic susceptibility and cyclic voltammetry measurements.     

Synthesis and characterization of copper(II) complexes incorporating pyrazolyl-derived N,S-donor bidentate ligands

The novel bidentate N,S-donor anionic ligands [PhNCSIndz]^?, [PhNCSImz]^?, [PhNCSPz^Me3]^?, and [EtNCSPz]^?, where Indz?=?indazole, Imz?=?imidazole, Pz^Me3?=?3,4,5-trimethylpyrazole, and Pz?=?pyrazole, were synthesized and used to prepare Cu(II) complexes of general formula [Cu(N^S)₂]. The ligands were synthesized via direct addition of phenylisothiocyanate or ethylisothiocyanate into THF suspensions of the corresponding sodium-pyrazolate salts. All of the synthesized compounds, including the ligands and the complexes, were characterized by physico-chemical and spectroscopic methods, and crystal structures of [Cu(EtNCSPz)₂] and [Cu(PhNCSPz^Me2)₂] were determined by X-ray diffraction analysis, showing a trans-square planar geometry for [Cu(EtNCSPz)₂] and a distorted tetrahedral geometry for [Cu(PhNCSPz^Me2)₂].     

The copper(II) complexes with tetradentate Schiff base ligands: Synthesis, crystal structures, and computational studies

Mononuclear copper(II) Schiff base complexes, Cu(BrSal₂Pn) (I) and Cu(BrSal₂MePn) (II), where BrSal₂Pn = N,N′-bis(5-bromo-2-hydroxybenzylidene)propane-1,3-diamine and BrSal₂MePn = N,N′-bis(5-bromo-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine, have been synthesized and characterized by elemental analyses and single-crystal X-ray diffraction. Also, the optimized geometries of them have been calculated using density functional theory method (B3LYP/6–31g). Obtained structural parameters are in agreement with the experimental data. The geometry around the copper atoms display a distorted square-planner structure by coordinating with two oxygen atoms from the phenols moieties and two nitrogen atoms from the imino groups of ligands and thus established three 6-membered rings.     

Macrocyclic copper(II) and zinc(II) complexes incorporating phosphate esters

Slow evaporation of solutions prepared by adding either Cu(ClO(4))(2).6H(2)O or Zn(ClO(4))(2).6H(2)O to solutions containing appropriate proportions of Me(3)tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) and sodium phenyl phosphate (Na(2)PhOPO(3)) gave dark blue crystals of [Cu(3)(Me(3)tacn)(3)(PhOPO(3))(2)](ClO(4))(2).(1)/(2)H(2)O (1) and colorless crystals of [Zn(2)(Me(3)tacn)(2)(H(2)O)(4)(PhOPO(3))](ClO(4))(2).H(2)O (2), respectively. Blue crystals of [Cu(tacn)(2)](BNPP)(2) (3) formed in an aqueous solution of [Cu(tacn)Cl(2)], bis(p-nitrophenyl phosphate) (BNPP), and HEPES buffer (pH 7.4). Compound 1 crystallizes in the triclinic space group P1 (No. 2) with a = 9.8053(2) A, b = 12.9068(2) A, c = 22.1132(2) A, alpha = 98.636(1) degrees, beta = 99.546(1) degrees, gamma = 101.1733(8) degrees, and Z = 2 and exhibits trinuclear Cu(II) clusters in which square pyramidal metal centers are capped by two phosphate esters located above and below the plane of the metal centers. The trinuclear cluster is asymmetric having Cu...Cu distances of 4.14, 4.55, and 5.04 A. Compound 2 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 13.6248(2) A, b = 11.6002(2) A, c = 25.9681(4) A, beta = 102.0072(9) degrees, and Z = 4 and contains a dinuclear Zn(II) complex formed by linking two units of [Zn(Me(3)tacn)(OH(2))(2)](2+) by a single phosphate ester. Compound 3 crystallizes in the monoclinic space group C2/c (No. 15) with a = 24.7105(5) A, b = 12.8627(3) A, c = 14.0079(3) A, beta = 106.600(1) degrees, and Z = 4 and consists of mononuclear [Cu(tacn)(2)](2+) cations whose charge is balanced by the BNPP(-) anions.     

Electron-transfer kinetics of copper(II/I) tripodal ligand complexes

The electron-transfer kinetics for each of three copper(II/I) tripodal ligand complexes reacting with multiple reducing and oxidizing counter reagents have been examined in aqueous solution at 25 degrees C, mu = 0.10 M. For all of the ligands studied, an amine nitrogen serves as the bridgehead atom. Two of the ligands (PMMEA and PEMEA) contain two thioether sulfurs and one pyridyl nitrogen as donor atoms on the appended legs while the third ligand (BPEMEA) has two pyridyl nitrogens and one thioether sulfur. Very limited kinetic studies were also conducted on two additional closely related tripodal ligand complexes. The results are compared to our previous kinetic study on a Cu(II/I) system involving a tripodal ligand (TMMEA) with thioether sulfur donor atoms on all three legs. In all systems, the Cu(II/I) electron self-exchange rate constants (k(11)) are surprisingly small, ranging approximately 0.03-50 M(-)(1) s(-)(1). The results are consistent with earlier studies reported by Yandell involving the reduction of Cu(II) complexes with four similar tripodal ligand systems, and it is concluded that the dominant reaction pathway involves a metastable Cu(II)L intermediate species (designated as pathway B). Since crystal structures suggest that the ligand reorganization accompanying electron transfer is relatively small compared to our earlier studies on macrocyclic ligand complexes of Cu(II/I), it is unclear why the k(11) values for the tripodal ligand systems are of such small magnitude.     

The gas chromatography of higher substituted tetradentate β-ketoamine copper(II) complexes

The preparation of the Schiff's bases derived from 1,2-diaminoethane and a series of 5-alkyl substituted-1,1,1-trifluoropentan-2:4-diones is described, including the elusive compound obtained from 1,1,1-trifluoro-5,5,5-trimethylpentan-2:4-dione, and trivially denoted as H₂[en(TPM)₂]. Gas chromatography of the copper complexes of these ligands shows increasing retention times as the size of the alkyl substituent is increased, with the exception of Cu[en(TPM)₂] which is unusually volatile and has a much reduced retention time. It is most probable that this graat difference in properties occurs because of the considerable steric hindrance of the tert-butyl groups in the original β-diketone, which prevents the normal condensation reaction with 1,2-diaminoethane taking place. The properties of the metal complexes of H₂[en(TPM)₂] make them ideally suited to quantitative gas chromatography.     

Nickel(II) and copper(II) complexes of macrocyclic and acyclic Schiff-base ligands derived from new asymmetrical tripodal tetraamines and 2,6-diacetylpyridine

The asymmetrical tripodal 4,2,2-tetraamine N{(CH₂)₄NH₂}{(CH₂)₂NH₂}₂ bee, 3,2,2-tetraamine N{(CH₂)₃NH₂} {(CH₂)₂NH₂}₂ pee, and 3,3,2-tetraamine N{(CH₂)₃NH₂}₂{(CH₂)₂NH₂} ppe ligands have been prepared. In the presence of Cu^II or Ni^II ions, these ligands condense with 2,6-diacetylpyridine. In some cases, cyclization occurs and new isomers of CR-type with a pendant primary amine group are formed. In the other cases ring closure does not occur and coordinated acyclic hexadentate ligands have been isolated. At room temperature and in absolute methanol the latter acyclic complexes are usually the only products. I.r., u.v.–vis., reflectance spectra and magnetic moments for the complexes were recorded.