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.     

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 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.     

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.     

Mixed ligand complexes involved in the system pyridoxamine-glycylglycine-imidazole copper(II)

Ternary as well as quaternary complexes involved in the system pyridoxamine-glycylglycine-imidazole-copper(II) have been studied by pH-metric titration at 37°C and I = 0.15 M (NaNO₃). The data were assessed by program MINIQUAD 75. The formation constants were compared with those obtained from the system of pyridoxamine-glycine-imidazole with some bivalent metal ions previously reported. They are ～ 2.5 log units less. In addition, the enhancement of quaternary complex formation has been described in terms of binary and ternary complex formation reactions. It has been also found that deprotonation of the peptidic proton of glycylglycine took place in the presence of more than one different ligand.     

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.     

Syntheses,equilibrium, and structural studies of copper(II) and nickel(II) complexes with a tripodal alanine-based ligand

A heptadentate ligand, tris[(L)-alanyl-2-carboxamidoethyl]amine (H₃trenala), has been synthesized as its tetrahydrochloride salt; its protonation constants and the stability constants of the copper(II) and nickel(II) chelates have been determined by potentiometry. Mononuclear species with protonated, neutral, or deprotonated forms of the ligand, [Cu(H₅trenala)]⁴⁺, [M(H₄trenala)]³⁺, [M(H₃trenala)]²⁺, [M(H₂trenala)]⁺, and [M(Htrenala)] (M?=?Cu²⁺ and Ni²⁺) have been detected in all cases, while only Cu²⁺ gives dinuclear [Cu₂(H₂trenala)]²⁺, [Cu₂(Htrenala)]²⁺, [Cu₂(trenala)]⁺, and [Cu₂(trenala)(OH)] species. Two dinuclear copper(II) complexes have been prepared and characterized by spectroscopic techniques (IR, UV-Vis, mass electro-spray) and thermogravimetric analysis.     

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)).     

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.     

Preparation and characterization of mononuclear nickel(II) and copper(II) complexes of a hexaazamacrobicyclic ligand

Summary The structure of the hexaazamacrobicycle, sarcophagine, (diAMMEsar)·2H₂O, formed by extracting Co ion from the [Co(diAMMEsar H₂)]Cl₅·-H₂O cage with 8-hydroxyquinoline, has been determined by elemental analysis, and i.r., u.v.-vis., ¹H-n.m.r. and mass spectroscopies. Two octahedral complexes, [M(diAMM-EsarH₂)]Cl₄·2H₂O (M = Ni^II or Cu^II), have been prepared and characterized. The e.s.r. spectrum of the Cu^II complex in the solid state indicates spin-exchange interaction between the Cu^II ions. However, in CD₃OD-D₂O (10%) at 77K, the spectrum is characteristic of a compound having axial symmetry (d _x ²−y ²).     

Trigonal-bipyramidal tin(IV) complexes containing tetradentate tripodal tristhiolatophosphine ligands: synthesis, characterization, crystal structure, and transmetalation reactions

The reactions of the lithium salts of the proligands P(C(6)H(4)-2-SH)(3) (P((H)SH)(3)), P(C(6)H(3)-3-SiMe(3)-2-SH)(3) (P((TMS)SH)(3)), and P(C(6)H(3)-5-Me-2-SH)(3) (P((Me)SH)(3)) with RSnCl(3) (R = Ph, Me, n-Bu), in THF at 0 degrees C, produced a series of trigonal-bipyramidal complexes of the type RSn(PS(3)). The crystal structures of PhSn(P(H)S(3)), PhSn(P(TMS)S(3)), and PhSn(P(Me)S(3)) reveal considerable distortion from local C(3v) symmetry for the Sn(PS(3)) group. Unique to PhSn(P(Me)S(3)) is the presence of intramolecular hydrogen bonding between one sulfur atom and an ortho H atom of the Ph group, creating a plane that includes this S atom and the corresponding C(6)H(3) ring, a phosphorus atom, and the PhSn group. An analysis of the (1)H, (13)C, and (31)P NMR data from a combination of HMQC, HMBC, 2-D COSY, and (1)H{(31)P} NMR studies reveals that in solution the Sn(PS(3)) groups exhibit local C(3v) symmetry, even at low temperature. Byproducts frequently found in the synthesis of the proligands and tin complexes, and subsequent reactions, result from the oxidation of the trianionic tristhiolatophosphine ligand. The crystal structure of one of these, [OP((H)S(3))](2), shows that the molecule contains two ligands joined by a S-S bond. Within each original ligand the remaining two sulfur atoms form a S-S bond, and each phosphorus atom is oxidized. PhSn(P(TMS)S(3)) reacted with 2 equiv of FeCl(3) in CH(2)Cl(2) to produce the iron(IV) complex FeCl(P(TMS)S(3)). FeCl(P(TMS)S(3)) decomposed in the presence of excess FeCl(3). Similar transmetalation reactions with FeCl(2) or [Fe(2)OCl(6)](2)(-) required the addition of ferrocenium ion to complete the oxidation of iron to 4+. RuCl(P(TMS)S(3)) was prepared by the reaction between PhSn(P(TMS)S(3)) and RuCl(2)(DMSO)(4) without the addition of an external oxidizing agent.     

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.     

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.     

Structural comparison of copper(I) and copper(II) complexes with tris(2-pyridylmethyl)amine ligand

Copper(I) complexes with the tris(2-pyridylmethyl)amine (TPMA) ligand were synthesized and characterized to examine the effect of counteranions (Br(-), ClO(4)(-), and BPh(4)(-)), as well as auxiliary ligands (CH(3)CN, 4,4'-dipyridyl, and PPh(3)) on the molecular structures in both solid state and solution. Partial dissociation of one of the pyridyl arms in TPMA was not observed when small auxiliary ligands such as CH(3)CN or Br(-) were coordinated to copper(I), but was found to occur with larger ones such as PPh(3) or 4,4'-dipyridyl. All complexes were found to adopt a distorted tetrahedral geometry, with the exception of [Cu(I)(TPMA)][BPh(4)], which was found to be trigonal pyramidal because of stabilization via a long cuprophilic interaction with a bond length of 2.8323(12) ?. Copper(II) complexes with the general formula [Cu(II)(TPMA)X][Y] (X = Cl(-), Br(-) and Y = ClO(4)(-), BPh(4)(-)) were also synthesized to examine the effect of different counterions on the geometry of [Cu(II)(TPMA)X](+) cation, and were found to be isostructural with previously reported [Cu(II)(TPMA)X][X] (X = Cl(-) or Br(-)) complexes.     

Monomeric and dimeric copper(II) complexes of a novel tripodal peptide ligand: structures stabilized via hydrogen bonding or ligand sharing

The novel tripodal ligand N-(bis(2-pyridyl)methyl)-2-pyridinecarboxamide (Py3AH) affords monomeric and dimeric copper(II) complexes with coordinated carboxamido nitrogens. Although many chloro-bridged dimeric copper(II) complexes are known, [Cu(Py3A)(Cl)] (1) remains monomeric and planar with a pendant pyridine and does not form either a chloro-bridged dimer or the ligand-shared dimeric complex [Cu(Py3A)(Cl)]2 (4) in solvents such as CH3CN. When 1 is dissolved in alcohols, square pyramidal alcohol adducts [Cu(Py3A)(Cl)(CH3OH)] (2) and [Cu(Py3A)(Cl)(C2H5OH)] (3) are readily formed. In 2 and 3, the ROH molecules are bound at axial site of copper(II) and the weak axial binding of the ROH molecule is strengthened by intramolecular hydrogen bonding between ROH and the pendant pyridine nitrogen. Two ligand-shared dimeric species [Cu(Py3A)(Cl)]2 (4) and [Cu(Py3A)]2(ClO4)2 (5) have also been synthesized in which the pendant pyridine of one [Cu(Py3A)] unit completes the coordination sphere of the other [Cu(Py3A)] neighbor. These ligand-shared dimers are obtained in aqueous solutions or in complete absence of chloride in the reaction mixtures.     

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.     

Novel polymers from atom transfer polymerisation mediated by copper(I) Schiff base complexes

The use of copper(I) Schiff base complex catalysed atom transfer polymerisation of methacrylates is described. The use of a range of functional and multi‐functional initiators enables the synthesis of a range of functional and star polymers to be prepared under undemanding synthetic conditions. End capping with silyl enol ethers allows for ω‐functional polymers. The combination of novel initiators, functional monomers and end capping allows an unprecedented array of macromolecular structures to be produced with limited need for protecting group chemistry.     

Synthesis and characterization of cobalt(II) complexes with tripodal polypyridine ligand bearing pivalamide groups. Selective formation of six- and seven-coordinate cobalt(II) complexes

The reactions of CoX(2) (X = Cl(-), Br(-), I(-) and ClO(4)(-)) with the tripodal polypyridine N(4)O(2)-type ligand bearing pivalamide groups, bis(6-(pivalamide-2-pyridyl)methyl)(2-pyridylmethyl)amine ligand (H(2)BPPA), afforded two types of Co(II) complexes as follows. One type is purple-coloured Co(II) complexes, [CoCl(2)(H(2)BPPA)] (1(Cl)) and [CoBr(2)(H(2)BPPA)] (1(Br)) which were prepared when X = Cl(-) and Br(-), respectively. The other type is pale pink-coloured Co(II) complexes, [Co(MeOH)(H(2)BPPA)](ClO(4)(-))(2) (2·(ClO(4)(-))(2)) and [Co(MeCN)(H(2)BPPA)](I(-))(2) (2·(I(-))(2)), which were obtained when X = I(-) and ClO(4)(-), respectively. From the reaction of 1(Cl) and NaN(3), a purple-coloured complex, [Co(N(3))(2)(H(2)BPPA)] (1(azide)), was obtained. These Co(II) complexes were characterized by X-ray structural analysis, IR and reflectance spectroscopies, and magnetic susceptibility measurements. All these Co(II) complexes were shown to be in a d(7) high-spin state based on magnetic susceptibility measurements. The former Co(II) complexes revealed a six-coordinate octahedron with one amine nitrogen, three pyridyl nitrogens, and two counter anions, and one coordinated anion, Cl(-), Br(-) and N(3)(-), forming intramolecular hydrogen bonds with two pivalamide N-H groups. On the other hand, the latter Co(II) complexes showed a seven-coordinate face-capped octahedron with one amine nitrogen, three pyridyl nitrogens, two pivalamide carbonyl oxygens and MeCN or MeOH. In these structures, intramolecular hydrogen bonding interaction was not observed, and the metal ion was coordinated by the pivalamide carbonyl oxygens and solvent molecule instead of the counter anions. The difference in coordination geometries might be attributable to the coordination ability and ionic radii of the counteranions; smaller strongly binding anions such as Cl(-), Br(-) and N(3)(-) gave the former complexes, whereas bulky weakly binding anions such as I(-) and ClO(4)(-) afforded the latter ones. In order to demonstrate this hypothesis, the small stronger coordinating ligand, azide, was added to complexes 2·(ClO(4)(-))(2) to obtain the dinuclear cobalt(II) complex in which two six-coordinate octahedral cobalt(II) species were bridged with azide, 3·(ClO(4)(-)). Also, the abstraction reaction of halogen anions from complexes 1(Cl) by AgSbF(6) gave a pale pink Co(II) complex assignable to 2·(SbF(6)(-))(2).     

Synthesis of an asymmetrical tripodal tetraamine ligand and its five-coordinate copper(II) complex

A simple synthesis has been devised for the tripodal 3,3,4-tetraamine ligand N{(CH2)3NH2}2{(CH2)4NH2} (L). This ligand forms a copper(II) complex, [Cu (LH)Cl2]ClO4 (7), the structure of which has been determined by X-ray diffraction. The cation contains a five-coordinate copper atom, bonded to two chloride ions, the two propylamine groups and the tertiary nitrogen atom of the ligand; the arrangement is a distorted trigonal bipyramid, in which the two primary amine groups occupy the axial positions. The butylamine group of the ligand does not coordinate to copper but is protonated. It is involved in hydrogen bonding to the perchlorate ion. The e.p.r. spectrum of [Cu(dpt)Cl2] is very similar to that of (7), suggesting that it also has a trigonal bipyramidal structure. This revised version was published online in June 2006 with corrections to the Cover Date.