Copper(II) and nickel(II) complexes of binucleating macrocyclic bis(disulfide)tetramine ligands

Novel macrocyclic bis(disulfide)tetramine ligands and several Cu(II) and Ni(II) complexes of them with additional ligands have been synthesized by the oxidative coupling of linear tetradentate N2S2 tetramines with iodine. Facile demetalation of the Ni(II) oxidation products affords the free 20-membered macrocycles meso-9 and rac-9 and the 22-membered macrocycle 16, all of which are potentially octadentate N4S4 ligands. X-ray structure analyses reveal distinctly different conformations for the two isomers of 9; meso-9 shows a stepped conformation in profile with the disulfide groups corresponding to the rise of the step, whereas rac-9 exhibits a V conformation with the disulfide groups near the vertex of the V. No metal complexes of rac-9 have been isolated. Crystallographic studies of three Cu(II) complexes reveal that depending upon the size of the macrocyclic ligand and the nature of the additional ligands (I-, NCO-, and CH3CN), the Cu(II) coordination geometry shows considerable variation (plasticity), with substantial changes in the Cu(II)-disulfide bonding. Thus, a diiodide salt contains six-coordinate Cu(II) to which all four bridging disulfide sulfur atoms form strong equatorial bonds. In contrast, isocyanato complexes of the 20- and 22-membered macrocycles exhibit trigonal-bipyramidal Cu(II) and distorted cis-octahedral Cu(II) geometries, respectively, having only one and no short equatorially bound sulfur atoms. The coordination geometry of the latter complex can also be described as four-coordinate seesaw with two semicoordinated S(disulfide) ligands. Disulfide-->Cu(II) ligand-to-metal charge transfer absorptions of both isocyanato-containing Cu(II) species appear too weak to observe, probably because of poor overlap of the sulfur orbitals with the Cu(II) d-vacancy. The dual disulfide-bridged Ni(II) units of the crystallographically characterized octahedral Ni(II) complex of meso-9 with axial iodide and acetonitrile ligands promote substantial antiferromagnetic coupling (J = -13.0(2) cm-1).     

Structures of Nickel(II) and Copper(II) Complexes of 14-Membered Macrocyclic Quadridentate Ligands

The structures of 41 Ni(II) and 17 Cu(II) complexes of macrocyclic quadridentate ligands have been analyzed, and are discussed about bond lengths, bond angles, conformations, and configurations, upon which many conclusions are formed. The inter- or intra-molecular hydrogen bonds exist among ligands and hydrates in many compounds and play an important role in the structures. There are exhibited two distinct peaks on the histogram of the average Ni-N distances, corresponding to four coordination and six coordination; these average Ni-N distances are 1.95(4) Å and 2.10(5) Å, respectively. The most probable structures of Ni(II) macrocyclic compounds have coordination number six for the metal ion, chair forms for six-membered rings, planar structure for the metal ion and the four donor atoms of the quadridentate ligand and an inversion center at the central metal ion.     

Structural and EPR studies on single-crystal and polycrystalline samples of copper(II) and cobalt(II) complexes with N2S2-based macrocyclic ligands

The properties of Cu(II) and Co(II) complexes with oxygen- or nitrogen-containing macrocycles have been extensively studied; however, less attention has been paid to the study of complexes containing sulfur atoms in the first coordination sphere. Herein we present the interaction between these two metal ions and two macrocyclic ligands with N2S2 donor sets. Cu(II) and Co(II) complexes with the pyridine-containing 14-membered macrocycles 3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L) and 7-(9-anthracenylmethyl)-3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L1) have been synthesized. The X-ray structural analysis of {[Co(ClO4)(H2O)(L)][Co(H2O)2(L)]}(ClO4)3 shows two different metal sites in octahedral coordination. The EPR spectra of powdered samples of this compound are typical of distorted six-coordinated Co(II) ions in a high-spin (S=3/2) configuration, with the ground state being S=1/2 (g1=5.20, g2=3.20, g3=1.95). The EPR spectrum of [Cu(ClO4)(L)](ClO4) was simulated assuming an axial g tensor (g1=g2=2.043, g3=2.145), while that of [Cu(ClO4)(L1)](ClO4) slightly differs from an axial symmetry (g1=2.025, g2=2.060, g3=2.155). These results are compatible with a Cu(II) ion in square-pyramidal coordination with N2S2 as basal ligands. Single-crystal EPR experiment performed on [Cu(ClO4)(L1)](ClO4) allowed determining the eigenvalues of the molecular g tensor associated with the copper site, as well as the two possible orientations for the tensor. On the basis of symmetry arguments, an assignment in which the eigenvectors are nearly along the Cu(II)-ligand bonds is chosen.     

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.     

A new pyridine-based 12-membered macrocycle functionalised with different fluorescent subunits; coordination chemistry towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II)

The coordination chemistry of the new pyridine-based, N2S2-donating 12-membered macrocycle 2,8-dithia-5-aza-2,6-pyridinophane (L1) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) has been investigated both in aqueous solution and in the solid state. The protonation constants for L1 and stability constants with the aforementioned metal ions have been determined potentiometrically and compared with those of ligand L2, which contains a N-aminopropyl side arm. The measured values show that Hg(II) in water has the highest affinity for both ligands followed by Cu(II), Cd(II), Pb(II), and Zn(II). For each metal ion considered, 1:1 complexes with L1 have also been isolated in the solid state, those of Cu(II) and Zn(II) having also been characterised by X-ray crystallography. In both complexes L1 adopts a folded conformation and the coordination environments around the two metal centres are very similar: four positions of a distorted octahedral coordination sphere are occupied by the donor atoms of the macrocyclic ligand, and the two mutually cis-positions unoccupied by L1 accommodate monodentate NO3- ligands. The macrocycle L1 has then been functionalised with different fluorogenic subunits. In particular, the N-dansylamidopropyl (L3), N-(9-anthracenyl)methyl (L4), and N-(8-hydroxy-2-quinolinyl)methyl (L5) pendant arm derivatives of L1 have been synthesised and their optical response to the above mentioned metal ions investigated in MeCN/H2O (4:1 v/v) solutions.     

Dioxadiaza- and trioxadiaza-macrocycles containing one dibenzofuran unit selective for cadmium

The binding properties of dioxadiaza- ([17](DBF)N2O2) and trioxadiaza- ([22](DBF)N2O3), macrocyclic ligands containing a rigid dibenzofuran group (DBF), to metal cations and structural studies of their metal complexes have been carried out. The protonation constants of these two ligands and the stability constants of their complexes with Ca2+, Ba2+, and Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+, were determined at 298.2 K in methanol-water (1:1, v/v), and at ionic strength 0.10 mol dm-3 in KNO3. The values of the protonation constants of both ligands are similar, indicating that no cavity size effect is observed. Only mononuclear complexes of these ligands with the divalent metal ions studied were found, and their stability constants are lower than expected, especially for the complexes of the macrocycle with smaller cavity size. However, the Cd2+ complex with [17](DBF)N2O2 exhibits the highest value of stability constant for the whole series of metal ions studied, indicating that this ligand reveals a remarkable selectivity for cadmium(II) in the presence of all the metal ions studied, except copper(II), indicating that this ligand reveals a remarkable selectivity for cadmium(II) in the presence of the mentioned metal ions. The crystal structures of H2[17](DBF)N2O3(2+) (diprotonated form of the ligand) and of its cadmium complex were determined by X-ray diffraction. The Cd2+ ion fits exactly inside the macrocyclic cavity exhibiting coordination number eight by coordination to all the donor atoms of the ligand, and additionally to two oxygen atoms from one nitrate anion and one oxygen atom from a water molecule. The nickel(II) and copper(II) complexes with the two ligands were further studied by UV-vis-NIR and the copper(II) complexes also by EPR spectroscopic techniques in solution indicating square-pyramidal structures and suggesting that only one nitrogen and oxygen donors of the ligands are bound to the metal. However an additional weak interaction of the second nitrogen cannot be ruled out.     

Comparative study of donor atom effects on the thermodynamic and electron-transfer kinetic properties of copper(II/I) complexes with sexadentate macrocyclic ligands. [CuII/I([18]aneS4N2)] and [CuII/I([18]aneS4O2)

Studies have been conducted on the copper complexes formed with two sexadentate macrocyclic ligands containing four thioether sulfur donor atoms plus either two nitrogen or two oxygen donor atoms on opposing sides of the ring. The resulting two ligands, L, designated as [18]aneS(4)N(2) and [18]aneS(4)O(2), respectively, represent homologues of the previously studied Cu(ii/i) system with a macrocycle having six sulfur donor atoms, [18]aneS(6). Crystal structures of [Cu(II)([18]aneS(4)O(2))](ClO(4))(2) and [Cu(I)([18]aneS(4)O(2))]ClO(4) have been determined in this work. Comparison of the structures of all three systems reveals that the oxidized complexes are six coordinate with two coordinate bonds undergoing rupture upon reduction. However, the geometric changes accompanying electron transfer appear to differ for the three systems. The stability constants and electrochemical properties of both of the heteromacrocyclic complexes have been determined in acetonitrile and the Cu(II/I)L electron-transfer kinetics have been studied in the same solvent using six different counter reagents for each system. The electron self-exchange rate constants have then been calculated using the Marcus cross relationship. The results are compared to other Cu(II/I)L systems in terms of the effect of ligand geometric changes upon the overall kinetic behavior.     

Stabilities and Redox Properties of Cu(I) and Cu(II) Complexes with Macrocyclic Ligands Containing the N2S2 donor Set

The complexation of Cu(I) and Cu(II) by a series of 12-, 14- and 16-membered macrocyclic ligands 1–6 containing the N₂S₂ donor set has been studied potentiometrically, spectrophotometrically and voltammetrically. In the case of Cu(II), mononuclear complexes CuL²⁺ with stability constants of 10¹⁰–10¹⁵ are formed. In addition, partially hydrolyzed species Cu(L)OH⁺ are observed at pH > 10 for the 12-membered ligands. For Cu(I), beside the specis CuL⁺ with stabilities of 10¹²–10¹⁴, the unexpected formation of protonated species CuLH²⁺ was detected. In contrast to the well-known general trends in coordination chemistry, the stability of these protonated species increases relative to that of the complexes with the neutral ligand when the ring size and concomitantly the distance between neighbouring donor atoms is decreased. From the stability constants of the Cu(I)- and Cu(II)-complexes the redox potentials have been calculated and are compared to the values of E^1/2 obtained by cyclic voltammetry. Despite the identical donor set the Cu(II)/Cu(I) redox potentials of the complexes are spanning a range of 340 mV or six orders of magnitude in relative stability, reflecting the importance of subtle differences in steric requirements.     

Helical-chain copper(II) complexes and a cyclic tetranuclear copper(II) complex with single syn-anti carboxylate bridges and ferromagnetic exchange interactions

Tridentate Schiff-base carboxylate-containing ligands, derived from the condensation of 2-imidazolecarboxaldehyde with the amino acids beta-alanine (H2L1) and 2-aminobenzoic acid (H2L5) and the condensation of 2-pyridinecarboxaldehyde with beta-alanine (HL2), D,L-3-aminobutyric acid (HL3), and 4-aminobutyric acid (HL4), react with copper(II) perchlorate to give rise to the helical-chain complexes [[Cu(mu-HL1)(H2O)](ClO4)]n (1), [[Cu(mu-L2)(H2O)](ClO4).2H2O]n (2), and [[Cu(mu-L3)(H2O)](ClO4).2H2O]n (3), the tetranuclear complex [[Cu(mu-L4)(H2O)](ClO4)]4 (4), and the mononuclear complex [Cu(HL5)(H2O)](ClO4).1/2H2O (5). The reaction of copper(II) chloride with H2L1 leads not to a syn-anti carboxylate-bridged compound but to the chloride-bridged dinuclear complex [Cu(HL1)(mu-Cl)]2 (6). The structures of these complexes have been solved by X-ray crystallography. In complexes 1-4, roughly square-pyramidal copper(II) ions are sequentially bridged by syn-anti carboxylate groups. Copper(II) ions exhibit CuN2O3 coordination environments with the three donor atoms of the ligand and one oxygen atom belonging to the carboxylate group of an adjacent molecule occupying the basal positions and an oxygen atom (from a water molecule in the case of compounds 1-3 and from a perchlorate anion in 4) coordinated in the apical position. Therefore, carboxylate groups are mutually cis oriented and each syn-anti carboxylate group bridges two copper(II) ions in basal-basal positions with Cu...Cu distances ranging from 4.541 A for 4 to 5.186 A for 2. In complex 5, the water molecule occupies an equatorial position in the distorted octahedral environment of the copper(II) ion and the Cu-O carboxylate distances in axial positions are very large (>2.78 A). Therefore, this complex can be considered as mononuclear. Complex 6 exhibits a dinuclear parallel planar structure with Ci symmetry. Copper(II) ions display a square-pyramidal coordination geometry (tau = 0.06) for the N2OCl2 donor set, where the basal coordination sites are occupied by one of the bridging chlorine atoms and the three donor atoms of the tridentate ligand and the apical site is occupied by the remaining bridging chlorine atom. Magnetic susceptibility measurements indicate that complexes 1-4 exhibit weak ferromagnetic interactions whereas a weak antiferromagnetic coupling has been established for 6. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.     

Syntheses and molecular structures of three Cu(II) complexes with tetradentate imine-phenols

Three Cu(II) complexes of N,N′-bis-(salicylidene)-1,3-diiminopropane (1), N,N′-bis-(salicylidene)-1,3-diimino-2,2-dimethylpropane (2), and N,N′-bis-(salicylidene)-1,5-diiminopentane (3) have been prepared and characterized by X-ray diffraction. All of the three complexes are four coordinated with Cu(II) in a tetrahedrally distorted square-planar geometry to two imine N atoms and two phenolate O atoms. Both 1 and 2 are monomeric with a 6-6-6 chelate ring structure and display the 2N2O donor atoms in a normal, tetradentate “cis” configuration. However, in 3 two Cu(II) ions coordinate with bis-bidentate Schiff-base ligands, such that the Cu atoms are bridged by the two ligands; about each Cu atom, the arrangement of the iminophenolate groups is trans. The CuN1O1 and CuN2O2 planes intersect to form dihedral angles of 24.7° and 34.8° for 1 and 2, respectively, while the dihedral angle of two bidentate chelate planes of 3 is 40.5°.     

Formation and dissociation kinetics and crystal structures of nickel(II)-macrocyclic tetrathiaether complexes in acetonitrile. Comparison to nickel(II)-macrocyclic tetramines

Complex formation and dissociation rate constants have been independently determined for solvated nickel(II) ion reacting with eight macrocyclic tetrathiaether ligands and one acyclic analogue in acetonitrile at 25 degrees C, mu = 0.15 M. The macrocyclic ligands include 1,4,8,11-tetrathiacyclotetradecane ([14]aneS4) and seven derivatives in which one or both ethylene bridges have been substituted by cis- or trans-1,2-cyclohexane, while the acyclic ligand is 2,5,9,12-tetrathiatridecane (Me2-2,3,2-S4). In contrast to similar complex formation kinetic studies on Ni(II) reacting with corresponding macrocyclic tetramines in acetonitrile and N,N-dimethylformamide (DMF), the kinetics of complex formation with the macrocyclic tetrathiaethers show no evidence of slow conformational changes following the initial coordination process. The differing behavior is ascribed to the fact that such conformational changes require donor atom inversion, which is readily accommodated by thiaether sulfurs but requires abstraction of a hydrogen from a nitrogen (to form a temporary amide). The latter process is not facilitated in solvents of low protophilicity. The rate-determining step in the formation reactions appears to be at the point of first-bond formation for the acyclic tetrathiaether but shifts to the point of chelate ring closure (i.e., second-bond formation) for the macrocyclic tetrathiaether complexes. The formation rate constants for Ni(II) with the macrocyclic tetrathiaethers parallel those previously obtained for Cu(II) reacting with the same ligands in 80% methanol-20% water (w/w). By contrast, the Ni(II) dissociation rate constants show significant variations from the trends in the Cu(II) behavior. Crystal structures are reported for the Ni(II) complexes formed with all five dicyclohexanediyl-substituted macrocyclic tetrathiaethers. All but one are low-spin species.     

Copper(II) bromide complexes with acyclic and cyclic pyrimidine-containing phane ligands

Complexes of copper(II) bromide with cyclic and isostructural acyclic phane ligands containing derivatives of pyrimidine nucleobases (cytosine and uracil) were synthesized and characterized. In two cyclic pyrimidinophanes used, the macrocycles included two 6-methylthiocytosine and one 6-methyluracil units linked by polymethylene chains (L³) and two 6-methyluracil units linked by N-containing bridges (L⁵). Ligand L³ and its isostructural acyclic analogs are coordinated by the Cu²⁺ ion through the same donor sites (the ring N atoms of the thiocytosine units). The coordination polyhedra of the Cu atom in complexes with cyclic and acyclic ligands are different. Ligand L⁵ and its isostructural acyclic analog also form copper(II) complexes with different coordination polyhedra involving different donor sites. The acyclic ligand is coordinated by the Cu²⁺ ion via the bridging N atom, while cyclic ligand L⁵, via the uracil CO groups (the bridging N atoms become protonated). The resulting complexes are dielectrics.     

Effect of constrained donor atom orientations on the stabilities, complexation kinetics, redox potentials, and structures of macrocyclic polythiaether Complexes. Copper(II) complexes with cyclopentanediyl derivatives of [14]aneS4 in 80% methanol

The two ethylene bridges in the macrocyclic tetrathiaether 1,4,8,11-tetrathiacyclotetradecane ([14]aneS(4)) have been systematically replaced by cis- or trans-1,2-cyclopentane to generate a series of new ligands that exhibit differing preferences for the orientation of the sulfur donor atoms while maintaining constant inductive effects. The resulting five dicyclopentanediyl derivatives, along with two previously synthesized monocyclopentanediyl analogues, have been complexed with Cu(II), and their stability constants, formation and dissociation rate constants, and redox potentials have been determined in 80% methanol/20% water (by weight). The crystal structures of the Cu(II) complexes with the five dicyclopentanediyl-[14]aneS(4) diastereomers as well as the structures for a representative Cu(I) complex and one of the free ligands have also been determined. The properties of these complexes are compared to previous data obtained for the corresponding cyclohexanediyl derivatives in an attempt to shed additional light on the influence of sterically constraining substituents upon the properties of macrocyclic ligand complexes.     

Synthesis and characterization of nickel(II) complexes with potentially pentadentate macrocyclic ligands having N3O2 donor set

Nickel(II) complexes of N₃O₂ donor macrocycles incorporating 17- to 19-membered macrocyclic rings have been prepared. Physical measurements ind     

Synthesis,spectroscopic characterization and X-ray crystallographic studies of trans-[PtCl2(PEt3)(PySOR)] complexes,where PySOR = (2-methylsulphinyl)-pyridine and (2-n-propylsulphinyl)pyridine

Alkylsulphinylpyridine ligands containing three potential donor centres: N, S and O atoms and two complexes of general formula trans-[PtCl₂(PEt₃)PySOR)] (R = Me and ⁿ Pr) were prepared and characterized by elemental analysis, i.r. spectroscopy, ¹H- and ³¹P-n.m.r. and X-ray crystallography. The ambidentate ligands act in both situations as monodentate ligands, bonded to the metal exclusively through the nitrogen atom. The crystal structures revealed the occurrence of discrete molecules and, in both complexes, the Pt atoms are coordinated in square planar arrangements by two chloride ions, in a trans configuration, by the pyridine nitrogen atom, and by the phosphine P atom. The oxygen atoms do not take part in the complexation scheme.     

Synthesis,spectroscopic, electrochemical and structural characterization of Cu(II) complexes with asymmetric NN′OS coordination spheres

A set of four Cu(II) complexes, [Cu(cdnapen)], [Cu(cdnappd)], [Cu(cdMenappd)] and [Cu(cdMeMeOsalpd)], derived from Schiff base ligands with an asymmetric NN′OS coordination sphere have been synthesized. The molecular and the crystal structures have been determined by X-ray diffractometry. The structural results confirm that the complexes are tetra coordinated. The copper (II) ion coordinates to two nitrogen atoms from the imine moiety of the ligand, a sulfur atom from the methyl dithiocarboxylate moiety and a phenolic oxygen atom. The complexes show an unusual tetrahedral distortion to the square-planar geometry around the metal centre in spite of the pseudomacrocyclic skeleton of the ligand. The complexes were further characterized by cyclic voltammetry and electron paramagnetic resonance spectroscopy. The degree of tetrahedral distortion of the complexes appears to be dependent on the number of carbon atoms of the aliphatic bridge and the nature of the coordinating atoms.     

Spectral studies, cyclic voltammetry and synthesis of cobalt(II) and ruthenium(III) complexes with symmetric and asymmetric ring containing membered N2S2, N4, and N5 donor macrocyclic ligands

Reaction of divalent cobalt(II) and trivalent ruthenium(III) salts (NO3, SCN and SO4) with macrocyclic ligands L1, L2 and L3 having N2S2, N4 and N5 core, have been designed and carry out. All these three macrocyclic ligands and their complexes were obtained in pure form. Their structures were investigated by using microanalytical analyses, IR, mass, magnetic moments, electronic and EPR spectral studies. The redox properties of the complexes were also examined by cyclic voltammetry. An interesting feature of complexes is that the relatively large rings of macrocyclic ligands prevent the macrocyclic rings from approaching the metal center as closely as they would, if they were not constrained. So the Ru-N distances are longer than expected due to ring size. Electrochemical studies show that the macrocyclic ligand L1 is more effective electron donors to ruthenium than of L2 and L3. Electronic spectral properties also show that the sulphur donor atom of L1 weakens the ligand field with respect to ligand-to-metal charge-transfer band. However it is expected that second-row transition metal-ligand bonds tend to be weaker than third-row transition metal-ligand bonds. There are well-established examples of reactions in which decreased of reactivity down a triad of transition metals is not observed. These novelties are usually attributed to pi-bonding effects for ligands such as carbon monoxide, solvent effects, or a change in mechanism.     

Copper(II) hexaaza macrocyclic binuclear complexes obtained from the reaction of their copper(I) derivates and molecular dioxygen

Density functional theory (DFT) calculations have been carried out for a series of Cu(I) complexes bearing N-hexadentate macrocyclic dinucleating ligands and for their corresponding peroxo species (1c-8c) generated by their interaction with molecular O2. For complexes 1c-7c, it has been found that the side-on peroxodicopper(II) is the favored structure with regard to the bis(mu-oxo)dicopper(III). For those complexes, the singlet state has also been shown to be more stable than the triplet state. In the case of 8c, the most favored structure is the trans-1,2-peroxodicopper(II) because of the para substitution and the steric encumbrance produced by the methylation of the N atoms. Cu(II) complexes 4e, 5e, and 8e have been obtained by O2 oxidation of their corresponding Cu(I) complexes and structurally and magnetically characterized. X-ray single-crystal structures for those complexes have been solved, and they show three completely different types of Cu(II)2 structures: (a) For 4e, the Cu(II) centers are bridged by a phenolate group and an external hydroxide ligand. The phenolate group is generated from the evolution of 4c via intramolecular arene hydroxylation. (b) For 5e, the two Cu(II) centers are bridged by two hydroxide ligands. (c) For the 8e case, the Cu(II) centers are ligated to terminally bound hydroxide ligands, rare because of its tendency to bridge. The evolution of complexes 1c-8c toward their oxidized species has also been rationalized by DFT calculations based mainly on their structure and electrophilicity. The structural diversity of the oxidized species is also responsible for a variety of magnetic behavior: (a) strong antiferromagnetic (AF) coupling with J = -482.0 cm(-1) (g = 2.30; rho = 0.032; R = 5.6 x 10(-3)) for 4e; (b) AF coupling with J = -286.3 cm(-1) (g = 2.07; rho = 0.064; R = 2.6 x 10(-3)) for 5e; (c) an uncoupled Cu(II)2 complex for 8e.     

Thermodynamic and electron-transfer properties of copper(II/I) polyaminothiaether complexes

In electron-transfer reactions, the change in the oxidation states of the reactants is generally accompanied by structural changes, which influence the electron-transfer kinetics. Previous studies on the systems of Cu(II)/(I) complexes involving cyclic tetrathiaether ligands indicated that inversion of coordinated donor atoms is a major geometric change during the overall electron-transfer process. Complex formation and isomerization studies on complexes with the 1,4,8,11-tetraazacyclotetradecane ligand have demonstrated that a necessary condition for conformational change is deprotonation followed by inversion of coordinated N atoms. When one or more nitrogen donor atoms in a ligand are replaced with sulfur, there is a choice of N or S inversion. It has been hypothesized that donor atom inversion (N or S donors) is a major factor that can lead to conformationally limited electron-transfer kinetics of copper systems. In the current study, the thermodynamic properties, electron-transfer kinetics and conformational changes in copper(II)[1,4,8-trithia-11-azacyclotetradecane], copper(II)[1,8-dithia-4,11-diazacyclotetradecane] and copper(II)[1,11,-dithia-4,8-diazacyclotetradecane] were determined in order to determine the effect of inversion of coordinated N atoms on electron-transfer rates as a function of low concentrations of water in an aprotic solvent (acetonitrile). By using controlled amounts of water as a hydrogen ion acceptor, deprotonation of amine nitrogen and nitrogen donor inversion was followed by comparing self-exchange rate constants for reduction and oxidation of the copper complexes. Data on thermodynamic properties and electron-transfer kinetics are presented. Possible conformational changes and kinetic pathways for complexes with ligands having mixed N and S donor sets are presented.     

Design of base metal extractants. Part 1. Inter-ligand hydrogen bonding in the assembly of pseudo-macrocyclic bis(aminosulfonamidato)M(II) complexes

Monosulfonyl derivatives of simple 1,2- and 1,3-diamines (R2HN-R-NHSO2R1 = L) have been shown to be easily deprotonated to give neutral 2:1 complexes, [M(L - H)(2)], with Co(II), Ni(II), Cu(II) or Zn(II). The Ni(II) and Cu(II) complexes with deprotonated N-tosyl-1,2-diaminoethane have a planar N4(2-) donor set and a 14-membered pseudo-macrocyclic structure based on head-to-tail S=O...H-N((amine)) bonding between the two bidentate ligands. In the related tetrahedral Zn(II) complex the ends of the mutually perpendicular bidentate N2- units are too far apart to form a cyclic H-bonded system. X-Ray structure determinations on five free ligands provide evidence for extensive inter-molecular H-bonding, which in the case of N-tosyl-1,3-diaminopropane and its N'-tert-butyl derivative involves formation of dimeric 16-membered pseudo-macrocycles. Despite favourable inter-ligand H-bonding in the neutral 2:1 complexes, these ligands are relatively weak extractants, showing >50% loading of Cu(II) in "pH-swing" equilibria, 2L(org)+ M2+ = [M(L - H)2](org)+ 2 H+, only when the pH of the aqueous phase is raised above 4.