Heterobimetallic activation of dioxygen: characterization and reactivity of novel Cu(I)-Ge(II) complexes

Reaction of the known germylene Ge[N(SiMe3)2]2 and a new heterocyclic variant Ge[(NMes)2(CH)2] with [L(Me2)Cu]2 (L(Me2) = the beta-diketiminate derived from 2-(2,6-dimethylphenyl)amino-4-(2,6-dimethylphenyl)imino-2-pentene) yielded novel Cu(I)-Ge(II) complexes L(Me2)Cu-Ge[(NMes)2(CH)2] (1a) and L(Me2)Cu-Ge[N(SiMe3)2]2 (1b), which were characterized by spectroscopy and X-ray crystallography. The lability of the Cu(I)-Ge(II) bond in 1a and b was probed by studies of their reactivity with benzil, PPh3, and a N-heterocyclic carbene (NHC). Notably, both complexes are cleaved rapidly by PPh3 and the NHC to yield stable Cu(I) adducts (characterized by X-ray diffraction) and the free germylene. In addition, the complexes are highly reactive with O2 and exhibit chemistry which depends on the bound germylene. Thus, oxygenation of 1a results in scission and formation of thermally unstable L(Me2)CuO2, which subsequently decays to [(L(Me2)Cu)2(mu-O)2], while 1b yields L(Me2)Cu(mu-O)2Ge[N(SiMe3)2]2, a novel heterobimetallic intermediate having a [Cu(III)(mu-O)2Ge(IV)]3+ core. The isolation of the latter species by direct oxygenation of a Cu(I)-Ge(II) precursor represents a new route to heterobimetallic oxidants comprising copper.     

COPPER(II) PROPIONATES Crystal and Molecular Structure of Bis(propionato)copper(II) Di(methyl-3-pyridylcarbamate)

Abstract

New copper(II) propionate compounds of composition Cu(prop)₂L (L =methyl-3-pyridylcarbamate or N, N-diethylnikotinamide) andau(prop)₂L₂ (L = methyl-3-pyr-idylcarbamate or2, 6-pyridinemethanole) have been prepared. The crystal and molecular structure of thetetrakis(μ-propionato)di(methyl-3-pyridinecarbamate) dicopper(II), Cu-₂(prop)₄(mpc)₂, was determined by direct method and Fouriertechniques. The compound crystallizes in the orthorhombic space group Pcab with four dimeric units in a cell withdimensions a = 19.350(4), b = 15.390(3), c = 10.725(2)Å. The structure was refined byfull-matrix least-squares methods to a R factor of 0.031, based on 3666 independent reflections. Thecompound is dimeric, with square-pyramidal geometry at each copper centre. The two copper atoms are bridgedby four carboxylate groups, while the apical ligands are methyl-3-pyridylcarbamate. The structural dataare compared with those found in similar copper(II) propionates. Spectral data of Cu(prop)₂L aretypical for dimeric copper(II) compounds. Both Cu(prop)₂L₂ compounds seem to possessoctahedral cop-per(II) stereochemistry with differing tetragonal distortion.     

Nitric oxide reactivity of copper(II) complexes of bidentate amine ligands: effect of chelate ring size on the stability of a [Cu(II)-NO] intermediate

Three copper(II) complexes, 1, 2, and 3 with L(1), L(2) and L(3) [L(1) = 2-(2-aminoethyl)-pyridine; L(2) = 2-(N-ethyl-2-aminoethyl)-pyridine; L(3) = 3,3'-iminobis(N,N-dimethylpropylamine)], respectively, were synthesized and characterized. Addition of nitric oxide gas to the degassed acetonitrile solution of the complexes were found to result in the reduction of the copper(II) center to copper(I). In cases of complexes 1 and 2, the formation of the [Cu(II)-NO] intermediate prior to the reduction of Cu(II) was evidenced by UV-visible, solution FT-IR and X-band EPR spectroscopic studies. However, for complex 3, the formation of [Cu(II)-NO] has not been observed. DFT calculations on the [Cu(II)-NO] intermediate generated from complex 1 suggest a distorted square pyramidal geometry with the NO ligand coordinated to the Cu(II) center at an equatorial site in a bent geometry. In the case of complex 1, the reduction of the copper(II) center by nitric oxide afforded ligand transformation through diazotization at the primary amine site in acetonitrile solution; whereas, in an acetonitrile-water mixture, it resulted in 2-(pyridine-2-yl)ethanol. On the other hand, in cases of complexes 2 and 3, it was found to yield N-nitrosation at the secondary amine site in the ligand frameworks. The final organic products, in each case, were isolated and characterized by various spectroscopic studies.     

Copper(II)-mediated oxidative transformation of vic-dioxime to furoxan: evidence for a copper(II)-dinitrosoalkene intermediate

The mononuclear copper(II) complex [Cu(H(2)L(1))(2)(H(2)O)](ClO(4))(2) (1) (where H(2)L(1) = 1,10-phenanthroline-5,6-dioxime) reacts with copper(II) perchlorate in acetonitrile at ambient conditions in the presence of triethylamine to afford a copper(II) complex, [Cu(L(3))(2)(H(2)O)](ClO(4))(2) (2a), of 1,10-phenanthroline furoxan. A similar complex [Cu(L(3))(2)Cl](ClO(4)) (2) is isolated from the reaction of H(2)L(1) with copper(II) chloride, triethylamine, and sodium perchlorate in acetonitrile. The two-electron oxidation of the vic-dioxime to furoxan is confirmed from the X-ray single crystal structure of 2. An intermediate species, showing an absorption band at 608 nm, is observed at -20 °C during the conversion of 1 to 2a. A similar blue intermediate is formed during the reaction of [Cu(HDMG)(2)] (H(2)DMG = dimethylglyoxime) with ceric ammonium nitrate, but H(2)DMG treated with ceric ammonium nitrate does not form any intermediate. This suggests the involvement of a copper(II) complex in the intermediate step. The intermediate species is also observed during the two-electron oxidation of other vic-dioximes. On the basis of the spectroscopic evidence and the nature of the final products, the intermediate is proposed to be a mononuclear copper(II) complex ligated by a vic-dioxime and a dinitrosoalkene. The dinitrosoalkene is generated upon two-electron oxidation of the dioxime. The transient blue color of the dioxime-copper(II)-dinitrosoalkene complex may be attributed to the ligand-to-ligand charge transfer transition. The intermediate species slowly decays to the corresponding two-electron oxidized form of vic-dioxime, i.e. furoxan and [Cu(CH(3)CN)(4)](ClO(4)). The formation of two isomeric furoxans derived from the reaction of an asymmetric vic-dioxime, hexane-2,3-dioxime, and copper(II) perchlorate supports the involvement of a dinitrosoalkene species in the intermediate step. In addition, the oxidation of 2,9-dimethyl-1,10-phenanthroline-5,6-dioxime (H(2)L(2)) to the corresponding furoxan and subsequent formation of a copper(I) complex [Cu(L(4))(2)](ClO(4)) (3) (where L(4) = 2,9-dimethyl-1,10-phenanthroline furoxan) are discussed.     

Mononuclear and binuclear copper(I) complexes ligated by bis(3,5-diisopropyl-1-pyrazolyl)methane: insight into the fundamental coordination chemistry of three-coordinate copper(I) complexes with a neutral coligand

By using the neutral bidentate nitrogen-containing ligand, bis(3,5-diisopropyl-1-pyrazolyl)methane (L1' '), the copper(I) complexes [Cu(L1' ')2](CuCl2) (1CuCl2), [Cu(L1' ')2](ClO4) (1ClO4), [Cu(L1' ')]2(ClO4)2 (2ClO4), [Cu(L1' ')]2(BF4)2 (2BF4), [Cu(L1' ')(NCMe)](PF6) (3PF6), [Cu(L1' ')(PPh3)](ClO4) (4ClO4), [Cu(L1' ')(PPh3)](PF6) (4PF6), [{Cu(L1' ')(CO)}2(mu-ClO4)](ClO4) (5ClO4), and the copper(II) complexes [{Cu(L1' ')}2(mu-OH)2(mu-ClO4)2] (6), and [Cu(L1' ')Cl2] (7) were systematically synthesized and fully characterized by X-ray crystallography and by IR and 1H NMR spectroscopy. In the case of copper(II), ESR spectroscopy was also applied. In comparison with the related neutral tridentate ligand L1', bis-chelated copper(I) complexes and binuclear linear-coordinated copper(I) complexes are easy to obtain with L1' ', like 1CuCl2, 1ClO4, 2ClO4, and 2BF4. Importantly, stronger and bulkier ligands such as acetonitrile (3PF6) and especially triphenylphosphine (4ClO4 and 4PF6) generate three-coordinate structures with a trigonal-planar geometry. Surprisingly, for the smaller ligand carbon monoxide, a mononuclear three-coordinate structure is very unstable, leading to the formation of a binuclear complex (5ClO4) with one bridging perchlorate anion, such that the copper(I) centers are four-coordinate. The same tendency is observed for the copper(II) bis(mu-hydroxo) compounds 6, which is additionally bridged by two perchlorate anions. Both copper(II) complexes 6 and 7 were obtained by molecular O2 oxidation of the corresponding copper(I) complexes. A comparison of the new copper(I) triphenylphosphine complexes 4ClO4 and 4PF6 with corresponding species obtained with the related tridentate ligands L1' and L1 (8ClO4 and 9, respectively) reveals surprisingly small differences in their spectroscopic properties. Density functional theory (DFT) calculations are used to shed light on the differences in bonding in these compounds and the spectral assignments. Finally, the reactivity of the different bis(pyrazolyl)methane complexes obtained here toward PPh3, CO, and O2 is discussed.     

Copper(II) mediated anion dependent formation of Schiff base complexes

A tetranuclear mixed ligand copper(II) complex of a pyrazole containing Schiff base and a hydroxyhexahydropyrimidylpyrazole and copper(II) and nickel(II) complexes of the Schiff base having N-donor atoms have been investigated. A 2 equiv amount of 5-methyl-3-formylpyrazole (MPA) and 2 equiv of 1,3-diamino-2-propanol (1,3-DAP) on reaction with 1 equiv of copper(II) nitrate produce an unusual tetranuclear mixed ligand complex [Cu4(L1)2(L2)2(NO3)2] (1), where H2L1 = 1,3-bis(5-methyl-3-formylpyrazolylmethinimino)propane-2-ol and HL2 = 5-methyl-3-(5-hydroxyhexahydro-2-pyrimidyl)pyrazole. In contrast, a similar reaction with nickel(II) nitrate leads to the formation of a hygroscopic intractable material. On the other hand, the reaction involving 2 equiv of MPA and 1 equiv each of 1,3-DAP and various copper(II) salts gives rise to two types of products, viz. [Cu(T3-porphyrinogen)(H2O)]X2 (X = ClO4, NO3, BF4 (2)) (T3-porphyrinogen = 1,6,11,16-tetraza-5,10,15,20-tetrahydroxy-2,7,12,17-tetramethylporphyrinogen) and [Cu(H2L1)X]X x H2O (X = Cl (3), Br (4)). The same reaction carried out with nickel(II) salts also produces two types of compounds [Ni(H2L1)(H2O)2]X2 [X = ClO4 (5), NO3 (6), BF4 (7)] and [Ni(H2L1)X2] x H2O [X = Cl (8), Br (9)]. Among the above species 1, 3, and 5 are crystallographically characterized. In 1, all four copper atoms are in distorted square pyramidal geometry with N4O chromophore around two terminal copper atoms and N5 chromophore around two inner copper atoms. In 3, the copper atom is also in distorted square pyramidal geometry with N4Cl chromophore. The nickel atom in 5 is in a distorted octahedral geometry with N4O2 chromophore, where the metal atom is slightly pulled toward one of the axial coordinated water molecules. Variable-temperature (300 to 2 K) magnetic susceptibility measurements have been carried out for complex 1. The separations between the metal centers, viz., Cu(1)...Cu(2), Cu(2)...Cu(2)A, and Cu(2)A...Cu(1)A are 3.858, 3.89, and 3.858 A, respectively. The overall magnetic behavior is consistent with strong antiferromagnetic interactions between the spin centers. The exchange coupling constants between Cu(1)...Cu(2) and Cu(2)...Cu(2A) centers have turned out to be -305.3 and -400.7 cm(-1), respectively, resulting in a S = 1/2 ground state. The complexes are further characterized by UV-vis, IR, electron paramagnetic resonance, and electrochemical studies.     

Synthesis, crystal structure, and magnetic properties of oxime-bridged polynuclear Ni(II) and Cu(II) complexes

Two new polynuclear complexes [Ni6(amox)6(mu6-O)(mu3-OH)2](Cl2).6H2O and [Cu3(amox)3(mu3-OH)(mu3-Cl)](ClO4).4H2O (amox- = anion of 4-amino-4-methyl-2-pentanone oxime) have been synthesized and characterized structurally and magnetically. The Ni(II) complex contains a novel Chinese-lantern-like Ni6 cage centered by an oxo ion. It contains the nearest octahedral Ni(II)...Ni(II) separation (<2.8 A) and exhibits strong antiferromagnetic properties. The Cu(II) complex has a cyclic trinuclear copper(II) core bridged by both mu3-OH(-) and mu3-Cl(-) ions. The magnetic susceptibilities of both antiferromagnetic complexes were fitted by using approximate models.     

Synthesis and structural characterization of a novel mixed-valent Cu(II)Cu(I)Cu(II) triangular metallomacrocycle using an imine-based rigid ligand

A novel neutral mixed-valent Cu(I)Cu(II)(2) triangular metallomacrocycle [Cu(3)L(2)(HL)].3CH(3)OH.2H(2)O (1) was assembled by reaction of the tetradentate ligand bis(N-salicylidene-4,4'-diphenylamine), H(2)L, with a copper(II) salt. ESI-MS show peaks only corresponding to the triangular structural species, indicating the high stability of the trimer structure in solution. Magnetic study confirms that there are two Cu(II) ions and one Cu(I) ion in a discrete triangular molecule. The crystal structure of 1 reveals that the triangle is formed by three deprotonated ligands and three copper ions with a Cu-Cu separation of ca. 11.8 A. Each copper atom is coordinated by two oxygen atoms and two nitrogen atoms from two different bis-bidentate ligands in a heavily distorted tetrahedral geometry, while each ligand is bound to two metal ions in a bis-bidentate coordination mode and links the metal centers overlapping in an unprogressive manner. Strong intramolecular pi.pi interactions between the ligands are found to stabilize the constraint conformation of the triangle. Electrochemical study reveals that the mixed-valent Cu(I)Cu(II)(2) complex is the most stable state in solution condition, and the electrochemical communication between the copper ions might be explained on the basis of the through-bond interaction. UV-vis-NIR spectral measurement demonstrates the Robin-Day class II behavior of the mixed-valence compound with a weak copper-copper interaction.     

Copper(II) coordination chemistry of westiellamide and its imidazole, oxazole, and thiazole analogues

The copper(II) coordination chemistry of westiellamide (H(3)L(wa)), as well as of three synthetic analogues with an [18]azacrown-6 macrocyclic structure but with three imidazole (H(3)L(1)), oxazole (H(3)L(2)), and thiazole (H(3)L(3)) rings instead of oxazoline, is reported. As in the larger patellamide rings, the N(heterocycle)-N(peptide)-N(heterocycle) binding site is highly preorganized for copper(II) coordination. In contrast to earlier reports, the macrocyclic peptides have been found to form stable mono- and dinuclear copper(II) complexes. The coordination of copper(II) has been monitored by high-resolution electrospray mass spectrometry (ESI-MS), spectrophotometric and polarimetric titrations, and EPR and IR spectroscopies, and the structural assignments have been supported by time-dependent studies (UV/Vis/NIR, ESI-MS, and EPR) of the complexation reaction of copper(II) with H(3)L(1). Density functional theory (DFT) calculations have been used to model the structures of the copper(II) complexes on the basis of their spectroscopic data. The copper(II) ion has a distorted square-pyramidal geometry with one or two coordinated solvent molecules (CH(3)OH) in the mononuclear copper(II) cyclic peptide complexes, but the coordination sphere in [Cu(H(2)L(wa))(OHCH(3))](+) differs from those in the synthetic analogues, [Cu(H(2)L)(OHCH(3))(2)](+) (L = L(1), L(2), L(3)). Dinuclear copper(II) complexes ([Cu(II) (2)(HL)(mu-X)](+); X = OCH(3), OH; L = L(1), L(2), L(3), L(wa)) are observed in the mass spectra. While a dipole-dipole coupled EPR spectrum is observed for the dinuclear copper(II) complex of H(3)L(3), the corresponding complexes with H(3)L (L = L(1), L(2), L(wa)) are EPR-silent. This may be explained in terms of strong antiferromagnetic coupling (H(3)L(1)) and/or a low concentration of the dicopper(II) complexes (H(3)L(wa), H(3)L(2)), in agreement with the mass spectrometric observations.     

Reporting a unique example of electronic bistability observed in the form of valence tautomerism with a copper(II) helicate of a redox-active nitrogenous heterocyclic ligand

Valence tautomeric compounds involving nondixolene-type ligands are rare. The triple-helicate copper(II) complex [Cu(II)(2)(L)(3)](ClO(4))(4)·3CH(3)CN (1) containing a redox-active N-heterocyclic ligand (L) has been prepared and displays VT equilibrium in solution, as established by electronic spectroscopy, electron paramagnetic resonance spectroscopy, and cyclic and differential pulse voltammetry carried out at variable temperatures. The process involves intramolecular transfer of an electron from one of the L ligands to a copper(II) center, leading to the oxidation of L to an L(?+) radical with concomitant reduction of the Cu(II) center to Cu(I), as shown by the equilibrium [Cu(II)Cu(I)L(?+)L(2)](4+) ? [Cu(II)(2)L(3)](4+).     

Complex of bis(hexafluoroacetylacetonato)copper(II) with a stable acyclic nitroxide (tert-butyl)(3-keto-2-methylbutyl-2) nitroxyl oxime

A complex of bis(hexafluoroacetylacetonato)copper(II) with a stable acyclic nitroxide (tert-butyl)(3-keto-2-methylbutyl-2)nitroxyl oxime (L), Cu(hfac)₂L, has been synthesized. The structure of the complex was studied by X-ray diffraction analysis. The compound has a molecular structure with chelate coordination of the nitroxide. The tetragonally distorted octahedral environment of the copper(II) ion is formed by the oxygen atoms of the hfac anions and by the nitrogen and oxygen atoms of the oxime and nitroxyl groups of L, respectively. The nitroxyl group lies in the equatorial plane of the octahedron (d_Cu?O=1.907 Å). This type of N?O coordination leads to strong antiferromagnetic exchange interactions between the unpaired electrons of the copper(II) ion and the coordinated nitroxyl group and, as a consequence, to diamagnetism of Cu(hfac)₂L.     

Models for copper proteins. Copper(I) and (II) complexes of a novel binucleating tetraamino-tetrathioether ligand

The novel binucleating ligand, 6,6 prime-methylene-bis(5 prime-amino-3 prime,4 prime-benzo-2 prime-thiapentyl)-1,11-diamino-2,3:9,10-dibenzo-4,8-dithiaundecane (H4L) was prepared and reacted with copper(II) salts in dry MeOH to yield mixtures of copper(I) and copper(II) complexes with Cl- and ClO-4 counter ions. The amine functions on the ligand release protons to form copper(I) complexes: (Cu2L)X2, where X=Cl−, ClO4-. The complexes were oxidized to (Cu2L)X4 with H2O2 in DMF; Cu(NO3)2 gave a different complex, [Cu2(H4L)(NO3)2](NO3)2, as regards proton releasing ability, coordination and oxidation number. Evidence for the structures of this new tetraamino-tetrathioether ligand and its copper complexes is provided by 1H-, 13C-n.m.r., mass, u.v.–vis., i.r. spectra, elemental analyses, molar conductivities and magnetic moments. This revised version was published online in June 2006 with corrections to the Cover Date.     

A rational design for imidazolate-bridged linear trinuclear compounds from mononuclear copper(II) complexes with 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL): syntheses, structures, and magnetic properties of [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = ZnII, CuII, MnII)

Two mononuclear copper(II) complexes with the unsymmetrical tridentate ligand 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL), [Cu(HL)(H2O)](ClO4)2.2H2O (1) and [Cu(HL)Cl2] (2), have been prepared and characterized. The X-ray analysis of 2 revealed that the copper(II) ion assumes a pentacoordinated square pyramidal geometry with an N3Cl2 donor set. When 1 and 2 are treated with an equimolecular amount of potassium hydroxide, the deprotonation of the imidazole moiety promotes a self-assembled process, by coordination of the imidazolate nitrogen atom to a Cu(II) center of an adjacent unit, leading to the polynuclear complexes [[Cu(L)(H2O)](ClO4)]n (3) and [[Cu(L)Cl].2H2O]n (4). Variable-temperature magnetic data are well reproduced for one-dimensional infinite regular chain systems with J = -60.3 cm(-1) and g = 2.02 for 3 and J = -69.5 cm(-1) and g = 2.06, for 4. When 1 is used as a "ligand complex" for [M(hfac)2] (M = Cu(II), Ni(II), Mn(II), Zn(II)) in a basic medium, only the imidazolate-bridged trinuclear complexes [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = Zn(II), Cu(II)) (5, 6) can be isolated. Nevertheless, the analogous complex containing Mn(II) as the central metal (7) can be prepared from the precursor [Cu(HL)Cl2] (2). All the trinuclear complexes are isostructural. The structures of 5 and 6 have been solved by X-ray crystallographic methods and consist of well-isolated molecules with Ci symmetry, the center of symmetry being located at the central metal. Thus, the copper(II) fragments are in trans positions, leading to a linear conformation. The magnetic susceptibility data (2-300 K), which reveal the occurrence of antiferromagnetic interactions between copper(II) ions and the central metal, were quantitatively analyzed for symmetrical three-spin systems to give the coupling parameters JCuCu = -37.2 and JCuMn = -3.7 cm(-1) with D = +/-0.4 cm(-1) for 6 and 7, respectively. These magnetic behaviors are compared with those for analogous systems and discussed on the basis of a localized-orbital model of exchange interactions.     

Endogenous arene hydroxylation promoted by copper(I) cluster helicates

A novel neutral triple-stranded hexanuclear copper(I) cluster helicate [Cu(I)(6)L(3)]·2CH(3)CN derived from a thiosemicarbazone ligand could be synthesized and crystallographically characterized. The MALDI mass spectrum of this complex suggests that the tetranuclear copper(I) cluster helicate [Cu(I)(4)L(2)] is also present in solution. These copper(I) cluster helicates are capable, in the presence of O(2), of hydroxylating the arene linker of their supporting ligand strands. The resulting dinuclear complex [Cu(II)(2)L'(OH)] is formed by two copper(II) centers, a new ligand arising from the hydroxylation reaction, and one hydroxide group. The magnetic investigation of this compound shows a strong antiferromagnetic coupling between the two Cu(II) centers. The kinetic studies for the hydroxylation process show values of ΔH(≠)=-70 kJ mol(-1), similar to those mediated by the tyrosinase enzymes.     

Synthesis, spectroscopic and redox properties of the copper(II) complexes of N-(di-methylphenyl)-3,5-Bu2t-salicylaldimines

A series of copper(II) complexes (CuL2x) with new N-di-methylphenyl-3,5-Bu2t-salicylaldimines (L(x)H) were prepared and characterized by IR, UV/vis, 1H NMR, ESR, cyclic voltammetry techniques and chemical oxidation. L(x)H ligands have been found selectively bind to a Cu(II), rather than to Ni(II), Co(II), Mn(II), VO(IV), Zn(II) and Cd(II). ESR examinations of the CuL2x complexes demonstrate that they exist in magnetically diluted mononuclear or coupled triplet-state structures in the solid. The temperature dependent (113-283 K) intensity of the powder ESR spectra for some CuL2x is characteristic of ferromagnetic coupling (J > 0). The reduction potentials of CuL2x in DMSO are sensitive to aniline moieties. Chemical oxidation of CuL2x with (NH4)2[Ce(NO3)6] in CHCl3 and MeCN solutions at 300 K affords gradually disappearance of their ESR signals and dramatic changes in the electronic spectra as well as the appearance of new maximum bands at 530-672 (CHCl3) and 670-700 nm (MeCN), suggesting generation of Cu(II)-phenoxyl radical species.     

An unusual open cubane structure in a mu(1,1)-azido- and alkoxo-bridged tetranuclear copper(II) complex, [Cu4L2(mu(1,1)-N3)2].5H2O (H3L = N,N'-(2-Hydroxylpropane-1,3-diyl)bis-salicylideneimine)

A new end-on (EO) azido-bridged tetranuclear copper(II) complex [Cu(4)L(2)(mu(1,1)-N(3))(2)].5H(2)O derived from the ligand H(3)L (N,N'-(2-hydroxylpropane-1,3-diyl)bis-salicylideneimine) has been synthesized. Its X-ray structure shows an unusual Cu(4)O(2)N(2) open cubane core in which four copper(II) atoms are connected two by two through two mu(1,1)-azido species and three by three through two alkoxo bridges. The magnetic susceptibility data is dominated by strong antiferromagnetic interactions associated with the alkoxides and weak ferromagnetic interactions arising from the azides, in agreement with magneto-structural correlations found in the literature relative to such bridges in Cu(II) complexes.     

Synthesis, redox, and amphiphilic properties of responsive salycilaldimine-copper(II) soft materials

Hydrolysis of the asymmetric pyridine- and phenol-containing ligand HL (1) (2-hydroxy-4-6-di- tert-butylbenzyl-2-pyridylmethyl)imine) led to the use of bis-(3,5-di -tert-butyl-2-phenolato-benzaldehyde)copper(II), [Cu (II)(L (SAL)) 2] ( 1) as a precursor for bis-(2,4-di- tert-butyl-6-octadecyliminomethyl-phenolato)copper(II), [Cu (II)(L (2)) 2] ( 3), bis-(2,4-di- tert-butyl-6-octadecyl aminomethyl-phenolato)copper(II), [Cu (II)(L (2A)) 2] ( 3'), and bis-(2,4-di- tert-butyl-6-[(3,4,5-tris-dodecyloxy-phenylimino)-methyl]-phenolato)copper(II), [Cu (II)(L (3)) 2] ( 4). These complexes exhibit hydrophilic copper-containing head groups, hydrophobic alkyl and alkoxo tails, and present potential as precursors for redox-responsive Langmuir-Blodgett films. All systems were characterized by means of elemental, spectrometric, spectroscopic, and electrochemical techniques, and their amphiphilic properties were probed by means of compression isotherms and Brewster angle microscopy. Good redox activity was observed for 3 with two phenoxyl radical processes between 0.5 and 0.8 V vs Fc (+)/Fc, but this complex lacks amphiphilic behavior. To attain good balance between redox response and amphiphilicity, increased core flexibility in 3' and incorporation of alkoxy chains in 4 were attempted. Film formation with collapse at 14 mN.m (-1) was observed for the alkoxy-derivative but redox-response was seriously compromised. Core flexibility improved Langmuir film formation with a higher formal collapse and showed excellent cyclability of the ligand-based processes.     

EPR characterisation of Cu(II) complexes of poly(propylene imine) dendromesogens: using the orienting effect of a magnetic field.

Liquid-crystalline derivatives of poly(propylene imine)dendrimers of the 0th, 1st and 2nd generations, complexed with copper(II) ions, were studied by EPR spectroscopy. The structures of copper (II) complexes with different Cu(II) loadings x per dendrimer ligand L (x = Cu/L) were determined. At the lowest concentration, the Cu(II) ions form monomeric complexes with approximately square-planar N2O2 coordination of both carbonyl oxygen and amido nitrogen atoms. At higher copper content, two kinds of Cu(II) complex sites with different geometries exist. The orienting effect of a high magnetic field was used to investigate the structure and magnetic properties of the copper(II) complexes. This effect, for the first time in dendrimers, allowed the resolution of five nitrogen super-hyperfine lines on g(z) components with the unusual coupling constant of a(Nz)= 35.9 x 10(-4) cm(-1). The combination of the magnetic parameters and the orienting effect indicates the presence of a monomeric complex with pseudotetrahedral N2O2 coordination of the Cu(II) ion, as well as a "dimer" structure with fivefold coordination, presumably due to an N3O2 environment. Higher copper loadings lead to increased exchange coupling between the complex sites.     

Dinuclear cobalt(II) and copper(II) complexes with a Py2N4S2 macrocyclic ligand

The interaction between Co(II) and Cu(II) ions with a Py(2)N(4)S(2)-coordinating octadentate macrocyclic ligand (L) to afford dinuclear compounds has been investigated. The complexes were characterized by microanalysis, conductivity measurements, IR spectroscopy and liquid secondary ion mass spectrometry. The crystal structure of the compounds [H(4)L](NO(3))(4), [Cu(2)LCl(2)](NO(3))(2) (5), [Cu(2)L(NO(3))(2)](NO(3))(2) (6), and [Cu(2)L(μ-OH)](ClO(4))(3)·H(2)O (7) was also determined by single-crystal X-ray diffraction. The [H(4)L](4+) cation crystal structure presents two different conformations, planar and step, with intermolecular face-to-face π,π-stacking interactions between the pyridinic rings. Complexes 5 and 6 show the metal ions in a slightly distorted square-pyramidal coordination geometry. In the case of complex 7, the crystal structure presents the two metal ions joined by a μ-hydroxo bridge and the Cu(II) centers in a slightly distorted square plane or a tetragonally distorted octahedral geometry, taking into account weak interactions in axial positions. Electron paramagnetic resonance spectroscopy is in accordance with the dinuclear nature of the complexes, with an octahedral environment for the cobalt(II) compounds and square-pyramidal or tetragonally elongated octahedral geometries for the copper(II) compounds. The magnetic behavior is consistent with the existence of antiferromagnetic interactions between the ions for cobalt(II) and copper(II) complexes, while for the Co(II) ones, this behavior could also be explained by spin-orbit coupling.