Fluorescent nitric oxide detection by copper complexes bearing anthracenyl and dansyl fluorophore ligands

Anthrancenyl and dansyl fluorophore ligands [AnCH2pipCS(2)K (1), Ds-Hen (2), Ds-HAMP (3), Ds-HAQ (4), and Ds-HAPP (5)] were prepared for coordination to Cu(II). Five Cu complexes, [Cu(AnCH2pipCS2)2] (6), [Cu(Ds-en)2] (7), [Cu(Ds-AMP)2] (8), [Cu(Ds-AQ)2] (9), and [Cu(Ds-APP)(OTf)] (10), were synthesized as candidates for detecting nitric oxide (NO) by fluorescence and characterized by X-ray crystallography. A decrease in fluorescence compared to that of the free ligands (1-5) was measured following the formation of the corresponding five Cu(II) complexes 6-10. Fluorescence was restored in the presence of NO in CH3OH/CH2Cl2 solutions of the compounds. Complexes 7, 8, and 10 exhibited a fluorescence response to NO in pH 7.0 or 9.0 buffered aqueous solutions. Spectroscopic studies revealed that NO-induced fluorescence enhancement in these Cu(II) complexes occurs by reduction to Cu(I). The present studies demonstrate that Cu(II) complexes are effective as fluorescent probes for detecting NO in both organic and aqueous environments.     

4,5-二氮芴-9-酮Cu(II),Zn(II)配合物的合成、晶体结构、热分析及理论计算

合成了 4,5 二氮芴 9 酮 (dafo)的Cu(II) ,Zn(II)配合物 [Cu(dafo) 2 (H2 O) 2 ] (NO3 ) 2 和 [Zn(dafo) 2 (H2 O) 2 ] (NO3 ) 2 ,通过单晶X射线衍射法确定了它们的结构 .晶体结构分析表明 ,配合物分子中Cu(II) ,Zn(II)分别和来自两配体的四个氮原子及两个水分子中的氧原子配位 ,处于六配位的配位环境中 ,两配体基本处于同一平面 ,两水分子垂直于两配体所在平面 ,Cu(II)处于畸变八面体中心 ,Zn(II)处于正常八面体中心 ,对两种配合物进行了元素分析、红外和热分析表征 ,在实验的基础上 ,采用Gaussian 98w中的DFT B3LYP/LANL2DZ对两种配合物进行了全几何优化以及后续计算     

A series of trinuclear Cu(II)Ln(III)Cu(II) complexes derived from 2,6-Di(acetoacetyl)pyridine: synthesis, structure, and magnetism

A series of trinuclear Cu(II)Ln(III)Cu(II) complexes with the bridging ligand 2,6-di(acetoacetyl)pyridine have been prepared by one-pot reaction with Cu(NO(3))(2).3H(2)O and Ln(NO(3))(3).nH(2)O in methanol. X-ray crystallographic studies for all the complexes indicate that two L(2)(-) ligands selectively sandwich two Cu(II) ions with the 1,3-diketonate entities and one Ln(III) ion with the 2,6-acetylpyridine entity to form a trinuclear CuLnCu core bridged by the enolate oxygen atoms. Cryomagnetic properties of the complexes are studied with respect to the electronic structure of the Ln ion.     

Redox-driven intramolecular anion translocation between a metal centre and a hydrogen-bond-donating compartment

Dicationic ligands incorporating two 2,2'-bipyridine units and two imidazolium moieties, [1](2+) and [2](2+), form stable chelate complexes with Cu(II) and Cu(I) in acetonitrile solution. Each Cu(II) complex binds two X(-) ions according to two stepwise equilibria, the first involving the Cu(II) centre and the second involving the bis-imidazolium compartment. Cu(I) complexes are able to host only one NO(3)(-) ion in the bis-imidazolium cavity, while other anions induce demetallation. Thus, in the presence of one equivalent of NO(3)(-), the Cu(II)/Cu(I) redox change makes the anion translocate quickly and reversibly from one binding site to the other within the [Cu(II,I)(1)](4+/3+) system, as demonstrated by cyclic voltammetry and controlled-potential electrolysis experiments.     

Pyridazine- versus pyridine-based tridentate ligands in first-row transition metal complexes

A series of first-row transition metal complexes with the unsymmetrically disubstituted pyridazine ligand picolinaldehyde (6-chloro-3-pyridazinyl)hydrazone (PIPYH), featuring an easily abstractable proton in the backbone, was prepared. Ligand design was inspired by literature-known picolinaldehyde 2-pyridylhydrazone (PAPYH). Reaction of PIPYH with divalent nickel, copper, and zinc nitrates in ethanol led to complexes of the type [Cu(II)(PIPYH)(NO(3))(2)] (1) or [M(PIPYH)(2)](NO(3))(2) [M = Ni(II) (2) or Zn(II) (3)]. Complex synthesis in the presence of triethylamine yielded fully- or semideprotonated complexes [Cu(II)(PIPY)(NO(3))] (4), [Ni(II)(PIPYH)(PIPY)](NO(3)) (5), and [Zn(II)(PIPY)(2)] (6), respectively. Cobalt(II) nitrate is quantitatively oxidized under the reaction conditions to [Co(III)(PIPY)(2)](NO(3)) (7) in both neutral and basic media. X-ray diffraction analyses reveal a penta- (1) or hexa-coordinated (2, 3, and 7) metal center surrounded by one or two tridentate ligands and, eventually, κ-O,O' nitrate ions. The solid-state stoichiometry was confirmed by electron impact (EI) and electrospray ionization (ESI) mass spectrometry. The diamagnetic complexes 5 and 6 were subjected to (1)H NMR spectroscopy, suggesting that the ligand to metal ratio remains constant in solution. Electronic properties were analyzed by means of cyclic voltammetry and, in case of copper complexes 1 and 4, also by electron paramagnetic resonance (EPR) spectroscopy, showing increased symmetry upon deprotonation for the latter, which is in accordance with the proposed stoichiometry [Cu(II)(PIPY)(NO(3))]. Protic behavior of the nickel complexes 2 and 5 was investigated by UV/vis spectroscopy, revealing high π-backbonding ability of the PIPYH ligand resulting in an unexpected low acidity of the hydrazone proton in nickel complex 2.     

Synthesis and structure of metal complexes containing zwitterionic N-hydroxyimidazole ligands

Cu(II) and Zn(II) complexes of N-hydroxyimidazoles were synthesised by reacting simple metal perchlorate salts with the imidazole ligand in alcohol and formulated with a metal:ligand ratio of 1:2. The X-ray crystal structures of five complexes (four Cu(II) and one Zn(II)) were obtained and each showed the two trans, N-hydroxyimidazole ligands forming six-membered, chelate rings with the metal. Both of the NO chelating, neutral N-hydroxyimidazole ligands are in the zwitterion form, with the uncoordinated imidazole imine N atom being protonated and the oxime O atom deprotonated. In the solid state the complexes form hydrogen-bonded supramolecular structures.     

Direct nitric oxide detection in aqueous solution by copper(II) fluorescein complexes

A series of FL(n) (n = 1-5) ligands, where FL(n) is a fluorescein modified with a functionalized 8-aminoquinoline group as a copper-binding moiety, were synthesized, and the chemical and photophysical properties of the free ligands and their copper complexes were investigated. UV-visible spectroscopy revealed a 1:1 binding stoichiometry for the Cu(II) complexes of FL(1), FL(3), and FL(5) in pH 7.0 buffered aqueous solutions. The reactions of FL(2) or FL(4) with CuCl(2), however, appear to produce a mixture of 1:1 and 1:2 complexes, as suggested by Job's plots. These binding modes were modeled by the synthesis and X-ray crystal structure determination of Cu(II) complexes of 2-[(quinolin-8-ylamino)methyl]phenol (modL), employed as a surrogate of the FL(n) ligand family. Two kinds of crystals, [Cu(modL)(2)](BF(4))(2) and [Cu(2)(modL')(2)(CH(3)OH)](BF(4))(2) (modL' = 2-[(quinolin-8-ylamino)methyl]phenolate), were obtained. The structures suggest that one oxygen and two nitrogen atoms of the FL(n) ligands most likely bind to Cu(II). Introduction of nitric oxide (NO) to pH 7.0 buffered aqueous solutions of Cu(FL(n)) (1 microM CuCl(2) and 1 microM FL(n)) at 37 degrees C induces an increase in fluorescence. The fluorescence response of Cu(FL(n)) to NO is direct and specific, which is a significant improvement over commercially available small molecule-based probes that are capable of detecting NO only indirectly. The NO-triggered fluorescence increase of Cu(FL(5)) occurs by reduction of Cu(II) to Cu(I) with concomitant dissociation of the N-nitrosated fluorophore ligand from copper. Spectroscopic and product analyses of the reaction of the FL(5) copper complex with NO indicated that the N-nitrosated fluorescein ligand (FL(5)-NO) is the species responsible for fluorescence turn-on. Density functional theory (DFT) calculations of FL(5) versus FL(5)-NO reveal how N-nitrosation of the fluorophore ligand brings about the fluorescence increase. The copper-based probes described in the present work form the basis for real-time detection of nitric oxide production in living cells.     

Trinuclear copper complexes with triplesalen ligands: geometric and electronic effects on ferromagnetic coupling via the spin-polarization mechanism

A series of trinuclear Cu(II) complexes with the tris(tetradentate) triplesalen ligands H(6)talen, H(6)talen(tBu(2) ), and H(6)talen(NO(2) ), namely [(talen)Cu(II) (3)] (1), [(talen(tBu(2) ))Cu(II) (3)] (2), and [(talen(NO(2) ))Cu(II) (3)] (3), were synthesized and their molecular and electronic structures determined. These triplesalen ligands provide three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone. The structure of [(talen)Cu(II) (3)] (1) was communicated recently. The structure of the tert-butyl derivative [(talen(tBu(2) ))Cu(II) (3)] (2) was established in three different solvates. The molecular structures of these trinuclear complexes show notable differences, the most important of which is the degree of ligand folding around the central Cu(II)-phenolate bonds. This folding is symmetric with regard to the central phloroglucinol backbone in two structures, where it gives rise to bowl-shaped overall geometries. For one solvate two trinuclear triplesalen complexes form a supramolecular disk-like arrangement, hosting two dichloromethane molecules like two pearls in an oyster. The FTIR spectra of these complexes indicate the higher effective nuclear charge of Cu(II) in comparison to the trinuclear Ni(II) complexes by the lower C--O and higher C=N stretching frequencies. The UV/Vis/NIR spectra of 1-3 reflect the stronger ligand folding in the tert-butyl complex 2 by an intense phenolate-to-Cu(II) LMCT. This absorption is absent in 1 and is obscured by the nitro chromophore in 3. The more planar molecular structures cause orthogonality of the Cu(II) d(x(2)-y(2) ) orbital and the phenolate O p(z) orbital, which leads to small LMCT dipole strengths. Whereas 1 and 3 exhibit only irreversible oxidations, 2 exhibits a reversible one-electron oxidation at +0.26 V, a reversible two-electron oxidation at +0.59 V, and a reversible one-electron oxidation at +0.81 V versus Fc(+)/Fc. The one-electron oxidized form 2(+) is strongly stabilized with respect to reference mononuclear salen-like Cu complexes. Chemical one-electron oxidation of 2 to 2(+) allows the determination of its UV/Vis/NIR spectrum, which indicates a ligand-centered oxidation that can be assigned to the central phloroglucinol unit by analogy with the trinuclear Ni triplesalen series. Delocalization of this oxidation over three Cu(II)-phenolate subunits causes the observed energetic stabilization of 2(+). Temperature-dependent magnetic susceptibility measurements reveal ferromagnetic couplings for all three trinuclear Cu(II) triplesalen complexes. The trend of the coupling constants can be rationalized by two opposing effects: 1) electron-withdrawing terminal substituents stabilize the central Cu(II)-phenolate bond, which results in a stronger coupling, and 2) ligand folding around the central Cu(II)-phenolate bond opens a bonding pathway between the magnetic Cu(II) d(x(2)-y(2) ) orbital and the phenolate O p(z) orbital, which results in a stronger coupling. Density functional calculations indicate that both spin-polarization and spin-delocalization are operative and that slight geometric variations alter their relative magnitudes.     

Comparative study of C(2) epimerization of d-glucose and d-mannose catalyzed by water soluble organometallic complexes with nitrogen ligands

Epimerization of d-glucose and d-mannose, catalyzed by the water soluble complexes of Cu(II), Ni(II), Co(II) and Cd(II) with bisnitrogen ligands 4–7, and by Mo(VI) complexes prepared in situ from ammonium heptamolybdate (AHM) with ligands 4–9 is compared. All examined complexes exhibit lower catalytic activity than AHM: strong coordination of the ligands by both (N,O) heteroatoms to metal ions, presumably affords catalytically less active species. Some free ligands and their metal (II) complexes catalyze both C(2) epimerization and isomerization of aldoses to d-fructose.     

Galactose oxidase models: solution chemistry, and phenoxyl radical generation mediated by the copper status

Galactose oxidase (GO) is an enzyme that catalyzes two-electron oxidations. Its active site contains a copper atom coordinated to a tyrosyl radical, the biogenesis of which requires copper and dioxygen. We have recently studied the properties of electrochemically generated mononuclear Cu(II)-phenoxyl radical systems as model compounds of GO. We present here the solution chemistry of these ligands under various copper and dioxygen statuses: N(3)O ligands first chelate Cu(II), leading, in the presence of base, to [Cu(II)(ligand)(CH(3)CN)](+) complexes (ortho-tert-butylated ligands) or [(Cu(II))(2)(ligand)(2)](2+) complexes (ortho-methoxylated ligands). Excess copper(II) then oxidizes the complex to the corresponding mononuclear Cu(II)-phenoxyl radical species. N(2)O(2) tripodal ligands, in the presence of copper(II), afford directly a copper(II)-phenoxyl radical species. Addition of more than two molar equivalents of copper(II) affords a Cu(II)-bis(phenoxyl) diradical species. The donor set of the ligand directs the reaction towards comproportionation for ligands possessing an N(3)O donor set, while disproportionation is observed for ligands possessing an N(2)O(2) donor set. These results are discussed in the light of recent results concerning the self-processing of GO. A path involving copper(II) disproportionation is proposed for oxidation of the cross-linked tyrosinate of GO, supporting the fact that both copper(I) and copper(II) activate the enzyme.     

Comparative study of C(2) epimerization of -glucose and -mannose catalyzed by water soluble organometallic complexes with nitrogen ligands

Epimerization of -glucose and -mannose, catalyzed by the water soluble complexes of Cu(II), Ni(II), Co(II) and Cd(II) with bisnitrogen ligands 4–7, and by Mo(VI) complexes prepared in situ from ammonium heptamolybdate (AHM) with ligands 4–9 is compared. All examined complexes exhibit lower catalytic activity than AHM: strong coordination of the ligands by both (N,O) heteroatoms to metal ions, presumably affords catalytically less active species. Some free ligands and their metal (II) complexes catalyze both C(2) epimerization and isomerization of aldoses to -fructose.     

Nitric oxide reduction of copper(II) complexes: spectroscopic evidence of copper(II)-nitrosyl intermediate

Two copper(II) complexes, 1 and 2 with L(1) and L(2) [L(1) = 2- aminomethyl pyridine; L(2) = bis-(2-aminoethyl)amine], respectively, in degassed acetonitrile solvent, on exposure to NO gas, were found to form a thermally unstable [Cu(II)-NO] intermediate which then resulted in the reduction of the copper(II) centers. The formation of the [Cu(II)-NO] intermediate was evidenced by UV-visible, FT-IR, and EPR spectroscopic studies. The reduction of the copper(II) centers by nitric oxide afforded ligand transformation through diazotization at the primary amine coordination site, in both cases. The modified ligands, in each case, were isolated and characterized.     

Design and spectroscopic characterization of peptide models for the plastocyanin copper-binding loop

The Cu(II)- and Co(II)-binding properties of two peptides, designed on the basis of the active site sequence and structure of the blue copper protein plastocyanin, are explored. Peptide BCP-A, Ac-Trp-(Gly)(3)-Ser-Tyr-Cys-Ser-Pro-His-Gln-Gly-Ala-Gly-Met-(Gly )(3)-His-(Gly)(2)-Lys-CONH(2), conserves the Cu-binding loop of plastocyanin containing three of the four copper ligands and has a flexible (Gly)(3) linker to the second His ligand. Peptide BCP-B, Ac-Trp-(Gly)(3)-Cys-Gly-His-Gly-Val-Pro-Ser-His-Gly-Met-Gly-CONH(2), contains all four blue copper ligands, with two on either side of a beta-turn. Both peptides form 1:1 complexes with Cu(II) through His and Cys ligands. BCP-A, the ligand loop, binds to Cu(II) in a tetrahedrally distorted square plane with axial solvent ligation, while BCP-B-Cu(II) has no tetrahedral distortion in aqueous solution. In methanolic solution, distortion of the square plane is evident for both BCP-Cu(II) complexes. Tetrahedral Co(II) complexes are observed for both peptides in aqueous solution but with 4:2 peptide:Co(II) stoichiometries as estimated by ultracentrifugation. Cu(II) reduction potentials for the aqueous peptide-Cu(II) complexes were measured to be +75 +/- 30 mV vs NHE for BCP-A-Cu(II) and -10 +/- 20 mV vs NHE for BCP-B-Cu(II). The results indicate that the plastocyanin ligand loop can act as a metal-binding site with His and Cys ligands in the absence of the remainder of the folded protein but, by itself, cannot stabilize a type 1 copper site, emphasizing the role of the protein matrix in protecting the Cu binding site from solvent exposure and the Cys from oxidation.     

Coordination compounds of biological interest: thermal properties of some compounds of saccharin (o-benzoic sulfimide) with divalent metal ions

The thermal properties of cobalt(II) and copper(II) complexes of saccharin (sacc) (o-benzoic sulfimide) have been studied, and are compared with those of ternary complexes of cobalt(II) and copper(II) having both saccharin and pyridine as ligands. The thermal behaviour is discussed in terms of the bonds between the central ion and the ligands. The frequency shifts of the carbonyl and sulfonyl groups support the hypotheses derived from the thermal data. The thermal stability scale CO(II) /s> Cu(II) is always obtained while the stability constant scale is CO(II) < Cu(II).     

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).     

Trinuclear, tetranuclear, and polymeric Cu(II) complexes from the first use of 2-pyridylcyanoxime in transition metal chemistry: synthetic, structural, and magnetic studies

The first use of 2-pyridylcyanoxime, (py)C(CN)NOH, in transition metal chemistry is described. Depending on the nature of the metal starting material and the reaction conditions employed, the Cu(II)/(py)C(CN)NOH system has provided access to complexes [Cu(3)O{(py)C(CN)NO}(3)(NO(3))(H(2)O)(2)(MeOH)] (1), [Cu(4)O{(py)C(CN)NO}(4)(O(2)CMe)(2)] (2), [Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)](2n)·n[Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)] (3), and [Cu{(py)C(CN)NO}(2)](n) (4). The molecule of 1 consists of three Cu(II) atoms in a strictly equilateral arrangement bridged by a central μ(3)-oxide group. The molecule of 2 consists of a tetrahedron of Cu(II) atoms held together by a central μ(4)-oxide ion, four η(1):η(1):η(1):μ-(py)C(CN)NO(-) ligands and two η(1):η(1):μ-MeCO(2)(-) groups. The crystal structure of 3 consists of [Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)](2n) double chains and discrete cluster [Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)] molecules. The crystal structure of 4 consists of neutral polymeric chains based on centrosymmetric mononuclear [Cu{(py)C(CN)NO}(2)] units. The Cu(II) atoms are doubly bridged by the oximate groups of two η(1):η(1):η(1):μ-(py)C(CN)NO(-) ligands. Variable-temperature, solid-state direct current (dc) magnetic susceptibility studies were carried out for 1-4. The data indicate very strong antiferromagnetic exchange interactions for 1-3. The obtained J values are discussed in depth on the basis of the structural parameters of the complexes, literature reports, and existing magnetostructural correlations.     

Copper(II) complexes of N-octylated bis(benzimidazole) diamide ligands and their peroxide-dependent oxidation of aryl alcohols

New N-octylated benzimidazole-based diamide ligands N,N'-bis(N-octylbenzimidazolyl-2-ethyl)hexanediamide (O-ABHA), possessing a chiral center, and N,N'-bis(N-octylbenzimidazolyl-2-methyl)hexanediamide (O-GBHA) have been synthesized and utilized to prepare Cu(II) complexes of general composition [Cu(L)X]X, where L = O-ABHA or O-GBHA and X = Cl(-) or NO(3)(-) . The X-ray structure of one of the complexes, [Cu(O-GBHA)NO(3)]NO(3), has been obtained. The Cu(II) ion is found to possess a distorted octahedral geometry with a highly unsymmetrical bidentate nitrate group. The N(2)O(2) equatorial plane comprises an amide carbonyl O, a nitrate O, and the two benzimidazole imine N atoms while another amide carbonyl O and nitrate O take up the axial positions. The complexes carry out the oxidation of aromatic alcohols to aldehydes in the presence of cumenyl hydroperoxide at 40-45 degrees C and act as catalyst with turnovers varying between 13- and 27-fold. The percentage yields of the respective products have been obtained which vary from 32% to 65% with respect to the catalyst turnover.     

Controlled aggregation of heterometallic nanoscale Cu12Ln6 clusters (Ln = Gd(III) or Nd(III)) into 2D coordination polymers

Discrete dinuclear and polymeric heterometallic copper(II)-lanthanide(III) complexes have been synthesized upon variation of pH and characterized by X-ray diffraction analysis. Reactions of the ligand Htza (tetrazole-1-acetic acid) with copper(II) and lanthanide(III) salts gave dinuclear [CuLn(tza)4(H2O)5Cl] complexes at the low pH of 3.5 and 2D heterometallic coordination polymers with high-nuclearity [{Cu2(OH)2}2{Cu12Ln6(mu3-OH)24(Cl)(1/2)(NO3)(1/2)(tza)12(H2O)18}](NO3)(9).8H2O (Ln = Gd or Nd) at a higher pH of 6.6. The acidity of the reaction solution can cause drastic changes in the structures of the products. In the dinuclear complexes, each pair of adjacent dinuclear molecules is linked through hydrogen bonds and pi-pi stacking interactions, and the whole structure is a hydrogen-bonded three-dimensional cubic net. In the coordination polymers, the connecting nodes are [Cu12Ln6] units, which are interconnected by [Cu2O2] units into two-dimensional structures. Magnetic studies exhibit the existence of weak exchange interactions between the Cu(II) and Ln(III) ions bridged by carboxylate and hydroxy ligands.     

EPR of Cu(II)-doped seven-coordinate inclusion compounds, M(stpy)3(NO3)2 x 1/2stpy (M = Cd(II) and Zn(II), stpy = trans-4-styrylpyridine): low symmetry effects in admixture of ground states

Single crystal EPR of Cu(II)-doped low symmetry pentagonal bipyramidal Werner-type clathrate inclusion complexes of Cd(stpy)3(NO3)2 x 1/2stpy(1) and Zn(stpy)3(NO3)2 x 1/2stpy(2) (stpy = trans-4-styrylpyridine) is reported. The spin Hamiltonian parameters are found to be orthorhombic with g33 = 2.298, g22 = 2.108, g11 = 2.066, A33 = 107.3, A22 = 54.4 and A11 = 23.1 x 10(-4) cm(-1) for 1 and g33 = 2.292, g22 = 2.111, g11 = 2.067, A33 = 107.5, A22 = 54.7 and A11 = 22.9 x 10(-4) cm(-1) for 2. Angular variation studies for both 1 and 2 suggest that the Cu(II) ions are substitutionally incorporated in the host lattices. The magnitude of Cu(II) hyperfine coupling constant (A33) in both 1 and 2 are found to be low, in comparison to those of the pure Cu(II) complex, indicative of low symmetry for the substitutional sites in accordance with the crystal data. Such large reductions in Cu(II) hyperfine coupling are explicable in terms of a mixed d(x2 - y2)/dz2 ground state and delocalization of unpaired spin density onto the ligands.     

Synthesis, electronic and ESR spectral studies on copper(II) nitrate complexes with some acylhydrazines and hydrazones

This paper describes the preparation of [Cu(bh)(2)(H(2)O)(2)](NO(3))(2)], [Cu(ibh)(2)(NO(3))(2)], [Cu(ibh)(2)(H(2)O)(2)](NO(3))(2) and [Cu(iinh)(2)(NO(3))(2)] (bh=benzoyl hydrazine (C(6)H(5)CONHNH(2)); ibh=isonicotinoyl hydrazine (NC(5)H(4)CONHNH(2)); ibh=isopropanone benzoyl hydrazone (C(6)H(5)CONHN=C(CH(3))(2); iinh=isopropanone isonicotinoyl hydrazone (NC(5)H(4)CONHN=C(CH(3))(2)). These copper(II) complexes are characterized by elemental analyses, molar conductances, dehydration studies, ESR, IR and electronic spectral studies. The electronic and ESR spectra indicate that each complex exhibits a six-coordinate tetragonally distorted octahedral geometry in the solid state and in DMSO solution. The ESR spectra of most of the complexes are typically isotropic type at room temperature (300K) in solid state as well as in DMSO solution. However, all the complexes exhibit invariably axial signals at 77K in DMSO solution. The trend g(||)>g( perpendicular)>g(e,) observed in all the complexes suggests the presence of an unpaired electron in the [Formula: see text] orbital of the Cu(II). The bh and inh ligands bond to Cu(II) through the >CO and NH(2) groups whereas, ibh and iinh bond through >CO and >CN groups. The IR spectra of bh and ibh complexes also show HOH stretching and bending modes of coordinated water.