Synthesis,crystal structure and magnetic properties of a new macrocyclic trinuclear CuII-CuII-CuII complex

A new oxamido-bridged trinuclear copper(II) complex [(CuL)₂Cu](ClO₄)₂·0.5H₂O (L?=?the dianion of 2,3-dioxo-5,6,14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclotetradeca-7,12-diene) has been synthesized by self-assembly and characterized. X-ray diffraction analysis reveals that the title complex is monoclinic, space group P2₁, with a?=?16.213(5), b?=?9.811(3), c?=?18.802(6)?Å, β?=?96.790(5)°. The central copper(II) ion lies in a distorted octahedral environment. Terminal coppers have square pyramidal coordination geometry. Magnetic measurements show there is strong antiferromagnetic interaction between the central and the terminal Cu(II) ions.     

Synthesis,crystal structure,spectroscopy and magnetism of a trinuclear nickel(II) complex with 3,5-pyrazoledicarboxylic acid as bridge ligands

A new complex of [Ni₃(dcp)₂(H₂O)₁₀] (1) (H₃dcp = 3,5-pyrazoledicarboxylic acid) has been synthesized from H₃dcp and Ni(NO₃)₂·6H₂O by hydrothermal reaction. Complex 1 has the discrete trinuclear structure. Three Ni(II) ions are bridged by two dcp³⁻ ligands, with 10 coordinated water molecules as terminal ligands. The molecules of [Ni₃(dcp)₂(H₂O)₁₀] extend into three-dimensional supramolecular architectures by intermolecular O–H···O hydrogen bonds as well as π-π stacking interactions. Magnetic susceptibility measurement shows that a weak antiferromagnetic interaction is operative between nickel(II) ions and an excellent simulation of the experimental data gives D = 5.27 cm⁻¹, J = −2.19 cm⁻¹ and g = 2.05.     

Synthesis and study of trinuclear Pd(II) and Pt(II) complexes with 2-mercaptonicotinic acid: Crystal and molecular structure of [Pd3(mercaptonicotinic acid)3Cl3]

Pd(II) and Pt(II) complexes of 2-mercaptonicotinic acid of formulae [M₃(mercaptonicotinic acid)₃Cl₃] were synthesized and characterized by the usual spectroscopic techniques including mass spectrometry. The crystal structure was obtained for the palladium complex. The molecule has a ternary symmetry, and mercaptonicotinic acid coordinates in a bidentate (N,S) mode to each palladium ion. The sulfur atom acts as a bridge between two palladium atoms. The fourth coordination site in the plane square geometry of the Pd(II) is occupied by a chloride ion. Identical molecular structure is proposed for the platinum compound in agreement with the spectroscopic and theoretical results.     

A novel triply bridged dinuclear four-coordinate copper(I) complex with sterically bulky bis(dicyclohexylphosphino)methane ligand

A novel triply bridged dinuclear copper(I) complex: Cu₂(μ-paa)(μ-dcpm)₂(BF₄)₂·2CH₂Cl₂ [ paa = pyridine-2-carbaldehyde azine (C₁₂H₁₀N₄) and dcpm = bis(dicyclohexylphosphino)methane(C₂₅H₄₆P₂) ] has been synthesized and structurally characterized. Crystallographic studies of the complex showed that two copper(I) ions were bridged by one paa ligand and two dcpm ligands. The paa ligand adopted the Z configuration at the partially double N-N bond and the two copper ions have distorted tetrahedral coordination geometry. Because of the steric effect of dcpm, the pyridine rings of the paa ligand are obviously not on the same plane (the dihedral angle is 43.61⁰). The interaction between neighboring ligands results in a N-N bond length (1.374(7) Å) contraction. The UV-vis spectra of the complex exhibited intense high-energy absorptions at λ_max < 340 nm and broad visible bands in a range of 380?550 nm, ascribed to intraligand (IL π-π*) transitions and metal-to-ligand charge-transfer (MLCT) transitions, respectively. Interestingly, the absorbtion peaks varied regularly with the solvent polarity. Although the complex has a rigid structure with the copper ions held firmly by triply bridged ligands, the emission and excitation spectra revealed that the complex exhibits weak fluorescence.

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Structural and photophysical studies on a linear trinuclear zinc complex of 2-[(2-hydroxyethylimino)methyl]quinolin-8-ol

A linear trinuclear zinc complex was obtained when after refluxing 8-hydroxyquinoline-2-carboxaldehyde and 2-aminoethanol (in a 1:1 molar ratio) until the formation of the H₂L ligand, a methanol solution of zinc acetate dihydrate was added. Reaction between Zn(OAc)₂·2H₂O and H₂L, both in 3:2 or 4:2 ratios, yielded Zn₃(HL)₂(OAc)₄. This latter could be crystallographically characterised, and rather surprisingly, the potentially tetradentate HL⁻ is only acting as an O,N-donor, while two phenolate and four acetate bridges hold together the three zinc ions. A study of the luminescence properties in methanol solution showed that the quantum yield of Zn₃(HL)₂(OAc)₄ (Φ_F = 0.07) is slightly higher than that of 8-hydroxyquinoline-2-carboxaldehyde (Φ_F = 0.06).     

Synthesis and Magnetic Properties of Novel Azamacrocyclic LnIII,CuII, FeIII,and SrII Complexes and Conformational Analysis of the Ligands

Hexaalkoxy‐substituted azamacrocyclic metal complexes 1 · MX_n [MX_n = FeCl₃, CuCl₂, SrCl₂, Ln(NO₃)₃; Ln = La, Pr, Eu, Ho, Er] with various chain lengths were prepared by a convergent approach using 1,2‐bisalkoxy‐4,5‐diamines 3 and 4‐alkoxy‐pyridine‐2,6‐dicarbaldehydes 4 as key building blocks for template‐assisted cyclocondensation. Metal complexes 1 · MX_n were considered as potential metallomesogens. However, differential scanning calorimetry and optical polarizing microscopy of 1 · MX_n did not reveal any mesomorphism. The magnetic susceptibility shows deviation from Curie‐like behavior. Due to ligand field effects the effective magnetic moments are a function of the temperature. In order to obtain structural informations on the free ligand 1 , which is synthetically not accessible, theoretical calculations were carried out. For the free azamacrocycle 2a and the free hexamethoxy‐substituted azamacrocycle 1a the IR spectra were computed at the level of density functional theory. A planar and a saddle‐shaped conformation was considered. The IR spectra and especially the dependence of the C=N vibration on the structural parameters and the charge distribution are discussed.     

Synthesis, crystal structure, and magnetic properties of a cobalt(II) complex with (3,5-dichloropyridin-4-yl)(pyridin-4-yl)methanol

A novel bridging ligand, (3,5-dichloropyridin-4-yl)(pyridin-4-yl)methanol (I), and its cobalt(II) complex, [Co(I)₂(NCS)₂]_n (II), were prepared. The structures of ligand I and complex II were determined by single crystal X-ray analysis. Magnetic susceptibility measurements were performed for cobalt (II) complex II. Compound I crystallised in orthorhombic space group Pbca with a = 7.6585(14) Å, b = 12.209(2) Å, c = 23.207(4) Å, V= 2170.0(7) ų and Z=8. Complex II crystallised in monoclinic space group P2₁/n with a = 13.223(8) Å, b = 16.959(10) Å, c = 13.948(8) Å, β = 115.395(10)°, V= 2826(3) ų and Z = 4. Each cobalt(II) ion is surrounded by two NCS^? anions and four pyridyl moieties from two bridging ligands. Each bridging ligand connects two neighbouring Co(II) ions to form a 2-dimensional structure. Temperature dependence of the molar magnetic susceptibilities in the temperature range of 2–300 K revealed that magnetic interactions between the cobalt ions are weak.     

Magneto-Structural Correlations in Trinuclear Cu(II) Complexes: A Density Functional Study

Summary.  Density functional theoretical methods have been used to study magneto-structural correlations for linear trinuclear hydroxo-bridged copper(II) complexes. The nearest-neighbor exchange coupling constant shows very similar trends to those found earlier for dinuclear compounds for which the Cu–O–Cu angle and the out of plane displacement of the hydrogen atoms at the bridge are the two key structural factors that determine the nature of their magnetic behavior. Changes in these two parameters can induce variations of over 1000 cm⁻¹ in the value of the nearest-neighbor coupling constant. On the contrary, coupling between next-nearest neighbors is found to be practically independent of structural changes with a value for the coupling constant of about −60 cm⁻¹. The magnitude calculated for this coupling constant indicates that considering its value to be negligible, as usually done in experimental studies, can lead to considerable errors, especially for compounds in which the nearest-neighbor coupling constant is of the same order of magnitude. Corresponding author. E-mail: eliseo.ruiz@qi.ub.es Received June 28, 2002; accepted July 22, 2002     

A linear S-bridged trinuclear cobalt(III) complex with 2-aminobenzenethiol: synthesis,crystal structure,and spectroscopic characterization

Treatment of cobalt(II) perchlorate hexahydrate with 2?M equiv. of 2-aminobenzenethiol (Habt) in acetonitrile afforded a tricationic tricobalt complex, [Co{Co(abt)₃}₂](ClO₄)₃·2CH₃CN, by aerial oxidation. The molecular structure of the meso (ΔΛ) form of the complex was determined by X-ray crystallography. In the complex cation, the central Co is coordinated by six thiolate groups from two terminal fac(S)-[Co(abt)₃] units in an octahedral geometry, forming a linear S-bridged tricobalt structure.     

Magnetic characterization, synthesis and crystal structure of a heterodinuclear CuGd Schiff base complex bridged by the two phenolic oxygen atoms

A novel heterodinuclear complex formed by the reaction of gadolinium nitrate with Schiff base complex of copper(II) has been synthesized and characterized. Preparation, crystal structure and magnetic properties of the heterodinuclear complex, LCu(Me₂CO)Gd(NO₃)₃, (L=(N,N′-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane) are reported. The complex is consisting of a deca-coordinated Gd^III ion which is bridged to four coordinated Cu^II via both phenolate oxygen atoms of the L Schiff base ligand. The average CuGd separation is 3.475(2) Å. There is also one non-coordinating acetone molecule in the crystal structure. The magnetic susceptibility of the complex was measured over the range 4.5–350 K and the observed data were successfully simulated by the equation based on the spin-Hamiltonian operator H=−JS_Cu·S_Gd. The values of the intrachain interaction parameters have been deduced from the magnetic data: exchange integral J(Cu–Gd)=7.3 cm⁻¹, g_Cu=2.17, g_Gd=2.09. This indicates a weak ferromagnetic spin exchange interaction between Cu^II and Gd^III ions. The nature of the magnetic super-exchange interaction of the title compound is compared with similar Cu^IIGd^III heterodinuclear complexes.     

Localized Orbitals vs. Pseudopotential-Plane Waves Basis Sets: Performances and Accuracy for Molecular Magnetic Systems

 Density functional theory, in combination with a) a careful choice of the exchange-correlation part of the total energy and b) localized basis sets for the electronic orbitals, has become the method of choice for calculating the exchange-couplings in magnetic molecular complexes. Orbital expansion on plane waves can be seen as an alternative basis set especially suited to allow optimization of newly synthesized materials of unknown geometries. However, little is known on the predictive power of this scheme to yield quantitative values for exchange coupling constants J as small as a few hundredths of eV (50–300 cm⁻¹). We have used density functional theory and a plane waves basis set to calculate the exchange couplings J of three homodinuclear Cu-based molecular complexes with experimental values ranging from +40 cm⁻¹ to −300 cm⁻¹. The plane waves basis set proves as accurate as the localized basis set, thereby suggesting that this approach can be reliably employed to predict and rationalize the magnetic properties of molecular-based materials. Corresponding author. E-mail: Carlo.Massobrio@ipcms.u-strasbg.fr Received August 5, 2002; accepted August 9, 2002     

Phthalocyanoiron complex with bridged ligands. Electronic structure of monomers and polymers

Electronic structure aspects related to the semiconducting properties of monomers and polymers of phthalocyanoiron with bidentate bridging ligands, PcFe–L₂ and ? [PcFe(L)]_n, have been investigated from density functional calculations [L = pyrazine, triazine, tetrazine, pyridine, 4,4′‐bipyridine, bipyridyacetylene, and bis(4‐pyridyl)bencene]. The following relevant results have been obtained: (a) an energy analysis in terms of electrostatic interaction, Pauli repulsion, and occupied/virtual orbital interactions show that the Pauli repulsion is the origin that the axial ligands (L) prefer be located toward the aza positions of the macrocycle, and (b) the intrinsic semiconducting properties depend of the frontier band. The valence band is composed largely by the transition metal d_xy orbital. The conduction band is composed of a mixture between the metallomacrocycle and bridged ligand orbitals for systems formed by pyrazine, bipyridine, and bipyridyacetylene. However, this composition is different when the ligands are triazine and tetrazine, which show a band composed of π* orbitals. These systems are predicted to show the higher conductivity within the series, in agreement with experimental results. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 170–181, 2001     

Fe/Cr超晶格的电子结构和磁性质

应用密度泛函全势线性缀加平面波(FLAPW)方法研究了Fem/Crn (m=3, 4; n=1, 3, 4)超晶格的电子结构和磁性质. 结果表明, Fe3/Cr1和Fe3/Cr3体系的基态中, Fe层间存在铁磁耦合; 而Fe4/Cr4体系基态中, 存在反铁磁耦合; Cr层的磁矩方向交替变化, 交界面上的Fe和Cr间存在反铁磁耦合.     

Synthesis, crystal structure and DFT analysis of a new trinuclear complex of copper

The new trinuclear complex [Cu₂(μ-L)₂CuCl₂] has been synthesized and characterized by elemental analysis, IR, UV-Vis and X-ray spectroscopy, where L is a dianionic tetradentate Schiff base ligand with N₂O₂ donor atoms. The molecular structure of [Cu₂(μ-L)₂CuCl₂] was determined by X-ray crystallography. In the complex, the most remarkable aspect of the trinuclear complex is that it adopts a bent structure for the three copper atoms, with a Cu1Cu3Cu2 intramolecular angle of approximately 90.62(2)°. All three copper atoms are five coordinate, with a slightly distorted square pyramidal geometry. In the two terminals moieties, the basal plane of the square pyramidal is formed by two oxygen atoms and two nitrogen atoms of the Schiff base ligand, and the apical position at the Cu atom is occupied by the bridging Cl1 anion. The Cu1Cl1Cu2 angle is 110.51(5)°. The central copper atom also has a five-coordinate, slightly distorted square pyramidal geometry, with four phenolato oxygens belonging to the Schiff base ligands from Cu(salpn) units describing the square planar base and the Cl anions being apical. The optimized structure of the complex has been studied using the B3LYP/6-31G(d)/LanL2TZf level of theory. The calculation shows that all the copper atoms are five coordinate with distorted square pyramidal structures, which is consistent with experimental data.     

Synthesis,crystal structure,and magnetic properties of a linear trinuclear Cu(II) complex

A new linear trinuclear Cu(II) complex, [Cu₃(NTA)₂(4,4′-bpt)₄(H₂O)₂]?·?10H₂O (H₃NTA?=?nitrilotriacetic acid, 4,4′-bpt?=?4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole) (1), was obtained from evaporation of an aqueous solution containing Cu(NO₃)₂?·?6H₂O, 4,4′-bpt, nitrilotriacetic acid (H₃NTA), and NaOH. 1 was characterized using single-crystal X-ray diffraction, IR, and elemental analysis. In the trimer, the three linear copper ions are bridged by two NTA carboxylate groups in a syn–anti conformation and connected by 4,4′-bpt to produce a 1-D array. Temperature-dependent magnetic susceptibilities reveal the presence of weak antiferromagnetic exchange between metal centers.     

Kinetics of 1-hexene dimerization catalyzed by a liquid-phase nickel complex

Reaction rates and activation energies for the oligomerization of 1-hexene catalyzed by a nickel complex of the formula Ni(F₃COO)(C₇H₁₅COO) have been measured at temperatures varying between 0 and 20°C. Diethyl aluminium chloride was used as cocatalyst.     

Configurational stabilization of mixed-valence states in the star-burst tetranuclear ruthenium complex bridged with acetylene links

A new tetranuclear ruthenium complex in which a metal was bridged radially to three identical metals with acetylene links showed a mixed-valence state in cyclic voltammograms. The peak potential difference for the mixed-valence state was twice the potential difference for a mixed-valence state of the corresponding binuclear complex. This fact suggests stabilization of the mixed-valence state twice by configurational modification of redox centers. However, this is inconsistent with the prediction from the additive pair model of the redox interaction. A quantum chemical model of the redox interaction was presented, in which the potential difference was expressed by the overlap integral S and the nearest neighbor interaction energy between the reduced center and the oxidized one. Application of the theory gave a negative value of S, which demonstrated reasonably the stabilization of the mixed-valence state from a quantum chemical viewpoint.     

Metallomacrocycle (MacM) complex with cyanide as bridged ligand: Electronic structures of [MacMCN]n

The electronic structures of complexes and one‐dimensional metallomacrocycles with cyanide as bridged ligand, such as [MacM(CN)₂]^? and [MacM(CN)]_n [Mac=phthalocyanine, tetrabenzoporphyrine; M=Co(III), Rh(III)] have been investigated using density functional theory. The results of this study show that the intrinsic semiconductivity properties depend on the frontier bands. The valence band is composed by the π‐macrocycle orbital. The conduction band for the cobalt polymers is a mixture of orbitals between this metal and the cyanide ligand along of the stacking direction. However, in the rhodium polymers such a band is exclusively composed of the π* system of the macrocycles. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002     

Syntheses,crystal structures,and magnetic properties of a series of Fe2Ln complexes

A family of phenoxo-bridged heterometallic Schiff base trinuclear complexes, [Fe₂LnL₂(C₃H₇COO)(H₂O)]·CH₃OH·CH₃CN·H₂O (Ln = Sm, 1; Gd, 2; Tb, 3; Dy, 4) is reported. Those complexes were afforded by “one-pot” reaction of a polydentate Schiff base ligand 2-hydroxy-3-methoxy-phenylsalicylaldimine (H₂L) with Fe(NO₃)₃·9H₂O, Ln(NO₃)₃·6H₂O and sodium butyrate (C₃H₇COONa) in a mixture of methanol and acetonitrile in the presence of triethylamine as a base. Single-crystal X-ray diffraction analysis reveals that the structures of the four complexes are isomorphic. In each complex, two anionic [FeL₂]^? units coordinate to the central lanthanide ion as a tetradentate ligand using its four phenoxo oxygens, forming a two-blade propeller-like molecular shape. Magnetic properties of 1–4 were investigated using variable temperature magnetic susceptibility, and weak ferromagnetic exchange between the Fe^III and Ln^III ions has been established for the Gd derivative. The Tb and Dy complexes show no evidence of slow relaxation behavior above 2.0 K.