Yasuo Nakao

Syntheses, crystal structures and autoreduction behavior of antiferromagnetically coupled dicopper(II) oximato complexes

Abstract Four dicopper(II) oximato complexes of 2-[2-(α-pyridyl)methyl]imino-3-butanone oxime (pmiboH) and 2-[2-(α-pyridyl)ethyl]imino-3-butanone oxime (peiboH), [Cu2(pmibo)2](ClO4)2 (1), [Cu2(pmibo)2](NO3)2·CH3OH (2), [Cu2(peibo)2](ClO4)2·CH3OH (3) and [Cu2(peibo)2(H2O)2](ClO4)2 (4), were prepared and characterized structurally and magnetically. All the dicopper(II) oximato complexes have a common cationic structure in which the two Cu atoms are bridged through two NO bridges of the oximato ligand to afford a dinuclear structure. The cation moieties of 1 and 2 consist of one six-membered Cu2N2O2 chelate ring and four five-membered (CuN2C2 and CuNC2N) chelate rings, providing a planar configuration. The cation moieties of 3 and 4 are also composed of three six-membered (Cu2N2O2 and CuNC3N) chelate rings and two five-membered CuN2C2 chelate rings, giving a twisted-boat configuration. The −2J values (H=−2JS1S2) are 835, 825, 550 and 510 cm−1 for 1, 2, 3 and 4, respectively, indicative of a strong antiferromagnetic interaction in the solid state. All the dicopper(II) oximato complexes show seven 1H NMR signals at 23°C in the range of −0.5 to 30 ppm with the linewidths at half-height, Δν1/2 of 60–1500 Hz, which is characteristic of antiferromagnetic species and indicates that the dinuclear structure is kept in solution. The −2J values reflect the degree of distortion from the planarity of the Cu2 framework. The −2J values roughly correlate with the 1H NMR parameters; the larger the −2J values, the smaller the chemical shifts and linewidths. Complexes 1 and 2 were found to undergo an autoreduction reaction in dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA), and their behaviors were first monitored by UV–Vis and 1H NMR methods.

Copper(II) complexes with tripodal imidazole-containing ligands. Structure-electrochemistry relationship

Mono- and dimeric copper(II) complexes of tris- (benzimidazol-2-ylmethyl)amine (L1) and of its derivatives with the imidazole NH protons substituted by a methyl (L2), ethyl (L3), benzyl (L4) or o-methylbenzyl (L5) group were prepared and characterized based on magnetic susceptibility, conductivity, cyclic voltammetric half-wave potential (E12), infrared, electronic and ESR spectra. The complexes containing H2O, NO3−, Cl−, Br−, N3−, and N-methylimidazole with L1–L5 were mononuclear copper(II) complexes, while the complexes with NCS− or NCO− and L1–L3 [except [Cu(L1)NCS](NO3)] were dinuclear ones, which dissociate to monomeric complexes in DMF solution. The E12 values of copper(II) in a series of complexes containing H2O or NO3− decrease in the order L5 > L1 > L2 > L3 > L4, whereas those in complexes with Br− and N-methylimidazole decrease in the orders L4 ≳ L5 > L1 > L2 > L3 and L5 > L1 > L4 ≳ L2 > L3, respectively. The relationship between the structure of the complexes and the E12 values are discussed in some detail.

Copper(III) and nickel(III) complexes of tripeptides, dipeptide schiff bases and related ligands

Abstract Trivalent copper and nickel complexes of tripeptides, dipeptide Schiff bases and related ligands were comparatively studied by cyclic voltammetry. Depending upon the nature of the coordinated groups and the structure of fused ring systems the electrode potentials of Cu(III)Cu(II) and Ni(III)Ni(II) couples vary in the range 0.7–1.4 V. The stronger donating groups such as amino and deprotonated amide nitrogens assist the stabilizing of metal ions in the higher oxidation state, although aromatic nitrogen and oxygen do not contribute effectively for this. The trivalent copper and nickel with smaller ionic radii are stabilized by the 5-5-5 but not by the 5-6-5 or 6-5-6 fused ring structure as in bivalent copper and nickel. These redox characters were related with ESR and the absorption spectral feature of parent and trivalent metal complexes.

X-Ray crystal structures and magnetic properties of azide-bridged binuclear copper(II) complexes containing the Schiff-base ligand derived from 2-pyridinecarbaldehyde and histamine. Structure–magnetism relationship

The structures of the complexes [Cu2(L1)2(N3)2][ClO4]2(1){ L1= 1-(imidazol-4-yl)-2-[(2-pyridylmethylene)amino]ethane} and [Cu2(L1)2(N3)3]Cl·2H2O (2) have been determined by X-ray methods. Complex (1) contains discrete [Cu2(L1)2(N3)2]2+ cations which are located at centres of inversion. The geometry around each copper(II) ion is square pyramidal. The two basal planes in the complex cation are parallel and separated by 2.64 A. The two azide ions which are parallel to each other bridge in an end-on fashion between a basal position of one square pyramid and an apical position of the other. Magnetic susceptibility data for (1) show a ferromagnetic interaction (Weiss constant θ=+23 K) above 200 K. On the other hand, below 200 K, it is considered that there is a weaker exchange interaction than that above 200 K. In differential scanning calorimetry curves for (1), small thermal anomalies have been observed over the temperature range 150–250 K. Complex (2) contains an azide-bridged, centrosymmetric copper(II) dimeric cation. The five-coordinate geometry around each copper(II) ion is square pyramidal. An azide ion bridges in an endto-end fashion between the two apical positions of two square pyramids. A very weak antiferromagnetic exchange interaction is found for (2)(0 J–0.5 cm–1, where J denotes the exchange integral defined by the Hamiltonian ℋ=–2JS1S2).

The monomeric and dimeric copper(II) complexes containing imidazole and dipeptides

Abstract The mixed ligand copper(II) complexes with imidazole and glycylglycine or glycyl-β-alanine were prepared in neutral and basic solutions. The copper(II) complexes obtained in neutral solutions were mononuclear complexes, while those in basic solutions were binuclear complexes bridged by imidazolate. In the cases of the binuclear complexes, it was found that the two copper(II) ions are antiferromagnetically coupled with -J values of 19–17 cm −1 . It has also been disclosed on the basis of visible and ESR spectral measurements that these dimeric structures are maintained in the concentration of 1.3 × 10 −2 to 1.2 × 10 −3 M /Cu.

Monomeric and dimeric copper(II) complexes composed of some terdentate schiff bases and oxalate, oxamate, azide, thiocyanate or cyanate ions

Abstract Monomeric and dimeric copper(II) complexes containing the Schiff bases derived from 2-pyridinecarbaldehyde and histamine (2-PcaHist), 2-(2-aminoethyl)pyridine (2-Pca2-Aep), or β-alanine (2-Pcaβ-Ala), and oxalate (ox), oxamate (om), azide, thiocyanate, or cyanate ions have been prepared and characterized based on their electronic, infrared and electron spin resonance spectra, and magnetic susceptibilities. The structure of the monomeric copper(II) complex, [Cu(2-PcaHist)(N3)2] has been determined by the X-ray diffraction method. The crystal of [Cu(2-PcaHist)(N3)2] is triclinic, with a = 10.262(8), b = 9.177(6), c = 7.688(5) A, α = 104.42(4), β = 94.09(4), γ = 92.64(4)°, Z = 2, and space group P 1 . The five-coordinate geometry around copper(II) ion is intermediate between trigonal-bipyramid and square-pyramid. The half-field absorption in the ΔMs = 2 region of powdered X-band ESR spectra was scarcely observed for [Cu(2-Pca2-Aep)(N3)2], [Cu(2-Pca2-Aep)(NCS)2], [Cu(2-Pca2-Aep)(NCO)2] and [Cu(2-PcaHist(N3)2]. The compounds [Cu2(2-PcaHist)2(N3)3]Cl·2H2O and [Cu2(2-PcaHist)2(N3)2](ClO4)2 which are considered to have a dimeric structure exhibited the half-field absorption in the same region. However, an exchange interaction was hardly observed down to 4.2 °K in the magnetic susceptibility measurement for [Cu2(2-PcaHist)2(N3)3](Cl·2H2O. The susceptibility of an oxalate-bridged copper(II) complex, [Cu2(2-PcaHist)2(ox)](ClO4)2, showed an antiferromagnetic interaction (J = −21.5 cm−1) and the X-band ESR spectrum for the powdered sample showed a very weak absorption for the triplet state of such a dimer in the ΔMs = 2 region.

Synthesis, structures and properties of the dinuclear copper(II) complexes triply bridged by two oximato and one pyrazolato or one phthalazine

Abstract The triply (two oximato and one pyrazolato or one phthalazine) bridged dinuclear copper(II) complexes [Cu2(L1)2(pz)]ClO4 (1) and [Cu2(L1)2(phta)](ClO4)2 (2) (HL1=2-[2-(α-pyridyl)ethyl]imino-3-butanone oxime, pz=pyrazolate anion, phta=phthalazine) were synthesized and characterized; the crystal structures of 1 and 2 were determined by X-ray crystallography. Magnetic susceptibility measurements from liquid helium temperature to room temperature showed a weak antiferromagnetic exchange coupling between two copper(II) ions (2J=−17 cm−1) for l, on the other hand, a very strong antiferromagnetic interaction for 2 was observed (2J=−760 cm−1).

Syntheses and X-ray crystal structures of tetranuclear [Ag4(μ3-S2O3)(μ-S2O3)(μ-dppm)4] {dppm=bis(diphenylphosphino)methane} and trinuclear [Ag3(μ3-Cl)(μ-S2O3)(μ-dppm)3] clusters

The reaction between AgClO 4 , dppm and Na 2 S 2 O 3 ·5H 2 O affords the tetranuclear [Ag 4 (μ 3 -S 2 O 3 )(μ-S 2 O 3 )(μ-dppm) 4 ] cluster, in which the four Ag atoms form a square bridged by four dppm ligands and the two thiosulfate ligands are bound on both sides of the Ag 4 plane. The S atom of one thiosulfate ion forms bonds with three Ag atoms, while the S atom of the other forms bonds with two Ag atoms. The trinuclear [Ag 3 (μ 3 -Cl)(μ-S 2 O 3 )(μ-dppm) 3 ] cluster is obtained by a reaction of AgCl with dppm and Na 2 S 2 O 3 ·5H 2 O. The structure of the cluster comprises an Ag 3 triangle bridged by three dppm ligands. The S atom of the thiosulfate ion forms a double bridge at the edge of the triangle from one side of the Ag 3 plane and the chloride ion forms a triple bridge from the other side of the Ag 3 plane.

Synthesis, structure and characterization of dinuclear nickel(II) complexes containing the derivatives of N,N,N′,N′-tetrakis- [(2-benzimidazolyl)methyl]-2-hydroxy-1,3-diaminopropane and an acetate or a propionate ion

The dinuclear nickel(II) complexes [Ni 2 (L 1 )(OAc)(H 2 O) 2 ](ClO 4 ) 2 ·3H 2 O ( 1 ), [Ni 2 (L 2 )(OAc)(H 2 O) 2 ](ClO 4 ) 2 ( 2 ) and [Ni 2 (L 2 )(OPr)(H 2 O) 2 ](ClO 4 ) 2 ·H 2 O ( 3 ) (HL 1 = N,N,N′,N′ -tetrakis[(1-methyl-2-benzimidazolyl)methyl]-2-hydroxy-1,3-diaminopropane, HL 2 = N,N,N′,N′ -tetrakis[(1-ethyl-2-benzimidazolyl)methyl]-2-hydroxy-1,3-diaminopropane, OPr = propionate anion) were synthesized and characterized. The crystal structures of [Ni 2 (L 2 )(OAc)(CH 3 OH) 2 ](ClO 4 ) 2 ·CH 3 OH·H 2 O ( 2 ′) and [Ni 2 (L 2 )(OPr)(CH 3 OH) 2 ](ClO 4 ) 2 ·CH 3 OH·2H 2 O ( 3 ′), which become 2 and 3 upon exposure of 2 ′ and 3 ′ to air, respectively, were determined by X-ray diffraction. 2 ′ and 3 ′ are isostructural. They consist of dinuclear cations and uncoordinated perchlorate ions. In the complex cations, the two nickel(II) centers are in a distorted octahedral coordination with an alkoxo and an acetato or a propionato bridge. The distances between the two nickel(II) ions are 3.521(2) and 3.507(2) A for 2 ′ and 3 ′, respectively. Variable temperature magnetic susceptibility measurements of 2 and 3 show an antiferromagnetic exchange coupling (2 J = −43.2 cm −1 for 2 , and 2 J = −34.4 cm −1 for 3 , H = −2 JS 1 · S 2 ) between two nickel(II) ions.

Crystal and molecular structure of sodium µ-(imidazol-1-yl-NN′)-bis-[(glycylglycinato-NN′O)cuprate(II)] hexahydrate: structure–magnetism relationship in imidazolate-bridged binuclear copper(II) complexes

The structure of the title complex, Na[Cu2(Gly-GlyO)2(im)]·6H2O [Gly-GlyO = glycylglycinate(2–), im = imidazolyl), has been determined from X-ray diffractometer data, to give final discrepancy indices of R= 0.0302, and R′= 0.0391. The complex crystallizes in the triclinic space group P with unit-cell dimensions a= 11.246(4), b= 10.464(3), c= 10.858(4)A, α= 109.99(3), β= 115.05(3), γ= 85.05(3)°, and Z= 2. Each copper(II) atom has square-planar co-ordination by amino-nitrogen, deprotonated amide nitrogen, carboxylate oxygen of the glycylglycinate ligand, and by nitrogen of bridging imidazolate, to form altogether a binuclear copper(II) complex. The complex is almost planar and has an approximate two-fold axis which is coincident with that of the imidazolate ring. Variable-temperature magnetic susceptibility data measured down to 4.2 K show an antiferromagnetic exchange interaction with a coupling constant J=–19 cm–1. The bridging imidazolate plane and copper(II) co-ordination planes make an angle of 5.8° for Cu(1) and 10.4° for Cu(2). The relative orientation of the bridging imidazolate and the copper(II) co-ordination planes does not seem to be responsible for the magnitude of the magnetic exchange coupling constant (J=–19 cm–1) in this case. It is concluded that a π-exchange mechanism is not important in the imidazolate-bridged binuclear copper(II) complexes.