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We investigated anodization of gold in aquaous solutions of carboxylic acids as a continuation of anodization of gold in oxalic acid. In contrast to the anodization in aquaous oxalic acid, in which...

Three new complexes with FeIII2(μ-O)(μ-OH) core surrounded with one, two, and three amino groups, that is, (6-amino-2-pyridylmethyl)bis(pyridylmethyl)amine (MAPA), bis(6-amino-2-pyridylmethyl)(pyri...

Ruthenium(II) complexes, [Ru(babp)(dmso)L], consisting of tetradentate square-planar ligand (babp = 6,6′-bis(benzoylamino)-2,2′-bipyridinato) and two monodentate axial ones, DMSO and L (L = dmso or...

In order to understand the effect of an oxygen-containing ligand on the physico-chemical properties and reactivities of hydrogenperoxocopper complexes, new copper(II) complexes with the N3O-type tr...

The bis-N,N-carboxymethy-(S)-phenylalaninato carbonato cobalt(III) complex, [Co(bcmpa)(CO3)]2−, has been prepared as a simple model that enables the recognition of an amino acid (Haa) whose coordination behaviours in solution have been characterized by electronic absorption (AB), circular dichroism (CD) and 1H NMR spectroscopies. The reaction of the K2[Co(bcmpa)(CO3)] complex with amino acids (Haa) has predominantly afforded the [Co(bcmpa)(aa)] complex in the trans(N)-configuration mode, rather than in the cis(N)-form. By using amino acid derivatives with bulky substituents at their amino or carboxylate sites under a neutral condition, the reactions have been demonstrated to be initiated by coordination of the amino nitrogen site. Interestingly, the cis(N)-complex, which is isolated as a minor product, isomerizes to the trans(N)-form in the presence of active charcoal under pH 7 in an aqueous solution. The site-selective coordination of Haa to the [Co(bcmpa)(CO3)]2− complex and the stereoselective isomeri...

The existence of a CH-π interaction has clearly been demonstrated by use of the ternary metal (Cu(II), Pd(II)) complexes involving o-/m-/p-methyl substituted L-phenylalanine (L-o-mPhe, L-m-mPhe, L-p-mPhe) and 1,10-phenanthroline (phen) on the basis of 1H NMR, electronic absorption, and CD spectroscopies, and X-ray diffraction method. The crystal structure of [{Cu(p-mPhe)(phen)}2{Cu(phen)2}(μ3-CO3)](ClO4)2 has revealed a marked structural feature suggesting CH-π and/or π–π interactions, although [Cu(L-o-mPhe)(phen)(H2O)]ClO4 does not show any interaction. CD spectra in the d–d region for [Cu(L-o-mPhe)(phen)]ClO4, [Cu(L-m-mPhe)(phen)]ClO4, and [Cu(L-p-mPhe)(phen)]ClO4 in aqueous solution have exhibited an obvious negative Cotton effect, and the magnitudes have significantly been reduced in dioxane/water in the order: [Cu(L-p-mPhe)(phen)]ClO4 ≤ [Cu(L-m-mPhe)(phen)]ClO4 < [Cu(L-o-mPhe)(phen)]ClO4. 1H NMR spectra of [Pd(L-o-mPhe)(phen)]ClO4, [Pd(L-m-mPhe)(phen)]ClO4, and [Pd(L-p-mPhe)(phen)]ClO4 have exhibited...

Redox reactions between horse heart cytochrome c and optically active Ru complexes were kinetically studied. The kinetic parameters for the oxidation of ferrocytochrome c with Ru III complexes indicated an apparent enantioselectivity, which clearly shows that exact molecular recognition is achieved through non-polar interactions rather than electrostatic ones.

Mononuclear copper complexes with a tripodal tetradentate ligand, tris(6-pivaloylamino-2-pyridylmethyl)amine (Htppa), and several anions have been prepared as a model metal centre of copper enzymes, whose structures have been examined by electronic absorption, ESR and NMR spectral, cyclic voltammetry, and X-ray diffraction methods. Those with an anion such as OH−, Cl−, Br−, and I− were shown to form a trigonal-bipyramidal geometry. The X-ray structures of [Cu(Htppa)](ClO4)2·2H2O·CH3OH, [CuCl(Htppa)]ClO4, [Cu(OH)(Htppa)]ClO4, [Cu(OH)(tppa)], and [Cu(tppa)](BPh4), obtained as a single crystal, revealed all trigonal-bipyramidal geometry with four nitrogen atoms of Htppa in trigonal plane and axial position and with the anion in another apical position. The reaction with NaN3 gave [Cu(N3)2(Htppa)], whose crystal structure was a square-pyramid with three nitrogen atoms of Htppa and N3− in square-planar positions and with another N3− in apical position. The redox potentials of [CuCl(Htppa)]ClO4 in MeCN or CH2Cl...

Cytochrome c553 and cytochrome b were isolated from soluble and membrane fractions of Alcaligenes xylosoxidans GIFU 1051, respectively, and their spectroscopic characterizations have been performed. Cytochrome c553 has been shown to be in the low spin state both in the oxidized and reduced forms at room temperature by the absorption and magnetic circular dichroism (MCD) spectra, while the high spin heme has been also observed in the cryogenic electron paramagnetic resonance (EPR) spectra. Exogenous small ligands such as NO and CO bind to cytochrome c553 by expelling the axial His ligand. The membrane-bound cytochrome b has two heme b centers in a protein molecule which are the active centers of NO reductase, the cytochrome bc complex, although the enzyme activity was rather low. The absorption, MCD, and EPR spectra of the membrane-bound cytochrome b showed that two heme b centers are in the different electronic states, the high and low spin states. Cytochrome c553 is the natural electron donor to the memb...

The crystal structures of trans-[Co(acac)2(PMePh2)2]PF6 (acac = 2,4-pentanedionate ion) (1), trans-[Co(acac)2(H2O)(PMePh2)]ClO4 (2), and trans(P,P)-[Co(acac)(CN)2(PMePh2)2] (3) were determined by the X-ray diffraction method. Complex 1 crystallizes in the monoclinic, space group P2/n, with two molecules in a unit cell of dimensions a = 17.151(2), b = 10.347(2), c = 10.996(2) A, β = 107.84(1)°, V = 1857.6(6) A3. Complex 2 crystallizes in the monoclinic, space group P21/c, with four molecules in a unit cell of dimensions a = 10.161(3), b = 17.291(5), c = 14.938(3) A, β = 91.76(2)°, V = 2623(1) A3. Complex 3 crystallizes in the monoclinic, space group C2/c, with four molecules in a unit cell of dimensions a = 21.628(1), b = 8.974(1), c = 16.203(1) A, β = 106.396(2)°, V = 3012.9(1) A3. The Co–P bond length for complex 1, 2.329(1) A, is significantly longer than those for complexes 2 (2.213(1) A) and 3 (2.2698(4) A). These lengths are discussed with the hydrolytic properties.

The single crystal of cis-β-Λ-S,S-[Co(CO3)(trien)](ClO4)·H2O (trien = triethylenetetramine) has spontaneously resolved from the aqueous solution of cis-α-[CoCl(NH3)(trien)](ClO4)2 containing hydrogencarbonate anion, whose crystal structure has been determined by X-ray diffraction method. The complex crystallizes in the monoclinic space group P21 with a = 7.410(1), b = 12.354(3), c = 8.676(1) A, β = 108.88(1)°, and Z = 2. The final R and Rw values for the 3056 observed reflections with Io > 3σ(Io) are 0.045 and 0.055, respectively. The tetradentate ligand, trien, is linked to the cobalt atom in cis-β-configuration, and the carbonato anion is coordinated to the metal atom as a didentate ligand. The Co–N bond lengths are 1.904(6), 1.928(4), 1.941(4), and 1.955(5) A, and the two Co–O bond lengths are both 1.909(4). The absolute configuration of the complex cation can be designated as Λ(λλδ) and those about two secondary nitrogen atoms are both S.

Structural and spectroscopic studies have been performed on the ternary Cu(II) complexes containing 4-halophenylalanines (XPhe) (X = I or Br) and 2,2′-bipyridine (bpy). The absorption spectra of the 1 : 1 : 1 Cu(bpy)(XPhe) systems exhibited a single d–d peak at 605—608 nm (pH 6—7), and the band centered at ca. 320 nm due to the charge transfer interaction between the substituted phenyl ring and bpy was observed in the difference spectra in the near ultraviolet region. Three complexes with XPhe, [Cu(bpy)(DL-IPhe)(NO3)] (1), [Cu(bpy)(DL-BrPhe)(NO3)] (2), and [Cu(bpy)(L-IPhe)]ClO4 (3) were isolated as crystals, and the structures were determined by the X-ray diffraction method. Complex 1 crystallizes in the monoclinic space group, P21/n, with four molecules in a unit cell of dimensions a = 5.292(1), b = 27.315(8), c = 13.848(2) A, β = 90.05(2)°. Complex 2 also crystallizes in the monoclinic space group, P21/n, with four molecules in a unit cell of dimensions a = 5.293(5), b = 27.18(1), c = 13.540(6) A, β = 9...

Full geometry optimizations have been carried out for the complex formations of Cu+ and Cu(2,2′-bipyridine)+ with CO2 by using the density functional methods. The calculation demonstrated that the end-on coordination mode was mainly favored for all cases, while the binding of 2,2′-bipyridine (bpy) to Cu(CO2)+ largely labilized the end-on coordination mode and stabilized the in-plane side-on coordination mode. The detailed examination of the population analysis indicate that the coordination of bpy to Cu+ weakens the electron donating character of CO2 to Cu+ and promotes the important participation of π-back-donative interaction from the metal ion to CO2.

The structures and the formation energies of [MCl4]2− (M = Cr, Mn, Fe, Co, Ni, Zn) have been examined by the density functional method. The optimized structures of [MnCl4]2−, [CoCl4]2− and [ZnCl4]2− are a regular tetrahedron with the M–Cl distances of 236, 227, and 231 pm, respectively. The structures of [CrCl4]2− and [FeCl4]2− are a flattened tetrahedron with the M–Cl distances of 236 and 231 pm, respectively, and with the flattening angles of 156 and 112°, respectively, while that of [NiCl4]2− is a tetrahedron elongated along an S4 axis with the Ni–Cl distance of 226 pm and the corresponding angle of 97°. The formation energies of [MCl4]2− have been compared with their experimental data, and the relative energies of the transformation from [M(H2O)6]2+ to [MCl4]2− are also evaluated in connection with the stability of the anions in aqueous solutions.

With a view to understanding the factors affecting the chemical properties of the copper sites in proteins, model copper(II) complexes of two multidentate ligands with nitrogen and sulfur atoms, 1,5-bis(2-pyridylmethylamino)-3-thiapentane (pmtp) and 2,6-bis(2,6-dithiaheptyl)pyridine (dthp), have been isolated as [Cu(pmtp)][Cu(pmtp)ClO4](ClO4)3 (1) and [Cu(dthp)(NO3)2] (2), respectively, and studied by X-ray diffraction, spectroscopic, and electrochemical methods. Complex 1 crystallizes in space group P21/a of the monoclinic system with four [Cu(pmtp)]2+ ions and four [Cu(pmtp)(ClO4)]+ ions in a cell of dimensions a = 24.180(7), b = 31.855(7), c = 9.760(3) A, and β = 143.84(1)°. The coordinations around the coppers in the two independent complexes are square-pyramidal and octahedral, respectively, with an amine nitrogen, two pyridine nitrogens, and a thioether sulfur at the equatorial positions (eq) and an amine nitrogen (and a perchlorate oxygen in addition in the octahedral complex) at the axial position...

The bis(diphenylphosphino)methane(dppm) compounds of copper(I), [Cu2(μ-dppm)2(biL)2](PF6)2 (biL=1,10-phenanthroline and its derivatives), have been synthesized and characterized by 1H and 31P NMR spectroscopy and X-ray crystallography. The molecules are found to contain a [Cu2(dppm)2]2+ framework with the two copper atoms bridged by two dppm ligands to give eight-membered C2P4C2 rings. This framework shows a staggered conformation subject to the coordination of additional ligands, biL. The coordination 1H and 31P shifts of the dppm are well-correlated with the basicity of the nitrogen donor atom of biL, sensitive to variations in the copper-ligand binding as well as their metal-to-ligand charge-transfer band. Crystallographic data of [Cu2(dppm)2(phen)2] are as follows, monoclinic space group P21⁄c, a=11.515(2) A, b=27.922(4) A, c=12.493(2) A, β=107.68(1)°, U=3827(1) A3, and Z=2.

Transformation among cobalt(II) dichloride hydrates in aqueous solutions was studied by the optical microscopic method. Although there are three hydrates (CoCl2·6H2O, CoCl2·4H2O, and CoCl2·2H2O) in the phase equilibrium diagram, the only solution mediated transformation between CoCl2·6H2O and CoCl2·2H2O could be observed under the present experimental conditions and it was confirmed that CoCl2·4H2O hardly formed compared with the other two hydrates. In order to investigate the reason why CoCl2·4H2O was hardly crystallized at the transformation from CoCl2·6H2O through CoCl2·2H2O and vice versa, the crystal structure of CoCl2·4H2O was investigated by the X-ray diffraction method. The structure of CoCl2·6H2O was reexamined because previously reported results had a relatively large R-factor. The crystal of CoCl2·4H2O is monoclinic, space group P21/a with a=11.548(1) A, b=9.342(1) A, c=6.056(1) A, β=110.79(1)°, and Z=4. The complex has a slightly distorted octahedral geometry about Co2+ ion and two Cl− ions ar...

The crystal structure of μ-oxo-bis[(octaethylporphinato)ruthenium(IV) chloride] benzene solvate, [Ru(IV)(oep)Cl]2O–C6H6, was determined by the X-ray method. The complex crystallizes in the tetragonal space group P4/nnc, a=13.912(2) A, c=17.821(4) A, and Z=2. The structure was solved by the heavy-atom method and refined to R=0.084 for 958 reflections. The [Ru(IV) (oep)Cl]2O complex has the crystallographic D4-422 symmetry and contains the binuclear (Cl)N4Ru–O–RuN4(Cl) coordination group with the Ru–O(μ) distance of 1.793(2) A, the Ru–Cl distance of 2.320(6) A, and the Ru–N distance of 2.038(9) A. The Ru–O–Ru bond is explicitly linear, and the two porphinato cores rotate around the Ru–O–Ru bond by 21.0° from the eclipsed form. The porphinato core is planar within 0.04 A, and the Ru atom is displaced only by 0.07 A out of the plane defined by the four porphinato nitrogen atoms toward the bridging O atom. These results are compared with those of the previously reported [Ru(IV)(oep)(OH)2]O–CH3OH crystal.

The photoacoustic spectroscopic technique was used to study in situ cathodic decomposition of CdS and ZnO semiconductor electrodes and electrochemical deposition of metal ions (Cd2+ and Zn2+) on the semiconductor electrodes.

The crystal structure of the title complex has been determined by the X-ray method. The complex crystallizes in the monoclinic space group P2/c with a=24.171(9), b=14.037(3), c=24.401(9) A, β=119.68(9)°, and Z=4. The structure was solved by the heavy-atom method and refined to R=0.094 for 3838 reflections. Two independent dimers exist with a crystallographically imposed two-fold axis in the unit cell. The two dimers are in an approximately orthogonal arrangement, and they take very similar conformations. The noticeable structural parameters are the average distances of 2.033(28) A for OsIV–N, 1.808(3) A for OsIV–O2−, and 1.997(29) A for OsIV–OCH3. The two porphinato cores bridged by a μ-oxo oxygen atom rotate around the approximately linear Os–O–Os bond (the average valence angle=178°) by 23(1)° from the eclipsed form. The porphine ring is planar within 0.10 A, and deviation of the Os atom from the porphinato plane of the four nitrogen atoms is 0.06 A. These results were compared, in the relation of the s...

The crystal structure of (octaethylporphinato)bis(tetrahydrofuran)iron(III) perchlorate was determined by the X-ray method. The complex crystallizes in the monoclinic space group C2/m, a=13.916(3) A, b=16.509(3) A, c=10.659(5) A, β=118.18(1)°, and Z=2. The structure was solved by the direct method and refined by the full-matrix least-squares method. The final R value was 0.079 for 597 reflections. The complex has a crystallo-graphically imposed twofold axis and a mirror of symmetry. The porphinato core is planar within 0.06 A. The iron(III) ion lies at the center of the octahedron formed by the four porphinato nitrogen atoms and the two tetrahydrofuran oxygen atoms. The axial Fe–O distance, 2.187(11) A, is considerably longer than the reported distances for high-spin porphinatoiron(III) complexes, while the equatorial Fe–N distance, 1.978(12) A, is comparable to those for low-spin and intermediate-spin porphinatoiron(III) complexes. The Fe–O and Fe–N bond distances are well explained in terms of an interm...

The crystal structure of diaqua(meso-tetraphenylporphinato)cobalt(III) perchlorate, [CoIII(tpp)(H2O)2]ClO4, has been determined by the X-ray method. The compound crystallizes in the monoclinic space group P21/c with four molecules in a unit cell of dimensions, a=13.93(4) A, b=23.46(2) A, c=17.35(6) A, and β=129.4(2)°. The Co(III) ion lies on the mean plane of the porphinato core, and is coordinated by the four porphinato nitrogen atoms and the two water oxygen atoms. The average Co–N distance is 1.964(4) A, and the average Co–O(water) distance is 1.936(5) A. The porphyrin plane is significantly ruffled and has an approximate S4-\bar4 symmetry. The perchlorate anion is not bound directly to the cobalt(III) ion, and links the two adjacent [CoIII(tpp)(H2O)2]+ cations by the hydrogen bonds with the aqua ligand oxygen atoms.

The crystal structure of the title complex was determined by X-ray diffraction: Orthorhombic, space group C2221, a=20.553(2) A, b=11.210(1) A, c=8.980(2) A, and Z=4. The structure was solved by the direct method and was refined anisotropically by the full-matrix least-squares method: R was 0.062 for 1206 observed reflections. The [Cu(bpy)2]+ cation has a pseudo-tetrahedral arrangemeni (average Cu–N=2.021 A). The interligand dihedral angle in [Cu(bpy)2]+, 75.2°, differs significantly from that previously reported [Cu(1,10-phenanthroline)2]ClO4 (49.9°).