Susumu Kitagawa

Synthesis, properties and crystal structures of dicopper(I) and disilver(I) complexes with 1,8-naphthyridine (napy): [Cu2(napy)2](ClO4)2 and [Ag2(napy)2](ClO4)2

Abstract Binuclear copper(I) and binuclear silver(I) complexes with 1,8-naphthyridine (napy) have been prepared. The crystal structures of [Cu 2 (napy) 2 ](ClO 4 ) 2 ( 1 ) and [Ag 2 (napy) 2 ](ClO 4 ) 2 ( 2 ) have been determined by using single crystal X-ray diffraction methods. Compound 1 crystallizes in space group P 1 , with a = 8.245(2), b = 10.376(2), c = 5.886(1) A, α = 84.06(2), β = 98.73(2), γ = 108.53(2) o and Z = 1; R = 0.047 for 1247 reflections. The cation of 1 , [Cu 2 (napy) 2 ] 2+ , is binuclear with two napy ligands bridging the two metals. The geometry of each Cu atom is nearly linear. Compound 1 , having a short Cu···Cu distance of 2.506(2) A, reversibly reacts with CO, acetylene and ethylene. Crystals of 2 are monoclinic space group P 2 1 / n with a = 16.017(7), b = 10.427(4), c = 5.752(2) A, β = 99.90(3) o and Z = 2; R = 0.088 for 1321 reflections. The structure of 2 is essentially the same as that of 1 . The Ag···Ag distance of 2.748(2) A is short compared with the corresponding distance in metallic silver 2.88 A.

Structural studies of copper(I) complexes with ethylene. Crystal structures of [Cu(2,2′-bipyridine)(ethylene)]ClO4 and [Cu(1,10-phenanthroline)(ethylene)]ClO4

Abstract The crystal structures of the complexes [Cu(2,2′-bipyridine)(ethylene)]ClO4 (I) and [Cu(1,10-phenanthroline)(ethylene)]ClO4 (II) have been determined from X-ray diffraction studies. Complex I crystallizes in the triclinic space group, P 1 , with four molecules in a unit cell of dimensions a 10.657(1), b 6.998(1), c 18.251(2) A, α 91.05(1), β 93.35(1), and γ 84.97(1)°. Complex II crystallizes in the monoclinic space group, P21/a, with four molecules in a unit cell of dimensions a 19.981(5), b 10.904(2), c 6.955(1) A, and β 103.90(2)°. Both structures were solved by heavy-atom methods, and refined by block-diagonal least-squares methods. The final R-values for I and II were 0.044 for 2225 observed reflections for I and 0.066 for 2005 observed reflections for II. In both crystals, the CuI ion is coordinated to two nitrogen atoms of 2,2′-bipyridine or 1,10-phenanthroline, and two carbon atoms of ethylene in an approximately planar form. The Cue5f8C bond distances of the coordinated ethylene molecules, 1.360(13) and 1.346(18) A for I and 1.361(22) A for II, do not show marked lengthening compared with that for free ethylene, and may be explained by dπ(Cu) → dπ (ethylene) back-bonding between the Cu 3dπ orbital and the Rydberg 3dπ orbital of the ethylene molecule.

Autoreduction of copper(II) complexes of 6,6'-dialkyl-2,2'-bipyridine and characterization of their copper(I) complexes

Abstract Copper(I) complexes of 6,6′-diakyl-2,2′-bipyridine (biL: alkyl = methyl, ethyl, and i-propyl) have been synthesized in acetone and ethanol. The resultant complexes are four-coordinate Cu(biL) 2 + , having pseudo-tetrahedral geometry. These give an intense metal-to-ligand charge transfer (MLCT) band at the visible region. The wavelength of the MLCT band decreases with the increase in bulkiness of an alkyl group. This is accounted for by the repulsive interaction between the copper atom and an alkyl group. The autoreduction of Cu(II)-6,6′-dialkyl-2,2′-bipyridine complexes in acetone and ethanol has been found. This is proved to be a thermal reaction due to its temperature-dependence. The reaction rate is strongly dependent on the alkyl substituents, a counter anion, and solvent. This reaction prefers ClO 4 − to Cl − as a counter ion of copper(II): moderately strong Cuue5f8Cl bond inhibits the formation of Cu(biL) 2 + . The substituents influence remarkably on the rate, which increases in the following order, methyl ⩾ ethyl > i-propyl. This is significantly associated with the precursor copper(II) complex.

Synthesis and crystal structures of tetra- and hexanuclear copper(I) complexes of pyrimidine derivatives, [Cu4(C4H8N2S)4](ClO4)4 and [Cu6(C5H5N2S)6]

Abstract 4-Hydroxy-6-methylpyrimidine-2-thione (Me(OH)pymtH) and 3,4,5,6-tetrahydropyrimidine-2-thione (H4pymtH) give hexanuclear and tetranuclear copper(I) complexes, [Cu6(C5H5N2S)6] (1) and [Cu4(C4H8N2S)4](ClO4)4 (2), respectively. Complex 1 crystallizes in the monoclinic space group C2/c, a=23.103(6), b=12.053(8), c=24.018(3) A, β=113.56(1)° and Z=4. Complex 2 crystallizes in the triclinic space group P 1 , a=12.005(2), b=19.597(3), c=11.609(2) A, α=105.61(1), β=101.23(1), γ=100.82(1)° and Z=2. The single-crystal X-ray structure of complex 1 reveals an anti-prismatic copper core of six copper atoms, each copper having a trigonal geometry with two thiolate sulfur donors and a nitrogen donor of a μ3-type Me(OH)pymt− ligand, while 2 affords a distorted tetrahedral core of four copper atoms containing only thione sulfur donors of an H4hpymtH ligand. 1H NMR spectra of the reaction solution demonstrate that 1 is the final product through the low-molecular weight polynuclear copper species of Me(OH)pymtH or its anionic form whereas 2 is the principal species of H4hpymtH even in solution.

Effect of substituents on the charge transfer band of copper(I) complexes with 4-monosubstituted pyridines

Abstract Copper(I) complexes with 4-substituted pyridine (L) (L = 4-CH3-py, 4-Cl-py, 4-CH3CO-py, 4-CN-py, and py) have been prepared and their electronic absorption spectra have been measured in the region of 20–30 kK. All the complexes give the broad metal-to-ligand charge transfer (MLCT) band assigned to Cu dπ-Ligand π*. The position of the MILCT band is mainly governed by the electron-withdrawing effect of the substituents, which is significantly associated with the stabilization of the pyridine ring π* orbitals. With the aid of the MLCT band, it is demonstrated that the monomer [CuL4] ClO4 is obtained from [Cu(CH3CN)4] ClO4 and the binuclear [CuClL2]2 forms from CuCl. The latter complex can reversibly react with carbon monoxide (CO) to give a carbonyl adduct (vco = 2060–2070 cm−1), while the former does not react with CO.

Structure of bis(2,6-dimethylpyridine)copper(I) perchlorate. The relationship between the Cu-N(pyridine) distance and Cu···CH3(methyl group) contacts

Abstract One of the conformational polymorphs of bis(2,6- dimethylpyridine)copper(I) perchlorate has been synthesized and its structure determined by single- crystal X-ray diffraction techniques. The crystals are monoclinic, space group Ia, with a = 14.858(3), b = 8.236(1), c = 16.308(2) A, β = 124.78(1)°, Z = 4; R was 0.070 for No= 1160 independent observed reflections. The coordination geometry around the Cu(I) atom is nearly linear with different Cuue5f8N distances, Cuue5f8N(1)=1.899(16) and Cuue5f8N(2)= 1.953(22) A. The dihedral angle between the pyridine planes is 56.2. The relationship between the Cuue5f8N- (pyridine) distance and Cu···CH3(methyl group) contacts has been discussed.

UV photoelectron spectra of some transition metal(II) acetylacetonates

The He(I) photoelectron spectra of acetylacetone (HAA) and its metallo complexes, M(II)(AA)2 (M(II) = Mn, Co, Ni, Cu and Zn), have been measured. These spectra show characteristic metal-dependence, from which the assignment is made. The order of the orbital energy level, d > π3 > n− > n+, holds for all the complexes reported here. The splitting of these orbitals is found to depend on the central metal ion specifically.

Preconcentration of some phosphorus-containing anions by adsorption on hydrated iron(III) oxide

Abstract The adsorption behaviour of orthophosphate, triphosphate, pyrophosphate, monomethylphosphate, phosphite, α- and β-glycerophosphates, dimethylphosphate, and hypophosphite on hydrated iron(III) oxide precipitate is studied as a function of pH. Orthophosphate is adsorbed quantitatively at pH 4.0–8.0, triphosphate and pyrophosphate at pH 4–9.3 and the next three compounds at pH 4–6.8. The last two ions were only slightly adsorbed at any pH examined.

Coordination power series of solvents : 2. The solvent effects on complex formations, half-wave potentials, 113Cd NMR resonances and Gibbs free energy changes of transfer

Abstract Coordination power ( CP ), a measure of a solvents donor ability, which is related to the Gibbs free energy change on the solvation of nickel(II) ion, was determined for some solvents. The solvent dependency of complex formations, polarographic half-wave potentials, Gibbs free energy changes of transfer, 113 Cd NMR chemical shifts and transfer activity coefficients were investigated for Cu 2+ , Cd 2+ , Ag + , Tl + and Li + on the basis of the concept of CP , indicating that the metal-solvent interaction depends on the hardness-softness of both the metal ion and the solvent. The CP series can be satisfactorily used for the metal ions such as Cu 2+ and Cd 2+ which resemble Ni 2+ ion in hardness- softness, and also roughly hold for the soft metal ions such as Ag + ion with the exception of soft nitrile and for hard metal ions such as Li + and Mg 2+ ions only in the solvents having the same donor atom. These results are supported by the facts that the stability sequence for nickel(II) complexes is the same as those for copper(II) and cadmium(II) complexes. The CP scale was compared with the α, σ, ϒ and donor number scales.

Copper-63 nuclear magnetic resonance studies of tris(triethyl phosphite)copper(I) chloride in nonaqueous solution

Abstract 63Cu and 31P NMR spectra of [CuL3Cl] (L=triethylphosphite (1)in various nonaqueous solvents have been measured. It has been demonstrated that ligand-dissociation of 1 occurs to give [CuL4]Cl (2) and low coordination copper(I) species. It has also been found that the formation of copper(I) species greatly depends on the solvent used. 1 and 2 give 63Cu NMR signals while 63Cu signals of other species are hardly observed due to significant line- broadening. By use of a dual NMR tube, 1 and 2 were determined quantitatively. It was found in a series of alcohols that 2 is preferred increasing solvent polarity. This is significantly associated with the cleavage of the Cuue5f8Cl bond.