Eiichi Miki

Vibrational spectroscopic study of light-induced metastable states of ethylenediaminenitrosylruthenium(II) complexes

Abstract Light-induced metastable states were found in trans - and cis -[RuCl(en) 2 NO]Cl 2 , trans - and cis -[RuBr(en) 2 NO]Br 2 , trans -[Ru(H 2 O)(en) 2 NO]Cl 3 , and a mixture of fac - and mer -[RuCl 3 (en)NO]. These states are formed when the polycrystalline samples are irradiated with blue or green laser lines from an Ar ion laser at 77 K. They decay upon irradiation with red light or a rise in temperature. The NO stretching frequency that is observed in the range from 1865 to 1904 cm −1 in the ground (normal) state of each compound shifts to the lower frequency side by approx. 100–140 cm −1 in the metastable states. These characteristics are similar to those of the metastable states of Na 2 [Fe(CN) 5 NO]·2H 2 O, K 2 [RuHCl 5 NO] and K 2 [Ru(NO 2 ) 4 (OH(NO)]. Decay temperatures of the ethylenediaminenitrosyl-ruthenium(II) complexes are notably higher (approx. 230–270 K) than those of the substances examined in earlier studies (approx. 180–190 K).

Electronic effects of the substituent group in 8-quinolinolato ligand on geometrical isomerism for nitrosylruthenium(II) complexes

Abstract The reaction of hydrous nitrosylruthenium trichloride with 2-chloro-8-quinolinol (H2cqn) or 2-methyl-8-quinolinol (H2mqn) in ethyl alcohol, 50 vol.% ethyl alcohol–water, water or acetic acid solution adjusted to pH 5.5 and the reaction of two kinds of geometrical isomers, cis -1 and cis -2[RuX(qn) 2 NO] (X=acetate or Cl; Hqn=H2cqn or H2mqn), with chloride or acetate ion in ethyl alcohol were examined in order to compare the effect of the chloro and methyl groups of the 2-position in 8-quinolinolato ligands on geometrical isomerism for nitrosylruthenium(II) complexes. The thermal and photoinduced reactions for the 2cqn complexes were also compared with those for the 2mqn complexes. The differences in the substituent in the 8-quinolinolato ligand and of the solvents used for the reactions were related to geometrical isomerism of the products. In general, the 2cqn complexes especially favor the cis -2 geometry, while the 2mqn complexes favor the cis -1 and trans geometries. The structures of cis -1[RuCl(2cqn) 2 NO], cis -2[RuCl(2cqn) 2 NO] and trans -[Ru(OEt)(2mqn) 2 NO] (OEt=ethanolate ion) were determined by X-ray diffraction.

Trans-influence of a coordinating nitrosyl group: preparation and structure of cis-trihalogeno(8-quinolinolato or its derivative)nitrosylruthenate(1−)

Abstract Hydrous nitrosylruthenium(III) halide reacts with 8-quinolinol or its derivative (2-methyl- or 5-chloro-8-quinolinol) in ethyl alcohol or acetonitrile to give [RuX3(N-O)(NO)]− [X = Cl or Br; H(N-O) = 8-quinolinol or its derivative]. All the halide ions are coordinated cis to the nitrosyl and the 8-quinolinolato oxygen trans to the nitrosyl, as found from an X-ray crystallographic study. The structure of the complex anion reflects a strong π-acceptor ability of the nitrosyl. The compounds obtained were also examined by 13C NMR and negative-SIMS (secondary-ion mass spectrometry).

Molecular vibrations and structure of the light-induced metastable state of [Fe(CN)5NO]2−

Abstract The molecular structure of the metastable state (MS1) of sodium nitroprusside was studied by polarized Raman spectroscopy and the normal coordinate analysis on 14 NO - and 15 NO -substituted crystals. The downshift of the bending mode of the Fe–(NO) bond upon 15 NO substitution is significantly smaller in MS1 than in the ground state. The normal coordinate analysis indicates that the effect of the N-atom mass on the mode is large in the Fe–N–O linkage but small in the Fe–O–N linkage. The small isotope shift observed in MS1 suggests the Fe–O–N linkage that was proposed in a recent X-ray diffraction study.

CRYSTAL STRUCTURES AND REVERSIBLE THERMAL ISOMERIZATION OF THREE GEOMETRICAL ISOMERS OF CHLOROBIS(2-ETHYL-8-QUINOLINOLATO) NITROSYLRUTHENIUM(II)

Abstract Crystal structures of the three geometrical isomers (1, 2 and 3) of [RuCl(2eqn)2NO] (H2eqn = 2-ethyl-8-quinolinol) have been determined by X-ray diffraction. The Cl atom is cis to the NO group in 1 and 2, and is trans to the NO group in 3. The N and O atoms of the two quinolinolato ligands for 1, 2 and 3 are in trans(N,N) and cis(O,O), in cis(N,N) and cis(O,O) and in trans(N,N) and trans(O,O) configurations, respectively. Crystallographic data for 1: triclinic, a = 10.140(4), b = 13.498(5), c = 7.902(3) A ; α = 94.08(3), β = 104.19(2), γ = 73.35(3)°, V = 1006.8(6) A 3 , Z = 2 , space group P 1 ; for 2; monoclinic, a = 14.730(2), b = 10.028(2), c = 13.761(4) A , β = 92.65(2)°, V = 2030.5(7) A 3 , Z = 4 , space group P21/a for 3: monoclinic, a = 14.830(4), b = 8.700(2), c = 16.711 (4) A , β = 110.40(3)°, V = 2021,0(9) A 3 , Z = 4 , space group Cc. The structures were solved by the heavy-atom method and were refined by fullmatrix (1 and 2) and block-diagonal (3) least-squares procedures to R = 0.0378 (1), 0.0320 (2) and 0.0397 (3) for 5207 (1), 4032 (2) and 1675 (3) reflections with I≥3 σ(I). The variable-temperature 1H NMR spectra in dimethyl sulfoxide-d6 revealed the steric hindrance due to the ethyl group of the quinolinolato ligands, reflecting the results of the crystal structure analysis. At high temperature (373–413 K), the reversible thermal isomerizaion reaction among the three isomers was observed un degassed dimethyl sulfoxide (DMSO). The mole ratio of 1, 2 and 3 was 19:4:1 at 413 K and did not depend on the starting species. Kinetic analysis revealed that the reaction was reversible between any two isomers and the isomerization between 1 and 3 proceeded by a mechanism distinct from the others.

Crystal structures of three geometrical isomers of [Ru(OAc)(2mqn)2NO] (OAc = acetate, H2mqn = 2-methyl-8-quinolinol) and their thermal isomerization reactions

Abstract The structures of three geometrical isomers of [Ru(OAc)(2mqn) 2 NO], one trans isomer and two cis isomers ( cis -1 and cis -2), were determined by X-ray diffraction. OAc in the cis - 1 ( 1 ) and cis -2 isomers ( 2 ) is cis to NO and the geometrics of the ligating N and O atoms in the two quinolinolato ligands are in cis (O,O) and trans (N,N) configurations for 1 and in cis (O,O) and cis (N,N) for 2 . In the trans isomer ( 3 ), OAc is trans to NO and the geometry is in trans (O,O) and trans (N,N) configurations. The RuO(OAc) bond for 3 was shorter than those for 1 and 2 , and the RuO(2mqn) bond trans to NO was also shorter than that cis to NO due to a trans -strengthening effect of NO. Reversible thermal isomerization between 1 and 2 , and the irreversible one from 3 to 1 and 2 were observed in deaerated N , N -dimethyl-formamide at higher than 353 K.

Preparation and characterization of cis- and trans-[Ru(OAc)(2mqn)2NO] (OAc=acetate, 2mqn=2-methyl-8-quinolinolate), and their mutual photoisomerization reactions

Abstract A mixture of hydrated nitrosylruthenium(III) chloride and 2-methyl-8-quinolinol (H2mqu) (1:4 molar ratio) in acetic acid aqueous solution adjusted to pH 5.5 and warmed at c. 70 °C for 2 h led to preparation of cis- [Ru(OAc)(2mqn)2NO] which has cis(0,0) and trans(N,N) configuration for the ligating atoms of the 2mqn ligands. The trans isomer was photochemically prepared from the cis isomer in CH2Cl2 using an Xe lamp as the light source. The photoisomerization in deaerated CH2Br2 was examined at −5 to 30 °C using a super high-pressure Hg lamp (436 mm). Quantum yields of the cis to trans and the trans to cis isomerizations were 1–2.5×10−3 and 8–11×10−3, respectively. Solvent effect studies by adding liquid paraffin to the CH2Br2 solution on the photoreaction and the NO scramble on the irradiation in the presence of 15NO gas showed that RuNO bond rupture takes part in the isomerization.

Relationship between pKa of 8-quinolinol derivatives and a π-donor ability of the 8-quinolinolato oxygen in linear nitrosylruthenium(II) complexes

Abstract The relationship between the pKa of 8-quinolinol derivatives {8-quinolinol (Hqn), 2-methyl- (H2-Meqn), 2,4-dimethyl- (H2,4-diMeqn), 5-chloro- (H5-Clqn) and 5,7-dichloro-8-quinolinols (H5,7-diClqn)} and a π-donor ability of the 8-quinolinolato oxygens has been investigated by the identification of the structures of the major products, [RuCl(QN)(QN′)NO] (HQN=8-quinolinol derivative; HQN′=different 8-quinolinol derivatives), obtained by the reaction of [RuCl3(QN or QN′)NO]− with HQN′ or HQN. The results obtained clearly showed that the oxygen of the 8-quinolinol derivative that has a higher pKa predominantly coordinates in the trans position to the NO ligand and is a better π-electron donor. The order of the π-electron donor ability for the oxygen of the 8-quinolinol derivatives is as follows: H2-Meqn≥H2,4-diMeqn>Hqn≥H5-Clqn>H5,7-diClqn, almost agreeing with the magnitude of the pKa values of the corresponding 8-quinolinols. The structures of cis-1 [RuCl(5,7-diClqn)2NO] and cis-1 [RuCl(5,7-diClqn)(2-Meqn)NO] were determined by X-ray diffraction.

Reaction of hydrous nitrosylruthenium trichloride with 2-pyridinemethanol

The reaction of hydrous nitrosylruthenium trichloride with an excess of 2-pyridinemethanol (H2pm) in boiling ethyl alcohol gave [H 2 2pm][RuCl 3 (2pm)NO] (H 2 2pm=the proton adduct of H2pm, 2pm=2-pyridinemethanolate ion) ( 1 ) and [RuCl 2 (2pm)(H2pm)NO] ( 2 ). [RuCl(2pm) 2 NO] ( 3 ) was isolated by heating complex 2 in boiling water. The reaction of hydrous nitrosylruthenium trichloride with an excess of H2pm in boiling water gave a slight amount of complex 4 , a geometrical isomer of 3 , together with 2 and 3 . Na[RuCl 3 (2pm)NO]·H 2 O ( 5 ) was prepared from 1 by an anion-exchange chromatography. The complexes obtained were {Ru(II)–NO + } type octahedral complexes. The structures of 1 , 2 and 4 were determined by X-ray crystal analysis. The alcoholato oxygen of 2pm in 1 , 2 or 4 coordinates trans to the NO. For [RuCl 3 (2pm)NO] − in 1 , the three Cl atoms are cis to the NO. For 2 , the ligating N atom of the H2pm is trans to the N atom of the 2pm. For 4 , the Cl atom is cis to the NO and the geometry of the ligating N and O atoms of the two 2pm is in cis ( N,N ) and cis ( O,O ) configuration. The proton NMR spectra showed that, for 3 , the Cl atom is cis to the NO and the geometry of the ligating N and O atoms of the two 2pm is in trans ( N,N ) and cis ( O,O ) configuration and the structure of the complex anion in 5 is the same as that in 1 . In 1 , a strong interaction between [H 2 2pm] + and [RuCl 3 (2pm)NO] − through the proton of [H 2 2pm] + was observed in the solid state and reflected on the electric conductivity in DMF. The protonations to 2 and 3 were observed in the aqueous solution. Changes of 2 to 3 at 373 K and of 3 to 2 in the presence of DCl at room temperature were observed in DMSO.

Molecular geometries, vibrational analysis, bonding and molecular orbitals of the three isomers of [RuCl(qn)2NO] (Hqn=2-methyl-8-quinolinol or 2-chloro-8-quinolinol): density functional theory studies

Abstract The geometries of the three isomers of [RuCl(qn) 2 NO] {Hqn=2-methyl-8-quinolinol (H2mqn) or 2-chloro-8-quinolinol (H2cqn)} were calculated with the restricted Hartree–Fock and different DFT methods. The B3PW91 method gave the best performance in the calculation for predicting the structure and vibrational spectrum of this series of complexes. The deviation between the calculated and the observed NO harmonic stretching frequencies was about 1% for these complexes. Furthermore, the IR bands containing the vibration of RuN, RuO and RuCl of the complexes were successfully assigned with the help of theoretical calculations. The electronic structures of the complexes were calculated at B3PW91/Lanl2dz level. The different bonding characteristic of the RuNO for the cis types of the 2cqn and 2mqn complexes was determined by the NBO population analysis. For both the 2mqn and 2cqn complexes, the HOMO is best described as a ligand based orbital which contains a small amount of Ru and NO character, while the LUMO is best represented by an antibonding overlap of the Ru(d) and π* NO(p) orbitals. There is a large degree of mixing between the NO and the metal d orbitals in the frontier orbitals, indicating that the peculiarity of the {Ru II NO + } group affects the synthesis, structure and reactivity of nitrosylruthenium(II) complexes containing 8-quinolinol and its derivatives. The DFT calculations suggest that the trans isomers are more difficult to prepare than the respective cis isomers, which explains the experimental observations.