Kiyoshi Tsuge

Reversible Mechanochromic Luminescence of [(C6F5Au)2(μ-1,4-Diisocyanobenzene)]

Reversible mechanochromic luminescence of [(C6F5Au)2(mu-1,4-diisocyanobenzene)] is reported. Grinding of the complex induced a photoluminescent color change, which was restored by exposure to a solvent. This cycle was repeated 20 times with no color degradation in the emissions. Their optical properties, X-ray crystallographic analysis, IR, and XRD measurements strongly suggested that the change in the molecular arrangement is responsible for this mechanochromic property. Intermolecular aurophilic bondings presumably play a key role in the altered emission.

Octa(μ3‐selenido)hexarhenium(III) Complexes Containing Axial Monodentate Diphosphine or Diphosphine–Monoxide Ligands

A series of the octahedral hexarhenium(III) complexes containing a variable number of diphosphine (diphos) or diphosphine-monoxide (diphosO) ligands have been prepared by the substitution of the diphosphine Ph2P(CH2)nPPh2 (n = 1 to 5) for the iodide ions in the parent octahedral hexarhenium cluster compound [Re6Se8I6]3-. The diphosphine Ph2P-(CH2)nPPh2 ligands adopt an eta1-bonding mode with the Re6(mu3-Se)8 core, and the P donor atom in the pendant arm is noncoordinated and oxygenated in most cases. The series of new hexarhenium(III) complexes have been well-defined by 1H, 13C, and 31P NMR spectroscopic and FAB-MS data. Four compounds among the series were characterized by X-ray structural determination. Geometrical isomers were identified by NMR spectroscopy as well as by the structural determinations. The apical ligand substitution induces significant change in the redox potentials and the photophysical properties of the Re6(mu3-Se), core. The E1/2 value of the reversible process ReIII6/ReIII5ReIV becomes more positive with the increasing number of the coordinated P donors. The phosphine-substituted hexarhenium(III) derivatives are highly luminescent, with microsecond scale emissive lifetime at ambient temperature, and the fully substituted derivatives with the formula [Re6Se8-(eta1-diphosO)6]2+ display the strongest luminescence with the longest emission lifetimes.

Photo- and Vapor-Controlled Luminescence of Rhombic Dicopper(I) Complexes Containing Dimethyl Sulfoxide

Halide-bridged rhombic dicopper(I) complexes, [Cu2(μ-X)2(DMSO)2(PPh3)2] (X = I(-), Br(-); DMSO = dimethyl sulfoxide; PPh3 = triphenylphosphine), were synthesized, the iodide complex of which exhibited interesting photochromic luminescence driven by photoirradiation and by exposure to DMSO vapor in the solid state. Single-crystal X-ray diffraction measurements revealed that the iodo and bromo complexes (abbreviated Cu2I2-[O,O] and Cu2Br2-[O,O]) were isomorphous, and that the two DMSO ligands were coordinated to the Cu(I) ion via the O atom in both complexes. Both complexes exhibited bright blue phosphorescence at room temperature (λ(em) = 435 nm, Φ(em) = 0.19 and 0.14 for Cu2I2-[O,O] and Cu2Br2-[O,O], respectively) with a relatively long emission lifetime (τ(em) ~ 200 μs at 77 K) derived from the mixed halide-to-ligand and metal-to-ligand charge transfer ((3)XLCT and (3)MLCT) excited state. Under UV irradiation, the blue phosphorescence of Cu2Br2-[O,O] disappeared uneventfully and no new emission band appeared, whereas the blue phosphorescence of Cu2I2-[O,O] rapidly disappeared with simultaneous appearance of a new green emission band (λ(em) = 500 nm). On further irradiation, the green emission of the iodide complex gradually changed to bright yellowish-green (λ(em) = 540 nm); however, this change could be completely suppressed by lowering the temperature to 263 K or in the presence of saturated DMSO vapor. The initial blue phosphorescence of Cu2I2-[O,O] was recovered by exposure to DMSO vapor at 90 °C for a few hours. IR spectroscopy and theoretical calculations suggest that the DMSO ligand underwent linkage isomerization from O-coordination to S-coordination, and both the occurrence of linkage isomerization and the removal of DMSO result in contraction of the rhombic Cu2(μ-I)2 core to make the Cu···Cu interaction more effective. In the contracted core, the triplet cluster-centered ((3)CC) emissive state is easily generated by thermal excitation of the (3)XLCT and (3)MLCT mixed transition state, resulting in the green to yellowish-green emission. In contrast, the Cu···Cu distance in Cu2Br2-[O,O] is considerably longer than that of Cu2I2-[O,O], which destabilizes the (3)CC emissive state, resulting in the nonemissive character.

Monodentate and bridging coordination of 2,5-dimercapto-1,3,4-thiadiazolate to a (2,2′:6′,2″-terpyridine)platinum(II) center

A series of mono- and di-nuclear platinum complexes, [Pt(trpy)(McMT)](PF6) (1), [Pt(trpy)(DMcTH)](PF6) (2) and [(Pt(trpy))2(DMcT)](PF6)2 (3) has been synthesized by the reaction of [Pt(trpy)(OH)](PF6) with mercapto- and dimercapto-thiadiazoles (trpy = 2,2′:6′,2″-terpyridine, McMTH = 2-mercapto-5-methyl-1,3,4-thiadiazole, DMcTH2 = 2,5-dimercapto-1,3,4-thiadiazole). The X-ray structure determinations revealed that the mercaptothiadiazoles coordinate to the platinum centers as κ1S-thiolate forms in all three complexes. Mononuclear DMcT–Pt complex 2 has a free thioamide group which is responsible for the formation of a hydrogen-bonded dimeric structure in the solid state. The complexes 1 and 2 show LLCT emissions in the solid state, whereas 3 is non-emissive. Cyclic voltammograms of the three complexes in DMF commonly show two reduction processes at ca. −0.7 V and −1.3 V based on the {Pt(trpy)}2+ units. Complex 2 further shows the oxidation of a free thioamide group at 0.32 V (vs. Ag/AgCl) on the addition of Et3N.

Directional Energy Transfer in Mixed-Metallic Copper(I)–Silver(I) Coordination Polymers with Strong Luminescence

Strongly luminescent mixed-metallic copper(I)-silver(I) coordination polymers with various Cu/Ag ratio were prepared by utilizing the isomorphous relationship of the luminescent parent homometallic coordination polymers (Φ(em) = 0.65 and 0.72 for the solid Cu and Ag polymers, respectively, at room temperature). The mixed-metallic polymer with the mole fraction of copper even as low as 0.005 exhibits a strong emission (Φ(em) = 0.75) from only the copper sites as the result of the efficient energy migration from the silver to the copper sites. The migration rates between the two sites were evaluated from the dependence of emission decays upon the mole fraction of copper.

Stabilization of [Ru(bpy)2(CO)(η1-CO2)] and unprecedented reversible oxide transfer reactions from CO32− to [Ru(bpy)2(CO)2]2+ and from [Ru(bpy)2(CO)(η1-CO2)] to CO2

Abstract Unusual thermal stability of [Ru(bpy)2(CO)(η1-CO2)] (1) as a metal–η1-CO2 complex was examined both in solid state and in solution. Compound 1 dissolves in CH3CN containing LiCF3SO3. Interaction between Li+ and the η1-CO2 group enhances an electron flow from Ru to the CO2 ligand and greatly contributes to the stabilization of the Ru–η1-CO2 bond. The reaction of [Ru(bpy)2(CO)2](PF6)2 with [Crown·K]2CO3 in dry CH3CN selectively produced 1 through the 1:1 adduct with the RuC(O)–OCO2 moiety. Stoichimetric formation of 1 from the 1:1 adduct is also assisted by [Crown·K]+ as a Lewis acid. Similarly, the reaction of [Ru(bpy)2(CO)2](PF6)2 with (Me4N)2CO3 in DMSO gave the 1:1 adduct in the initial stage, which gradually changed to a metalloanhydride complex, [Ru(bpy)2(CO)((CO)2O)] due to the absence of Lewis acids to stabilize 1, since an addition of LiCF3SO3 to the solution gave [Ru(bpy)2(CO)(η1-CO2)] quantitatively.

Mononuclear oxovanadium complexes of tris(2-pyridylmethyl)amine

Mononuclear oxovanadium(IV) and dioxovanadium(V) complexes of tris(2-pyridylmethyl)amine (tpa) have been prepared for the first time. Crystal structure determinations of three oxovanadium(IV) complexes, [VO(SO4)(tpa)], [VOCl(tpa)]PF6, or [VOBr(tpa)]PF6, and a dioxovanadium(v) complex [V(O)2(tpa)]PF6 disclosed that the tertiary nitrogen of the tpa ligand always occupies the trans-to-oxo site. The structures of an oxo-peroxo complex [VO(O2)(tpa)]Cl that was prepared previously and of a mu-oxo vanadium(III) complex [{VCl(tpa)}2(mu-O)](PF6)2 have also been determined. The tertiary nitrogen is located at a trans site to the peroxo and chloride ligands, respectively. The total sums of the four V-N bond lengths from the tpa ligand are remarkably similar among the six complexes, indicating that the vanadium oxidation states become less influential in tpa bonding due primarily to the coordination of electron-donating oxo ligand(s). Absorption spectra of [VOCl(tpa)]+ in acetonitrile showed a significant change upon addition of p-toluenesulfonic acid and HClO4, but not on addition of benzoic acid. Protonation at the oxo ligand by the former two acids is suggested. Cyclic voltammetric studies in acetonitrile verified the proton-coupled redox behavior of the V(III)/V(IV) process involving the oxo ligand for the first time. From the dependence of the added p-toluenesulfonic acid to the CV, redox potentials for the following species have been estimated: [V(IV)OCl(tpa)]+/[V(III)OCl(tpa)](E1/2=-1.59 V vs. Fc+/Fc), [V(IV)(OH)Cl(tpa)]2+/[V(III)(OH)Cl(tpa)]+(Epc=-1.34 V), [V(IV)(OH2)Cl(tpa)]3+/[V(III)(OH2)Cl(tpa)]2+(Epa=-0.49 V), and [V(IV)Cl2(tpa)]2+/[V(III)Cl2(tpa)]+(E1/2=-0.89 V). The reduction of [V(V)(O)2(tpa)]+ in 0.05 M [(n-Bu)4N]PF6 acetonitrile showed a major irreversible reduction wave V(V)/(IV) at -1.48 V. The metal reduction potentials of the oxovanadium(IV) and dioxovanadium(V) species are very close, reinforcing the significant influence of the oxo ligand(s).

Selektive Bildung von Aceton durch elektrochemische Reduktion von CO2, katalysiert durch einen Ru-Naphthyridin-Komplex

Die potentiostatische Elektrolyse von [Ru(bpy)(napy)2(CO)2](BF4)21 (bpy=2,2′-Bipyridin; napy=1,8-Naphthyridin) in Gegenwart von LiBF4 in CO2-gesattigtem DMSO bei −1.65 V (gegen Ag/Ag+) fuhrt zur Bildung von CO und Li2CO3 [Gl. (a)], wahrend in Gegenwart von (CH3)4NBF4 Aceton, (CH3)3N und {(CH3)4N}2CO3 gebildet werden [Gl. (b)] – dies ist die erste nahezu selektive Bildung von Aceton durch elektrochemische Reduktion von CO2. Die Selektivitat ist der Unterdruckung der reduktiven Spaltung der Ru-C(O)-Bindung von 1 entsprechend einem Angriff des freien napy-N-Atoms am Carbonyl-C-Atom zuzuschreiben.