Acid-Base Properties of the Ground and Excited States of Ruthenium(II) Bis(2,2'-bipyridine) 3-Carboxyl-2,2'-bipyridine

Acid-base properties for ruthenium(II) bis(2,2'-bipyridine) 3-carboxyl-2,2'-bipyridine reveal a ground state pK(a) of 0.82 +/- 0.07 and an excited state pK(a) of 2.31 +/- 0.05, a 1.5 pH unit increase from the ground state. The excited state pK(a) is temperature independent while the ground state pK(a)(0) increases with temperature and has DeltaH(0) and DeltaS(0) values of -990 +/- 149 cm(-)(1) and -4.57 +/- 0.48 cm(-)(1) K(-)(1), respectively. The acidic form of the complex emits at lower energy than the basic form at both 296 and 77 K. The emission energy maxima are solvent dependent and decrease in energy when the solvent changes from 4:1 (v/v) 2-MeTHF-CH(2)Cl(2) to water and when the pH decreases. Changes in excited state lifetimes with emission energy follow the energy gap law with an intercept of 49 +/- 1 and a slope of (2.11 +/- 0.09) x 10(-)(3). Emission quantum yields for protonated and deprotonated species in 4:1 (v/v) 2-MeTHF-CH(2)Cl(2) are 0.023 +/- 0.001 and 0.110 +/- 0.002, respectively. The temperature dependence of the emission lifetimes gives energy barriers of 270 cm(-)(1) for the complex in aqueous solution at pH -0.5, and 990 cm(-)(1) in aqueous solution at pH 4.5, and 1920 cm(-)(1) in 4:1 (v/v) 2-MeTHF-CH(2)Cl(2.)     

Molecular Orbital Calculation and Spectroscopic Study of the Photochemical Generation of Bis(2,2'-bipyridine)rhodium(I) from Bis(2,2'-bipyridine)(oxalato)rhodium(III)

A planar complex, [Rh(bpy)(2)](+) (bpy = 2,2'-bipyridine), was obtained from [Rh(ox)(bpy)(2)](+) (ox = oxalato) by photoirradiation. A rate constant k for the photoreaction was evaluated as 1 x 10(8) s(-1) in simple first-order kinetics, whereas a ligand dissociation, a reorganization of the coordinated bpy, and a two-electron transfer were involved in the reaction. The process of the Rh(I) complex generation was investigated in terms of a discrete variational (DV)-Xalpha molecular orbital calculation on [Rh(ox)(HN=CHCH=NH)(2)](+) instead of [Rh(ox)(bpy)(2)](+). From the calculation, using the transition-state method, it was predicted that a transition of the ox pi orbital to the metal 4d(z)()2 orbital caused the ligand dissociation and the reorganization of the coordinated bpy occurred in the ox pi to Rh 4d(x)()2(-y)2 excited state stabilized by the ox elimination. Upon release of the ligand and a change from octahedral to square-planar geometry, the electron density on the metal increased and the Rh 4d orbital acquired a d(8) electronic configuration.     

Spectral evidence and DFT calculations on the formation of Bis(2,2'-bipyridine)platinum(II)-N-base adducts

The formation of 1:1 adducts of Pt(bpy)2(2+) (bpy = 2,2'-bipyridine) with various N bases (B) has been ascertained in water at ambient temperature by spectrophotometric titration and electrospray ionization mass spectroscopy. A pseudo-five-coordinated complex, [Pt(bpy)2(B)](2+) with a monodentating bpy, is proposed based on density functional theory calculation. The formation constants (Kc) increase with the nucleophilicity of B except for sterically hindered N-bases, indicating an associative ligand-substitution mechanism.     

Time-resolved photoacoustics study of the ruthenium(II) bis(2,2'-bipyridine)(4,4'-dicarboxy-2,2'-bipyridine) complex

The formation and the decay of the triplet metal to ligand charge transfer state ((3)MLCT) of ruthenium(II) bis(2,2'-bipyridine)(4,4'-dicarboxy-2,2'-bipyridine) (Ru(bpy)(2)(dcbpy)) were characterized using photoacoustic calorimetry. At pH 6 and 2, the (3)MLCT state formation leads to a volume change of -8 mL mol(-1) and enthalpy changes of 17 kcal mol(-1) and 13 kcal mol(-1), respectively. We attribute the volume contraction to structural changes and to solvent electrostriction. At pH 4, the photoexcitation of the complex leads to an expansion of 14 mL mol(-1) and an enthalpy change of approximately 119 kcal mol(-1) due to protonation of the carboxyl group in the excited state.     

Synthesis of Ruthenium(II) Tris(2,2'-bipyridine) Complexes

A procedure for preparing Ru(II) tris(2,2'-bipyridine) complexes containing one functionalized bipyridine ligand was developed.     

Crystal Structure of Tris(2,2'-bipyridine)nickel(II) Tetrachlorozincate

1　INTRODUCTIONThe coordination chemistry oftransition metalcomplexeshasbecomeofremark able interestin recentyears.Sotoftetal.reported the structure of Ni( CH3CN) 6·Zn Cl4 〔1〕.Recently,Shyu etal.reported the structure of〔 Ni( bipy) 3〕〔 Fe( CN) 5 ( NO)〕· 3 H2 O〔2〕.Herein we reportthe structure oftitle complex〔 Ni( bipy) 3〕〔 Zn Cl4 〕 which issimilarto theformertwo complexes.Itisvery interesting to synthesizebimetallic compoundsfor both theoreticalstudy and practicalapp…     

NADH Electrooxidation Using Bis(1,10-phenanthroline-5,6-dione) (2,2'-bipyridine)ruthenium(II)-Exchanged Zirconium Phosphate Modified Carbon Paste Electrodes

We present a carbon paste electrode (CPE) modified using the electron mediator bis(1,10‐phenanthroline‐5,6‐dione)(2,2′‐bipyridine)ruthenium(II) ([Ru(phend)₂bpy]²⁺) exchanged into the inorganic layered material zirconium phosphate (ZrP). X‐Ray powder diffraction showed that the interlayer distance of ZrP increases upon [Ru(phend)₂bpy]²⁺ intercalation from 10.3 Å to 14.2 Å. The UV‐vis and IR spectroscopies results showed the characteristic peaks expected for [Ru(phend)₂bpy]²⁺. The UV‐vis spectrophotometric results indicate that the [Ru(phend)₂bpy]²⁺ concentration inside the ZrP layers increased as a function of the loading level. The exchanged [Ru(phend)₂bpy]²⁺ exhibited luminescence even at low concentration. Modified CPEs were constructed and analyzed using cyclic voltammetry. The intercalated mediator remained electroactive within the layers (E°′=–38.5 mV vs. Ag/AgCl, 3.5 M NaCl) and electrocatalysis of NADH oxidation was observed. The kinetics of the modified CPE shows a Michaelis–Menten behavior. This CPE was used for the oxidation of NADH in the presence of Bakers' yeast alcohol dehydrogenase. A calibration plot for ethanol is presented.