UV-vis Electronic Absorption Spectra Research Articles

The static and frequency‐dependent second‐ and third‐order nonlinear optical properties of Zn(II) and Ni(II) complexes of 4‐methoxypyridine‐2‐carboxylic acid: A detailed experimental and theoretical study

Novel Zn(II) and Ni(II) complexes, [Zn(MeOPic)2(H2O)2] and [Ni(MeOPic)2(H2O)2] (MeOHPic = 4‐methoxypyridine‐2‐carboxylic acid [4meOHPic]), have been prepared and characterized by X‐ray diffraction (XRD), Fourier transform infrared (FTIR), and ultraviolet–visible (UV–Vis) techniques. Crystal structure analysis demonstrated that the 4meOHPic ligand is coordinated as a two‐dentate ligand through N and O atoms to central metal ions, and both of the complexes have distorted octahedral coordination geometry. The DFT‐B3LYP/6‐311++G(d,p)/LanL2DZ level was executed to perform DFT calculations for the Zn(II) complex with singlet spin state and the Ni(II) complex with triplet spin state. The UV–Vis electronic absorption spectra and natural bonding orbital (NBO) analyses also demonstrated that ligand–ligand and metal–ligand charge transfer interactions occur in Zn(II) and Ni(II) complexes. However, static and frequency‐dependent first‐order hyperpolarizability (β) parameters were found to be low because of the centrosymmetric crystal structures. As for the second‐order hyperpolarizabilities, the quadratic electro‐optical Kerr effect γ (−ω;ω,0,0) and electric field induced second harmonic generation γ (−2ω;ω,ω,0) parameters were calculated as 13.04 × 10−36 and 2258.9 × 10−36 esu for Ni(II) complex. Accordingly, it was demonstrated that Ni(II) complex is a potential candidate for third‐order nonlinear optical (NLO) materials.

Self-assembled gold nanoparticles on the serpentine networks of Calf Thymus-DNA Langmuir-Blodgett films as efficient SERS sensing platform: Fabrication and its application in thiram detection

Fabrication of efficient SERS active substrates from the Langmuir-Blodgett (LB) films of Calf Thymus-DNA (CT-DNA) molecule after incubation into gold nanocolloid for 24 h has been presented. Relaxation kinetics of CT-DNA molecules at the air-water interface has been explicitly studied. The experimental observations from UV–Vis electronic absorption spectra together with the FESEM and AFM images of CT-DNA molecule organized in LB film collectively suggest the presence of H-type aggregated domains due to plane-to-plane self-association of the CT-DNA molecules on the surface of the LB film. XPS spectrum of the as prepared substrate has been unveiled to identify its chemical compositions while their morphological features are explored from the FESEM and AFM images. The SERS efficacy of the substrate has been tested with the 4-Mercaptopyridine (4-MPy) molecule at trace concentration. SERS enhancement factors ranging from 106–107 orders of magnitude have been evaluated for the characteristic bands of the 4-MPy molecule. The substrate not only exhibits appreciable spectral reproducibility, but it also confirms its stability and uniformity. The as prepared SERS active substrate has also been used for thiram detection at ultrasensitive concentration.

Fabrication of gold nanoparticles tethered in heat-cooled calf thymus-deoxyribonucleic acid Langmuir-Blodgett film as effective surface-enhanced Raman scattering sensing platform

SERS active substrate fabricated through self-assembly of Gold nanoparticles on the disjointed networks of Heat-cooled Calf Thymus DNA (HC-Ct DNA) Langmuir-Blodgett (LB) film has been reported. Adsorption kinetics of HC-Ct DNA molecules at the air-water interface has been studied explicitly. The UV-Vis electronic absorption spectra in conjunction with the FESEM images collectively suggest the presence of H- type aggregated domains most likely owing to plane-to-plane self-association of the HC-Ct DNA molecules aligned vertically on the surface of the LB film. Elemental composition and the morphological features of the as-prepared substrate (APS) are explored from XPS analysis and the FESEM, AFM images respectively. The SERS efficacy of the APS has been tested with trace concentrations of 4-Mercaptopyridine molecule. Finally, this SERS active substrate has also been used for the detection of malathion at ultrasensitive concentrations.

The excited state behavior of Group IA alkaline-metal phthalocyanines revealed by photoluminescence and singlet oxygen formation

Group IA alkaline-metal phthalocyanine (Pc) complexes (Li2Pc, Na2Pc, K2Pc, Rb2Pc, Cs2Pc) have been synthesized and purified to study their excited state behavior. Their UV–Vis electronic absorption spectra, fluorescence emission and excitation spectra, fluorescence quantum yields and lifetimes, as well as singlet oxygen formation quantum yields have been measured in DMF. These photophysical properties are compared with that of H2Pc. The fluorescence and singlet oxygen formation properties reveal that alkaline metal Pcs show weak heavy atom effect. The results also reveal that alkaline-metal Pcs (Na2Pc, K2Pc, Rb2Pc, and Cs2Pc) show very different excited singlet state (S1) behavior from that of Li2PC and H2Pc. While S1 decay of Li2PC is mainly via intersystem crossing and fluorescence, the S1 decay of M2Pc (M = Na, K, Rb, Cs) is mainly metal ion dissociation: M2Pc(S1) → 2 M+ + [Pc]2−(S1), in addition to the intersystem crossing.

Weak Intrinsic Luminescence in Monomeric Proteins Arising from Charge Recombination

We had earlier reported on the presence of broad UV-Vis electronic absorption spectra (250—800 nm) in monomeric proteins rich in charged amino acids referred as Protein Charge Transfer Spectra or ProCharTS (Chem. Sci., 2017, 8, 5416). These spectra originate from charge transfer among charged amino acids. Specifically, photoinduced electron transfer was shown to occur from anionic Glutamate headgroup to the protein backbone/cationic Lysine headgroup OR from the protein backbone to cationic Lysine headgroup.

Anion-π Architectures of HAT(CN)6 and 5d Polycyanidometalates: [W(CN)8]3–, [Re(CN)7]3–, and [Pt(CN)6]2–

Homoleptic polycyanido-complexes of 5d metal ions with high coordination numbers (C.N.), 8 for [W(CN)8]3–, 7 for [Re(CN)7]3–, and 6 for [Pt(CN)6]2–, are found to form supramolecular anion-π chains with the multisite anion receptor HAT(CN)6 (hexaazatriphenylenehexacarbonitrile). The chains adopt a zigzag topology in the case of (XPh4)3[W(CN)8]·HAT(CN)6 (X = P: 1, X = As: 2) and (PPh4)3[Re(CN)7]·HAT(CN)6 (3), and a linear arrangement in the case of (PPh4)2[Pt(CN)6]·HAT(CN)6·0.5CH3CN·2Et2O (4). The anion-π interactions consist of 3-fold {M–C≡N–···δ+centroidpyrazine,ring}3 or single {M–C≡N–···δ+centroidpyrazine,C–C bond} intermolecular contacts with separation distances in the range of 2.79–3.20 A. An M-(CN)− → HAT(CN)6 charge transfer (CT) along these anion-π contacts is evidenced in the solid state by the appearance of new absorptions in the visible range of UV–vis electronic absorption spectra, as compared to the starting materials, and by dispersion-corrected density functional theory studies. The CT anio...

Preparation and Photoelectronic and Electrochemical Properties of Oligo[(1,1‐diisopropyl‐3,4‐diphenyl‐2,5‐silolene)‐co‐(alkylphenylsilylene)

We oligomerized 2,5‐dibromo‐1,1‐diisopropyl‐3,4‐diphenyl‐2,5‐silole with dichloroalkylphenylsilanes utilizing n‐BuLi to yield conjugated oligo[(1,1‐diisopropyl‐3,4‐diphenyl‐2,5‐silolene)‐co‐(alkylphenylsilylene)]s. Gel permeation chromatography measurements confirm that the synthesized materials are oligomeric. In addition, the prepared oligomers show characteristic diene stretching bands at 1579–1599 cm−1 in their FT‐IR spectra. Furthermore, the oligomers are highly soluble in common organic solvents such as tetrahydrofuran and chloroform. In tetrahydrofuran, the oligomers show strong maximum electronic absorption bands at 253–292 nm with molar absorptivities of 1.61 × 102 to 2.57 × 104 /cm M in their UV–vis electronic absorption spectra, indicating that the maxima are red‐shifted by 5–8 nm compared to the 2,5‐dibromo‐1,1‐diisopropyl‐3,4‐diphenyl‐2,5‐silole monomer, strong maximum electronic excitation bands at 292–312 nm, and strong maxima electronic emission bands at 385–396 nm in the emission fluorescence spectra. The emission and absorption spectra strongly suggest that the prepared silole‐containing oligomers may be conjugated through the oligomer backbone. In particular, cyclic voltammetry measurements of oligo[(1,1‐diisopropyl‐3,4‐diphenyl‐2,5‐silolene)‐co‐(diphenylsilylene)] deposited on a glassy carbon electrode in 1.0 M aqueous hydrogen chloride show two oxidation potentials at 0.98 and 1.61 V vs. Ag/Ag+, and two reduction potentials at 0.00 and −1.93 V vs. Ag/Ag+. The oligomers were stable on heating to 200 °C under nitrogen, as determined by thermogravimetric analysis, losing between 4% and 23% of their starting weights.

Synthesis of novel anthraquinones: Molecular structure, molecular chemical reactivity descriptors and interactions with DNA as antibiotic and anti-cancer drugs

Anthraquinones are well-known anticancer drugs. Anthraquinones anticancer drugs carry out their cytotoxic activities through their interaction with DNA, and inhibition of topoisomerase II activity. Anthraquinones (AQ5 and AQ5H) were synthesized and studied with 1,5-DAAQ by computational and experimental tools. The purpose of this study is to shade more light on mechanism of interaction between anthraquinone DNA affinic agents and different types of DNA. This study will lead to gain of information useful for drug design and development. Molecular structures were optimized using DFT B3LYP/6-31 + G(d). Depending on intramolecular hydrogen bonding interactions four conformers of AQ5 were detected within the range of about 42 kcal/mol. Molecular reactivity of the anthraquinone compounds was explored using global and condensed descriptors (electrophilicity and Fukui functions). NMR and UV–VIS electronic absorption spectra of anthraquinones/DNA were investigated at the physiological pH. The interaction of the anthraquinones (AQ5 and AQ5H) were studied with different DNA namely, calf thymus DNA, (Poly[dA].Poly[dT]) and (Poly[dG].Poly[dC]). UV–VIS electronic absorption spectral data were employed to measure the affinity constants of drug/DNA binding using Scatchard analysis. NMR study confirms qualitatively the drug/DNA interaction in terms of peak shift and broadening.

Octa-BODIPY derivative dendrimeric cyclotetraphosphazenes; photophysical properties and fluorescent chemosensor for Co2 + ions

We have designed and synthesized the first examples of fluorescent chemosensors based on octa-BODIPY decorated dendrimeric cyclotetraphosphazenes. The structures these synthesized compounds were verified by 1H, 13C, 31P NMR spectroscopies and UV–vis electronic absorption spectra. The photophysical and metal sensing properties in THF solutions of dendrimeric cyclotetraphosphazenes (OBCP 1–3) were investigated by fluorescence spectroscopy. OBCP 1–3 showed strong absorption in the 500–640nm region with high molar extinction coefficients. Additionally, octa-BODIPY decorated dendrimeric cyclotetraphosphazenes are candidate for fluorescent chemosensor for Co2+ showing high selectivity with a low limit of detection.

Interaction of anthraquinone anti-cancer drugs with DNA:Experimental and computational quantum chemical study

Anthraquinones form the basis of several anticancer drugs. Anthraquinones anticancer drugs carry out their cytotoxic activities through their interaction with DNA, and inhibition of topoisomerase II activity. Anthraquinones (AQ4 and AQ4H) were synthesized and studied along with 1,4-DAAQ by computational and experimental tools. The purpose of this study is to shade more light on mechanism of interaction between anthraquinone DNA affinic agents and different types of DNA. This study will lead to gain of information useful for drug design and development. Molecular structures were optimized using DFT B3LYP/6-31 + G(d). Depending on intramolecular hydrogen bonding interactions two conformers of AQ4 were detected and computed as 25.667 kcal/mol apart. Molecular reactivity of the anthraquinone compounds was explored using global and condensed descriptors (electrophilicity and Fukui functions). Molecular docking studies for the inhibition of CDK2 and DNA binding were carried out to explore the anti cancer potency of these drugs. NMR and UV-VIS electronic absorption spectra of anthraquinones/DNA were investigated at the physiological pH. The interaction of the three anthraquinones (AQ4, AQ4H and 1,4-DAAQ) were studied with three DNA (calf thymus DNA, (Poly[dA].Poly[dT]) and (Poly[dG].Poly[dC]). NMR study shows a qualitative pattern of drug/DNA interaction in terms of band shift and broadening. UV-VIS electronic absorption spectra were employed to measure the affinity constants of drug/DNA binding using Scatchard analysis.

Structure and Spectroscopy of o-anisidine Investigated by Density Functional Theory in Comparison with Experiments

The molecular structures, vibrational spectra (IR and Raman), UV-Vis electronic absorption spectra, and NMR spectra (13C and 1H) of o-anisidine have been investigated in terms of density functional theory by using B3LYP as a density functional and 6-311++G** as a basis set. Two stable and virtually degenerate conformers arising from non-planarity of the amino group of o-anisidine have been located at the room temperature. All normal modes of o-anisidine have been assigned in terms of percent contributions of the internal motions. All main electronic transitions in the UV-Vis spectrum of o-anisidine have been assigned. Solution that increases ionization potential of o-anisidine but decreases its electron affinity has been shown to affect the unoccupied orbitals of o-anisidine drastically, which shift all electronic absorption bands to longer wavelengths. The frontier molecular orbital, molecular electrostatic potential map, and atomic charge (Mulliken, ESP, and NBO) analyses have been shown useful in estimating both global and atom-inmolecule characteristics of o-anisidine. The present chemical shift calculations allow certain assignments of the experimental 13C and 1H NMR signals of o-anisidine. The high correlations between the experimental and the present computational spectral data indicate that the computational route presented in this study can be extended for the spectroscopic calculations of analogous compounds.

Monofunctional amines substituted fluorenylidene bridged cyclotriphosphazenes: ‘Turn-off’ fluorescence chemosensors for Cu2+ and Fe3+ ions

In the present work, the reaction of 2,2,4,4-tetra(anilino)-6,6-dichlorocyclotriphosphazene (4) and 2,2,4,4-tetra(2-naphthylamino)-6,6-dichlorocyclotriphosphazene (5) with 4,4′-(9-fluorenylidene)diphenol, FDP, (6) and 4,4′-(9-fluorenylidene)dianiline FDA (7) were studied in THF and new aniline (8 and 9) and 2-naphthylamine (10 and 11) substituted FDP-bridged cyclotriphosphazenes and aniline (12) and 2-naphthylamine (13) substituted FDA-bridged cyclotriphosphazene derivatives were obtained. All newly synthesized monofunctional amines substituted fluorenylidene bridged cyclotriphosphazenes (8–13) were fully characterized by elemental analysis, 1H and 31P NMR spectroscopies, MALDI-TOF mass spectrometry and UV–Vis electronic absorption spectra. The florescence properties of the synthesized new compounds were studied. The chemosensory behavior of the compounds against to metal ions was also investigated. The obtained fluorenylidene bridged 2-naphthylamine substituted cyclotriphosphazenes (10, 11 and 13) showed fluorescence chemosensor behavior with high selectivity for Fe3+ and Cu2+ ions in the solution.

Effects of solvent polarity on the absorption and fluorescence spectra of chlorogenic acid and caffeic acid compounds: determination of the dipole moments.

The effects of solvent polarity on absorption and fluorescence spectra of biologically active compounds (chlorogenic acid (CGA) and caffeic acids (CA)) have been investigated. In both spectra pronounced solvatochromic effects were observed with shift of emission peaks larger than the corresponding UV-vis electronic absorption spectra. From solvatochromic theory the ground and excited-state dipole moments were determined experimentally and theoretically. The differences between the excited and ground state dipole moment determined by Bakhshiev, Kawski-Chamma-Viallet and Reichardt equations are quite similar. The ground and excited-state dipole moments were determined by theoretical quantum chemical calculation using density function theory (DFT) method (Gaussian 09) and were also similar to the experimental results. The HOMO-LUMO energy band gaps for CGA and CFA were calculated and found to be 4.1119 and 1.8732 eV respectively. The results also indicated the CGA molecule is more stable than that of CFA. It was also observed that in both compounds the excited state possesses a higher dipole moment than that of the ground state. This confirms that the excited state of the hydroxycinnamic compounds is more polarized than that of the ground state and therefore is more sensitive to the solvent.

Spectroscopic and semiempirical investigation of the structural features of hetarylazo-5-isoxazolones tautomerism

3-Methyl-4-hetarylazo-5-isoxazolones (I–IV) have been synthesized and investigated on the basis of Fourier transform infrared (FT-IR), UV–visible (UV–Vis), proton nuclear magnetic resonance (1H NMR) spectroscopic techniques and elemental analysis. The measured FT-IR and 1H NMR spectra together with the theoretical calculations (semiempirical) showed that the investigated compounds exist in the hydrazone-keto form in the solid state and chloroform. However, the measured UV–Vis electronic absorption spectra in solutions clarified that the hetarylazo-5-isoxazolone dyes possess equilibrium between hydrazone-keto and common anion forms depending upon the nature of the medium. Furthermore, these dyes display a broad absorption band in the visible region (between 370 and 435nm) which could be assigned to π–π∗ transition with a considerable intramolecular charge transfer (CT) character.

Synthesis, characterization and DNA interaction of new copper(II) complexes of Schiff base-aroylhydrazones bearing naphthalene ring

Two new copper(II) complexes with the condensation products of methyl 2-naphthyl ketone with 4-hydroxybenzohydrazide, 4-hydroxy-N′-[(1Z)-1-(naphthalen-2-yl)ethylidene]benzohydrazide [HL1] and (Z)-ethyl 2-(4-(2-(1-(naphthalen-2-yl)ethylidene)hydrazinecarbonyl)phenoxy)acetate (HL2) were synthesized and characterized by elemental analysis, infrared spectra, UV–Vis electronic absorption spectra, magnetic susceptibility measurements, TGA, powder XRD and SEM–EDS. The binding properties of the copper(II) complexes with calf thymus DNA were studied by using the absorption titration method. DNA cleavage activities of the synthesized copper complexes were examined by using agarose gel electrophoresis. The effect of complex concentration on the DNA cleavage reactions in the absence and presence of H2O2 was also investigated. The experimental results suggest that the copper complexes bind significantly to calf thymus DNA by both groove binding and intercalation modes and cleavage effectively pBR322 DNA. The mechanistic studies demonstrate that a hydrogen peroxide-derived species and singlet oxygen (1O2) are the active oxidative species for DNA cleavage.

Synthesis, characterization, crystal structure and theoretical approach of Cu(II) complex with 4-{(Z)-[(2-hydroxybenzoyl)hydrazono]methyl}benzoic acid

Abstract The metal complex of [CuL2]·2DMF (L = 4-{(Z)-[(2-hydroxybenzoyl)hydrazono]methyl}benzoic acid, DMF = N,N-dimethylformamide) (1) had been synthesized and characterized by spectral method(IR), UV–Vis electronic absorption spectra, fluorescence spectra, elemental analysis, electrochemistry, thermal analysis (TG, DTG) and single crystal X-ray diffraction techniques. In the complex, the ligands act as univalent anion bidentate and coordination takes place in the enol tautomeric form with the enolic oxygen and azomethine nitrogen atoms. Molecular geometry from X-ray experiment of the title compound in the ground-state has been compared using the density functional method (B3LYP) and LANL2DZ basis set. DFT calculations at B3LYP/LANL2DZ level of theory prove that the electronic spectra of CuL2·2DMF is attributed to intra-complex electronic transitions as well as π–π* electronic transitions. Also, Mulliken charge analysis, natural bond orbitals (NBO), Wiberg bond index and frontier molecular orbitals (FMO) were performed at B3LYP/LANL2DZ level of theory. In addition, complex 1 exhibits strong photoluminescent emission at room temperature. The electrochemical studies reveal that redox of Cu2+/Cu+ in the complex are quasi-reversible processes. The result of TG analysis shows that the title complex was stable under 100.0 °C.

ASYMMETRIC BIS(BIDENTATE) AZINE LIGAND AND TRANSITION METAL COMPLEXES: SYNTHESIS, CHARACTERIZATION, DNA-BINDING AND CLEAVAGE STUDIES AND EXTRACTION PROPERTIES FOR SELECTED METALS AND DICHROMATE ANIONS

New bis(bidentate) azine NNN’N’ donor ligand was prepared by linking (1Z,1’Z)-1,1’-{propane-1,3-diylbis[oxybenzene-4,1-diyl(1Z)eth-1-yl-1-ylidene]} dihydra-zine to pyridine-2-carbaldehyde. Two kinds of copper(II) and nickel(II) complexes with different stoichiometries were prepared. Reaction of bis(azine) ligand with Cu(II) and Ni(II) chloride with 1:1 molar ratio gave azine complexes with stoichiometry [M(L)Cl 2 ] while 2:1 molar ratio reaction of Cu(II) and Ni(II) chloride with bis(azine) composed binuclear copper complexes with general stoichiometry [M 2 (L)Cl 4 ]. The structures of both bis-azine ligand and its complexes were identified by elemental analysis, infrared spectra, UV–Vis electronic absorption spectra and magnetic susceptibility measurements, TGA and powder XRD. DNA binding and DNA cleavage activities of the synthesized metal complexes were examined by using UV-vis titration and agarose gel electrophoresis, respectively. The results indicate that all the complexes bind significantly calf thymus DNA and cleavage pBR322 DNA. Furthermore, the complexing properties of the bis-azine ligand toward selected transition metal cations and dichromate anions were also reported.

Synthesis and characterization of bis-acylhydrazone derivatives as tetradentate ligands and their dinuclear metal(II) complexes

Two novel bis-acylhydrazone where as 1,4-diacetylbenzene bis(4-hydroxy benzoyl hydrazone) H_2L^1 and 1,4-diacetylbenzene bis(4-nitrobenzoyl hydrazone) H_2L^2 ligands bearing two hydrazone side groups and their metal(II) complexes have been synthesized and characterized by ^1H-NMR^ 13 C-NMR, elemental analysis, FT-IR infrared spectra, magnetic susceptibility measurements and UV-vis electronic absorption spectra. The L_1H_2, L_2H_2) ligands were synthesized by reacting 4-hydroxybenzohydrazide and 4-nitrobenzohydrazide with 1,4-diacetylbenzene, respectively. The ligands H_2L^1, L_2H_2) react with metal(II) chlorides anhydrous to form polymeric dinuclear metal(II) complexes with general formula [(M_2(L_x)_2_n] with a metal to ligand ratio of 1:1 when [x = 1, 2; M = Ni(II), Co(II), Cu(II), Zn(II) and Cd(II)]. In the complexes, the ligands act as dianionic tetradentate and coordination takes place in the enol tautomeric form with the enolic oxygen and azomethine nitrogen atoms while the phenolic hydroxyl and nitro groups of dihyrazone moiety do not participate in coordination.

Novel homogeneous catalyst comprising ruthenium and trimethylphosphite for the hydrolysis of sodium borohydride

Homogeneous catalytic hydrolysis of sodium borohydride starting with Ru(acac) 3 (acac = acetylacetonate) and P(OMe) 3 was followed by monitoring the hydrogen evolution and the UV–vis electronic absorption spectra which shows the conversion of all ruthenium(III) to a ruthenium(II) species, most likely acting as catalyst. This active catalyst is alive only under reducing conditions and converted mainly to Ru(acac) 3 along with other minor complexes when the catalytic reaction is over. A ruthenium(II) complex was isolated from the reaction solution after the complete catalytic hydrolysis of sodium borohydride and characterized to be [Ru{P(OMe) 3} 4H 2] by single crystal XRD, MS, UV–vis, FTIR, 1H, 13C and 31P NMR spectroscopy. [Ru{P(OMe) 3} 4H 2] complex crystallizes in the triclinic space group P-1 with a = 10.066(2) Å, b = 19.108(3) Å, c = 20.938(4) Å, α = 78.839(14)°, β = 87.308(16)° and γ = 79.506(14)°. This ruthenium(II) complex was found not to be the active catalyst in the hydrolysis of sodium borohydride, rather one of its conversion products after catalysis. Although the active catalyst could not be isolated from the reaction solution, it could be stabilized by adding chelating 2,2′-bipyridine into the solution during the catalysis. Thus, a stabilized form of the active catalyst, [Ru(acac)(bipy){P(OMe) 3}H], could be isolated and characterized by MS, UV–vis, FTIR, 1H, 13C and 31P NMR spectroscopy. [Ru(acac)(bipy){P(OMe) 3}H] is expectedly not as active as the ruthenium(II) species formed in situ during the catalysis. Taking all the results together reveals that the active catalyst is a ruthenium(II) complex, either [Ru(acac){P(OMe) 3} 3H] or most likely its dissociation product, [Ru(acac){P(OMe) 3} 2H]. Control experiments showed that 2,2′-bipyridine can replace only the trimethylphosphite ligands but not the acetylacetonato ligand in the ruthenium(II) complex.

The syntheses and characterization of Os(II) and Ru(II)/Os(II) bimetallic complexes with dipyrido(2,3-a:3′,2′-j)phenazine (dpop′) and the bridging ligand 2,3,5,6-tetra(2-pyridyl)-pyrazine (tppz)

The syntheses of mixed ligand mono metallic [Os(dpop′)(tppz)](PF6)2, homo-bimetallic [(dpop′)Os(tppz)Os(dpop′)](PF6)4 and mixed metal bimetallic [(dpop′)Ru(tppz)Os(dpop′)](PF6)4 (dpop′=dipyrido(2,3-a:3′,2′-j)phenazine; tppz=2,3,5,6-tetra(2-pyridyl)-pyrazine) complexes is described. NMR spectroscopy was used to confirm pure products were separated from similar species. The 1H NMR spectrum for the mixed metal Ru/Os bimetallic complex ion reflects additive components of the Ru/Ru and Os/Os bimetallic species. Proton resonances on Ru(II) bonded ligands are upfield from Os(II) bonded ligands. Cyclic voltammetry for the Os/Os and Ru/Os bimetallic complex ions show the reversible tppz0/−1 reduction at less negative potential than the dpop′0/−1 reduction. Additionally, the [(dpop′)Os(tppz)Os(dpop′)]4+ ion displays reductive coupling of the remote terminal dpop′ ligands that is not observed in the bimetallic Ru/Ru species, indicating larger metal–ligand mixing occurs for Os(II) than Ru(II) complexes. The UV–Vis electronic absorption spectra for all complex ions show intense Os(dπ)→dpop′(π∗) and Os(dπ)→tppz(π∗) MLCT transitions in the visible spectrum with IL transitions in the UV.