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Electronic transport through graphene magnetic barriers is studied theoretically in presence of an external time harmonic scalar potential in the framework of non-perturbative Landau–Floquet Formalism. The oscillating field mostly suppresses the transmission for rectangular magnetic barrier structure and exhibits the Fano resonance for multiphoton processes due to the presence of bound state inside the barrier. While, for a pair of delta function barriers of larger separation, the oscillating potential suppresses the usual Fabry–Perot oscillations in the transmission and a new type of asymmetric Fano resonance is noted for smaller separation, occurring due to extended states between the barriers. [ABSTRACT FROM AUTHOR]

Abstract: 1-Alkyl-2-{(o-thioalkyl)phenylazo}imidazole acts as imidazolyl-N donor ligand to Cd(II) although they have potential three donor centres namely N(imidazole), N(azo) and –SR. Two series of complexes [Cd(SRaaiNR/)2X2] (X=Cl, Br, I) and [Cd(SRaaiNR/)4](ClO4)2 are synthesized with these ligands. These complexes are spectroscopically (IR, UV–Vis, 1H NMR) characterised and, the single crystal X-ray structures of [Cd(SEtaaiNEt)2I2] and [Cd(SEtaaiNEt)4](ClO4)2 (where SEtaaiNEt=1-ethyl-2-{(o-thioalkyl)phenylazo}imidazole) have confirmed the distorted tetrahedral structures. The UV light irradiation in MeCN solution of the complexes shows E-to-Z (E and Z refer to trans and cis-configuration about –N, respectively) isomerisation of the coordinated azoimidazole. The rate of isomerisation follows the sequence : [Cd(SRaaiNR/)4](ClO4)2 <[Cd(SRaaiNR/)2Cl2]<[Cd(SRaaiNR/)2Br2]<[Cd(SRaaiNR/)2I2]. Quantum yields (ϕE → Z ) and the activation energy (E a) of the isomerisation of the complexes are lower than that of free ligand data. The observation has been explained considering the molecular association that increases the mass and rotor volume of the complexes. [Copyright &y& Elsevier]

Abstract: Halide bridging lead(II) coordination polymer of 1-alkyl-2-(arylazo)imidazole (RaaiR′), [Pb(RaaiR′)(μ-X)2] n is spectroscopically characterized and, the single crystal X-ray structure of [Pb(MeaaiMe)(μ-Cl)2] (where MeaaiMe=1-methyl-2-(p-tolylazo)imidazole) has confirmed the structure. The UV light irradiation in DMF solution of the complexes shows E-to-Z (E and Z refer to trans and cis-configuration about –N, respectively) isomerization of the coordinated azoimidazole. The rate of isomerization follows: [Pb(RaaiR′)(μ-Cl)2] n <[Pb(RaaiR′)(μ-Br)2] n <[Pb(RaaiR′)(μ-I)2] n . Quantum yields (ϕ E→Z) and the activation energy (E a) of the isomerization of the complexes are lower than that of free ligand data. These may be due to increased mass and rotor volume of the complexes. The results are supported by DFT computation of optimized structures. [Copyright &y& Elsevier]

The influence of Al concentration on the current density in GaAs-AlGaAs heterostructure is studied for two different classes of the Generalized Thue-Morse superlattice (GTS): (i) width-barrier GTS and (ii) height-barrier GTS. The occurrence of resonances in the transmission is found to be highly dependent on the Al concentration as well as on the degree of quasi-periodicity of the system. Interesting features are noted for the current density profile with the increase in the Al content for the width-barrier case. The use of the height-barrier GTS with small Al content could be suggested to achieve the negative differential conducting regimes at comparatively low applied bias. The effects of the applied field as well as of the quasi-periodicity on the carrier localization are also studied. [ABSTRACT FROM AUTHOR]

Abstract: Reaction of Cu(ClO4)2·6H2O, SRaaiNR′ (1-alkyl-2-[(o-thioalkyl)phenylazo]imidazole) and NH4SCN (1:1:2mol ratio) affords distorted square pyramidal, [CuII(SRaaiNR′)(SCN)2] (3) compound while identical reaction with [Cu(MeCN)4](ClO4) yields –SCN– bridged coordination polymer, [CuI(SRaaiNR′)(SCN)] n (4). These two redox states [CuII and CuI] are interconvertible; reduction of [CuII(SRaaiNR′)(SCN)2] by ascorbic acid yields [CuI(SRaaiNR′)(SCN)] n while the oxidation of [CuI(SRaaiNR′)(SCN)] n by H2O2 in presence of excess NH4SCN affords [CuII(SRaaiNR′)(SCN)2]. They are structurally confirmed by single crystal X-ray diffraction study. Cyclic voltammogram of the complexes show Cu(II)/Cu(I) redox couple at ∼0.4V and azo reductions at negative to SCE. UV light irradiation in MeCN solution of [CuI(SRaaiNR′)(SCN)] n (4) show trans-to-cis isomerisation of coordinated azoimidazole. The reverse transformation, cis-to-trans, is very slow with visible light irradiation while the process is thermally accessible. Quantum yields (ϕ t→c) of trans-to-cis isomerisation are calculated and free ligands show higher ϕ than their Cu(I) complexes. The activation energy (E a) of cis-to-trans isomerisation is calculated by controlled temperature experiment. Copper(II) complexes, 3, do not show photochromism. DFT and TDDFT calculation of representative complexes have been used to determine the composition and energy of molecular levels and results have been used to explain the solution spectra, photochromism and redox properties of the complexes. [ABSTRACT FROM AUTHOR]

Abstract: Protonation or dialkylation of 2-(arylazo)imidazoles (RaaiH) has generated azoimidazolium motif (RaaiH2 +, RaaiR′H+, RaaiR′ 2 + where R=H, CH3 and R′ =Me, Et, –CH2Ph). Electrostatic attraction between imdazolium cation and counter ions like Cl−, , has generated hydrogen bonded azoimidazolium-chloride/chlorometallated networks. The single crystal X-ray structure of 1-benzyl-2-(phenylazo)imidazolium chloride shows tape like 1-D network of [Cl(H2O)4]−. Aquated Cl− forms 10 membered supracycle through hydrogen bonding with imidazolium ion. The X-ray structures of [HaaiMe2 (1,3)]+[Me2NH2]+ [ZnCl4]2− and [MeaaiH2 +·H2O]2[PtCl6]2− show hydrogen bonded chlorometallate chain penetrated into the channel developed by organic motif. Azoimidazolium units are associated through π···π and C–H···π interactions to strengthen the supramolecular geometry. [Copyright &y& Elsevier]

Abstract: The reaction of CuX (X=Cl, Br, I) with a mixture of PPh3 and 1-alkyl-2-(naphthyl-α/β-azo)imidazole has synthesized mixed ligand complexes of the composition, [Cu(α/β-NaiR)(PPh3)X]. The spectroscopic characterization (IR, UV–Vis, 1H NMR) supports this formulation. The single crystal X-ray diffraction study of [Cu((α-NaiMe)(PPh3)I] (7a) (α-NaiMe=1-methyl-2-(naphthyl-α-azo)imidazole) shows a distorted tetrahedral geometry about Cu(I). Cyclic voltammograms of the complexes show a high potential Cu(II)/Cu(I) couple and azo reductions. The [Cu(α/β-NaiR)(PPh3)I] complexes show an additional oxidative response at 0.4V that is assigned to I/I− A sharp anodic peak at ∼−0.2V is assigned to the oxidation of metallic Cu, deposited on electrode surface upon scanning to the negative side of the SCE. DFT and TD-DFT computations of [Cu((α-NaiMe)(PPh3)I] (7a), [Cu((α-NaiMe)(PPh3)I]+ (7a+ ) and [Cu((α-NaiMe)(PPh3)I]− (7a− ) were carried out to examine the electronic configuration and to explain the spectral and redox properties of the complexes. [Copyright &y& Elsevier]

Abstract: The reaction of Pd(β-NaiR)Cl2 (2) [β-NaiR (1)=1-alkyl-2-(naphthyl-β-azo)imidazoles] with ArNH2 in MeCN has yielded a C–N coupled product chloro[1-alkyl-2-{(7-imidoaryl)naphthyl-β-azo}imidazole-N,N′,N′′]palladium(II), Pd(β-NaiR–N–Ar)Cl (3–5) and coupling takes place at ortho-C–H position of pendant naphthyl group. The structural confirmation has been achieved by single crystal X-ray structure determination of the representative complexes, Pd(β-NaiEt)Cl2 (2b) and Pd(β-NaiEt–N–C6H4–Cl-p)Cl (5b). The electronic spectra of the products, 3–5, exhibit characteristic transition within 600–900nm those are absent in Pd(β-NaiR)Cl2 (2). Cyclic voltammogram shows one oxidative response and two ligand reductions. The products are emissive. The excited state decays via radiative and non-radiative biexponential routes. The electronic structure, spectra and redox properties are explained by DFT computation. [Copyright &y& Elsevier]

Abstract: The complexes, cis-(CO)-trans-(Cl)-[Ru(SRaaiNR)(CO)2Cl2] (2) and trans-(Cl)-[Ru(SRaaiNR)(CO)Cl2] (3) (SRaaiNR=1-alkyl-2-{(o-thioalkyl)phenylazo}imidazoles; R=Me (1a) and Et (1b)) have been synthesized and characterized. The structural confirmation is achieved by single crystal X-ray structure determinations. The complexes show Ru(III)/Ru(II) couple and ligand reductions. Electronic structure and spectral properties of the complexes have been explained with the DFT and TDDFT calculation. [Copyright &y& Elsevier]

Abstract: 1,3-Di-alkyl-2-(arylazo)imidazolium iodide () has been used to prepare iodocuprate(I) and iodoargentate(I) complexes. The structural confirmation has been carried out by single crystal X-ray diffraction study in representative cases. Iodo bridged anion, [Cu2(μ-I)2I2]2−, serves as charge support to dialkylazoimidazolium ion (). Silver(I) compound is a trimeric iodo-bridged [Ag3I5]2− that forms 1D chain while imidazolium ion, , is penetrating into the network. Electrostatic interaction between organic cation and inorganic anion and supramolecular interactions viz. hydrogen bonding, D–H–π, π–π interactions contribute to the crystal packing. [Copyright &y& Elsevier]

Abstract: 1-Alkyl-2-{(o-thioalkyl)phenylazo}imidazole (SRaaiNR/, 1) reacts with Co(ClO4)2·6H2O to form [Co(SRaaiNR/)2](ClO4)2 (2). The single crystal X-ray structure of one of the complexes of 2 shows a tridentate chelation N(imidazole), N(azo), S(thioether) system. In the structure one of ClO4 − anions shows disorder and forms an (imidazole)C–H···O(ClO3) interaction leading to a 1-D chain. Co(OAc)2.4H2O and SRaaiNR/ react in the presence of NH4SCN (1:1:2 mole ratio) in methanol and the complex [Co(SRaaiNR/)2(SCN)2] (3) has been separated. The single crystal X-ray structure determination has established the structure of the complexes in which the ligand SRaaiNR/ acts in a bidentate N(imidazole), N(azo) chelation mode. A cyclic voltammogram shows a Co(III)/Co(II) oxidative response at 0.6–0.8V and azo reductions. DFT computation using optimized geometry support the electronic spectral and redox properties of the complexes. [Copyright &y& Elsevier]

Abstract: The reaction of 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazoles (SRaaiNR) (2a/2b) with Ru(II) has synthesized [Ru(SRaaiNR)2](ClO4)2 (3a/3b) in 2-methoxyethanol. The reaction in methanol, however, has synthesized [Ru(SRaaiNR)( S RaaiNR)Cl](ClO4) (4a/4b). The solid phase reaction of SRaaiNR and RuCl3 on silica gel surface upon microwave irradiation has synthesized [Ru(SRaaiNR)(SaaiNR)](PF6) (5a/5b) [SRaaiNR represents tridentate N,N′,S-chelator; S RaaiNR is N,N′-bidentate chelator where S does not coordinate and SaaiNR refers N,N′,S-chelator where S refers to thiolato binding]. The structural characterization of [Ru(SEtaaiNEt)( S EtaaiNEt)Cl](ClO4) (4b) and [Ru(SEtaaiNEt)(SaaiNEt)](PF6) (5b) has been confirmed by single crystal X-ray diffraction study. The IR, UV–Vis, and 1H NMR spectral data also support the stereochemistry of the complexes. The complexes show metal oxidation, Ru(III)/Ru(II), and ligand reductions (azo/azo−, azo−/azo ). The molecular orbital diagram has been drawn by density functional theory (DFT) calculation. Normal mode of analysis has been performed to correlate calculated and experimental frequencies of representative complexes. The electronic movement and assignment of electronic spectra have been carried out by TDDFT calculation both in gas and acetonitrile phase. [Copyright &y& Elsevier]

Reaction between PdCI[sub2] and 1-alkyl-2-(arylazo)imidazole (RaaiR') or 1-aIkyl-2-(naphthyl-α/β-azo)imidazole (α/β- NaiR') under ref lux in ethanol has isolated complexes of compositions Pd(RaaiR')[sub2]Cl[sub2] (5, 6) and Pd(czlfl-NaiR')[sub2]Cl[sub2] (7, 8). The X-ray structure determination of one of the molecules, Pd(α-NaiBz)[sub2]Cl[sub2] (7c), has reported a trans-PdCI[sub2] configuration, and a-NaiBz acts as monodentate N(imidazole) donor ligand. The spectral (IR, UV-vis, [sup1]H NMR) data support the structure. UV light irradiation (light source: Perkin-Elmer LS 55 spectrofluorimeter, Xenon discharge lamp, λ = 360-396 nm) in a MeCN solution of the complexes shows E-to-Z isomerization of the coordinated azoimidazole unit. The reverse transformation, Z-to-E, is very slow with visible light irradiation. Quantum yields (ϕ[subE→z]) of E-to-Zisomerization are calculated, and ϕ is lower than that of the free ligand but comparable with those of Cd(ll) and Hg(ll) complexes of the same ligand. The Z-to-E isomerization is a thermally induced process. The activation energy (Ea) of Z-to-E isomerization is calculated by controlled-temperature experimentation. cis- Pd(azoimidazole)Cl[sub2] complexes (azomidazole acts as N(imidazole) and N(azo) chelating ligand) do not respond upon light irradiation, which supports the idea that the presence of noncoordinated azo-N to make free azo (-NN-) function is important to reveal photochromic activity. DFT calculation of Pd(α-NaiBz)[sub2]Cl[sub2] (7c) has suggested that the HOMO of the molecule is constituted of Pd (32%) and Cl (66%), and hence photo excitation may use the energy of Pd and Cl instead of that of the photofunctional —NN℄Ar motif; thus, the rate of photoisomerization and quantum yield decrease versus the free ligand values. [ABSTRACT FROM AUTHOR]

Reaction of Ni(ClO4)2 · 6H2O with 1-alkyl-2-(arylazo)imidazole (RaaiR/) and sodium azide (NaN3) or ammonium thiocyanate (NH4SCN) (1 : 2 : 2 molar ratio) in methanol gives [Ni(RaaiR/)2(X)2] (X=N3 (3, 4) and SCN (5, 6). All these complexes are characterized by elemental analyses, UV-Vis and IR spectral data, thermal and magnetic moment measurements. The X-ray structure is confirmed by single crystal measurement of [Ni(Pai-Me)2(N3)2] (3a). Cyclic voltammetry exhibits quasireversible response at >0.80 V corresponding to Ni(III)/Ni(II) couple along with ligand reductions at negative potential (<-0.5 V) to SCE reference. The electronic structure, spectral and redox properties are explained by DFT (Gaussian03) calculation. [ABSTRACT FROM AUTHOR]

Abstract: [Ni(NaiR)2(X)2] (X=N3 (3, 4) and NCS (5, 6) complexes are synthesized from the reaction of Ni(ClO4)2 ·6H2O with 1-alkyl-2-(naphthyl-α/β-azo)imidazole (α/β-NaiR) and sodium azide (NaN3) or ammonium thiocyanate (NH4NCS) (1:2:2 molar ratio) in methanol solution. The complexes are characterized by elemental, spectroscopic and magnetic study. The distorted octahedral structure has been confirmed by single crystal X-ray diffraction study of [Ni(β-NaiEt)2(NCS)2] (6b). Cyclic voltammogram exhibits quasireversible oxidation response at 0.3–0.4V which is corresponding to Ni(III)/Ni(II) couple along with ligand reductions at negative potential to SCE reference electrode. [Copyright &y& Elsevier]

Abstract: trans-(Cl)-[Ru(CO)2Cl2(PaiR/TaiR)] compounds have been synthesized by reacting 1-alkyl-2-(phenylazo)imidazole (PaiR) or 1-alkyl-2-(p-tolylazo)imidazoles (TaiR) with [Ru(CO)2Cl2] n in methanol under refluxing conditions. The X-ray crystallographic study of trans-(Cl)-[Ru(CO)2Cl2(PaiEt)] (PaiEt=1-ethyl-2-(phenylazo)imidazole) shows a distorted octahedral geometry with a trans-Cl,Cl configuration. An intermolecular hydrogen bonded dimer serves as a motif in the supramolecular network with C–H⋯π and π⋯π interactions. The complexes show metal oxidation, Ru(III)/Ru(II); and reduction of the coordinated azo (–N) function. The molecular orbital diagram has been drawn by density functional theory (DFT) using an optimized geometry from the single crystal X-ray parameters. The electronic movement and assignment of electronic spectra have been carried out by TD-DFT calculations both in the gas and acetonitrile phase. [Copyright &y& Elsevier]

A one channel distorted wave approximation has been used to calculate the ionization cross section for the 3s electron of Na atom by alpha particle impact. For a consistency check we have also run the standard CDW-EIS code of McSherry et al. [Comput. Phys. Commun. 155, 144 (2003)] and found reasonable agreement in the high energy region among the present results, the CDW-EIS results and the classical trajectory Monte Carlo (CTMC) calculations. It is also found that the present results tend to agree qualitatively with the low energy measurement of Knoop et al. [J. Phys. B 38, 1987 (2005)] at as low as 10 keV amu-1, although the present theoretical approach is expected to be suitable in the high energy area. This qualitative agreement in the low energy region is attributed to the partially correlated ground state wave function used in the present calculation. [ABSTRACT FROM AUTHOR]

Abstract: Manganese(II)-naphthylazoimidazole complexes using and NCS− as counter ions are characterized as Mn(β-NaiR)2(X)2(β-NaiEt=1-alkyl-2-(naphthyl-β-azo)imidazole; , NCS−). The ligands are unsymmetric N(imidazole), N(azo) chelating agents. The microanalytical, spectral (FT-IR, UV–vis), magnetic (bulk moment and EPR) and electrochemical data establish the structure and composition of the complexes. The single crystal X-ray diffraction studies of Mn(β-NaiEt)2(N3)2 and Mn(β-NaiEt)2(NCS)2(β-NaiEt=1-ethyl-2-(naphthyl-β-azo)imidazole) have confirmed the three dimensional structure of the complexes. Cyclic voltammetry exhibits high potential Mn(III)/Mn(II) couple along with azo reductions. The EPR spectra show usual pattern. [Copyright &y& Elsevier]

Reaction between CdX2 and 1-alkyl-2-(phenylazo)imidazole (RaaiR′) has isolated complexes of composition Cd-(RaaiR′)2X2 in MeOH or MeCN. Crystallization of Cd(RaaiR′)2I2 from N,N-dimethylformamide (DMF) has separated [Cd(RaaiR′)I2·DMF], while Cd(RaaiR′)2X2 (X = Cl and Br) remains unchanged in its composition upon crystallization under identical conditions. The structure has been established by spectral (UV-vis and 1H NMR) data and confirmation in the latter case by a single-crystal X-ray diffraction study of [Cd(TaiMe)I2-DMF] [where TaiMe = 1-methyl-2-(p-tolylazo)imidazole]. UV-light irradiation in a MeCN solution of Cd(RaaiR′)2I2 and [Cd(RaaiR′)I2·DMF] shows trans-to-cis isomerization of coordinated azoimidazole. The reverse transformation, cis-to-trans, is very slow with visible light irradiation. Quantum yields (Φt-c) of trans-to-cis isomerization are calculated, and the free ligand shows higher Φ values than their cadmium(Il) iodo complexes. The cis-to-trans isomerization is a thermally induced process. The activation energy (Ea) of cis-to-trans isomerization is calculated by a controlled-temperature experiment. The effects of the anions (Cl-, Br-, I-, and CIO4-) and the number of coordinated azoimidazoles (RaaiR′) [Cd(RaaiR′) or Cd(RaaiR′)2) on the rate and quantum yields of photochromism are established in this work. A slow rate of photoisomerization of [Cd(RaaiR′)4J(CIO4)2 compared to Cd(RaaiR′)I2 or Cd(RaaiR′)2X2 may be associated with the increased mass and rotor volume of the complexes. The rate of isomerization is also dependent on the nature of X and follows the sequence Cd(RaaiR′)2CI2 < Cd(RaaiR′)2Br2 < Cd(RaaiR′)2I2. It may be related to the size and electronegativity of halide, which reduces the effective molar association in the order of I < Br < Cl and hence the rate. Gaussian 03 calculations of representative complexes and free ligands are used to explain the difference in the rates and quantum yields of photoisomerization. [ABSTRACT FROM AUTHOR]

Abstract: Palladium(II) complexes of N-[(2-pyridyl)methyliden]-α(or β)-aminonaphthalene (α or β-NaiPy) are reported in this work. They are spectroscopically characterized along with some mixed ligand complexes, using diimine and azoimine functions. The single crystal X-ray structure of [Pd(N-(2-pyridyl)methyliden-β-aminonaphthalene)Cl2] has been determined. Luminescence properties of the complexes exhibit a ligand centered π–π∗ emission. Quantum yields (ϕ) have been calculated and it has been observed that the complexes of α-NaiPy show higher ϕ values than the complexes of β-NaiPy. Lifetime measurements suggest bi-exponential decay and the average fluorescence lifetime varies from 1.4 to 6.8ns. The spectroscopic properties are correlated with DFT and TD-DFT calculations in two complexes, Pd(β-NaiPy)X2 (X=Cl, I) and they are compared with the free ligand results. [Copyright &y& Elsevier]

Abstract: The reaction of 8-aminoquinoline (8-aq) with M(NO3)2 and M(ClO4)2 (where M=Zn, Cd and Hg) has synthesized complexes of the composition [M(8-aq)2(H2O)2](X)2 (X=NO3, ClO4) whereas MCl2 has isolated M(8-aq)Cl2 type non-ionic compounds. The reaction of M(OAc)2, 8-aq and NaN3/NH4CNS in a 1:1:2mole ratio has separated polynuclear complexes of the composition [M(8-aq)(Y)2]n (Y=N3, NCS). The complexes have been characterized by spectroscopic data and have been structurally confirmed by single crystal X-ray diffraction study in some representative cases. The X-ray structure of [Zn(8-aq)2(H2O)2](NO3)2 shows C–H–π, and π–π interactions and forms a H-bonded sheet (with interactions between the oxygen of NO3 and C(9)–H of 8-aq/coordinated H2O). A novel one-dimensional cadmium(II) azido complex, [Cd(8-aq)(N3)2]n (9), in which the azido takes on an end-on (EO) bridging mode, has been synthesized and characterized. The presence of π–π interactions result in a supramolecular two-dimensional behaviour for the structure. The complexes are photoluminescent at room temperature. [Copyright &y& Elsevier]

Abstract: The reaction of 2-(3′-pyridylazo)imidazole (PyaiH) or 1-alkyl-2-(3′-pyridylazo)imidazole (PyaiR) with in THF or MeCN has synthesized stable red coloured (2a) or (2b–2d). While the reaction of PyaiR and in dry n-heptane has separated shining green compound and has been identified azo-anion radical, [Os(Cl)(CO)(PPh3)2(PyaiR− )] (4b–4d). The reaction performance in n-hexane or toluene is very poor. Upon addition of Cl2 in MeCN to CH2Cl2 solution of 2 or 4 the colour has changed sharply to red-violet and has isolated (3). The reaction of 2 in ethanol with NaBH4 suspension under dinitrogen has reduced coordinated imidazole group to imidazolidine (5). One of the structures of azo-imidazolidinate-hydrido-osmium–carbonyl, [Os(H)(CO)(PPh3)2(PyaiH2)] (5a), is characterized by X-ray diffraction study. Other spectroscopic studies (IR, UV–Vis, NMR) are used to identify the structure of all the complexes. Electrochemistry shows two consecutive anodic peaks (E pa) and suggest irreversible oxidations Os(III)/Os(II), Os(IV)/Os(III) along with azo reductions. [Copyright &y& Elsevier]

Abstract: 1-Alkyl-2-(naphthyl-α/β-azo)imidazole (α-NaiR 1; β-NaiR, 2) react with [Os(H)(Cl)(CO)(PPh3)3] in THF and synthesise [Os(H)(CO)(PPh3)2(α/β-NaiR)](PF6) (3, 4). The X-ray structure of [Os(H)(CO)(PPh3)2(α-NaiEt)](PF6) (3c) shows a distorted octahedral geometry. Other spectroscopic studies (IR, UV–Vis, NMR) support the stereochemistry of the complexes. Addition of Cl2 in MeCN to 3 or 4 gives [Os(Cl)(CO)(α/β-NaiR)(PPh3)2](PF6) (5, 6), which were characterized by spectroscopic studies. The redox properties of the complexes show Os(III)/Os(II), Os(IV)/Os(III) and azo reductions. [Copyright &y& Elsevier]

Abstract: Cadmium(II) complexes of N-[(2-pyridyl)methyliden]-α (or β)-aminonaphthalene (α or β-NaiPy) and 1-alkyl-2-(naphthyl-α (or β)-azo)imidazoles (α- or β-NaiR) using Cl−, and as anions are spectroscopically characterized. Molar conductance data in nitromethane show that the chloro and nitrite compounds are non-conducting, while the perchlorate complexes are 1:2 electrolytes. The single crystal X-ray structure of [Cd(N-{(2-pyridyl)methyliden}-β-aminonaphthalene)2(ONO2)2] has been determined. The luminescence properties of Cd(II) complexes of α/β-NaiPy are studied and they exhibit ligand centered π–π∗ emissions. Naphthylazoimidazoles and their cadmium complexes are non-fluorescent. [Copyright &y& Elsevier]

Neat reaction between Hgl2 and 1-methyl-2-(phenylazo)imidazole (Pai-Me) under microwave irradiation has isolated a novel compound whose structure shows intercalated Hgl2 in the layers of Pai-Me. They exist independently in interpenetrated arrays. In a solution phase study, the same reaction has synthesized an iodo-bridged azoimidazole-Hg(II) complex, [Hg(RaaiR′)(μ-l)(l)]2 (RaaiR′ = 1-alkyl-2-(arylazo)imidazole). The structures have been characterized by X-ray diffraction studies. Chloro-bridged Hg(II) complexes of azoimidazoles, [Hg(RaaiR′)(F-Cl)(Cl)]2, are also known. These complexes upon irradiation with UV light show trans-to-cis isomerization. The reverse transformation, cis-to-trans isomerization, is very slow with visible light irradiation. Quantum yields (øt-c) of trans-to-cis isomerization are calculated, and the free ligand shows higher ø than their Hg(II) complexes. The cis-to-trans isomerization is a thermally induced process. The activation energy (Ea) of cis-to-trans isomerization is calculated by controlled temperature reaction. The Ea's of free ligands are much higher than that of halo-bridged Hg(II)-azoimidazole complexes. Chloro-bridged Hg(II) complexes show lower Ea's than those of iodo-bridged complexes. DFT calculation has been adopted to rationalize the experimental results. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of 1-alkyl-2-(naphthyl-(α/β)-azo)imidazoles [α-NaiR, (1) and β-NaiR (2) where R=Me (a), Et (b), CH2Ph (c)] with Co(OAc)2 ·4H2O and NaN3 in methanol solution has synthesised [Co(α/β-NaiR)2(N3)2] (3, 4). The complexes have been characterized by spectroscopic data and structurally confirmed by single crystal X-ray diffraction data in the case of [Co(β-NaiEt)2(N3)2] (4b). The structure is a severely distorted tetrahedron of CoN4 coordination in which β-NaiEt serves as a monodentate imidazole-N donor ligand. The distortion arises from two weak interactions from Co⋯N(azo) (N(azo) from β-NaiEt). Two weak transitions observed at >600nm are due to the structural distortion. Cyclic voltammetry shows a high potential Co(III)/Co(II) couple along with ligand reductions in the complexes. The tris-chelates, [Co(NaiR)3]2+, are also characterized. [Copyright &y& Elsevier]

Abstract: The reaction of 1-ethyl-2-(phenylazo)imidazole (PaiEt), NaN3 and Mn(OAc)2 ·4H2O at 1:2:1 molar ratio has isolated azido bridge 1-D coordination polymer. In monomeric unit of the complex, MnN6 distorted octahedral coordination is achieved by two EO–N3, two EE–N3 and N,N′-chelation of PaiEt. Bridge angle Mn–(EO)N3–Mn is 98.55(10)°. Variable temperature (300–2K) magnetic measurements determine J values −13.63±0.10 and 2.31±0.15cm−1 and support antiferromagnetic (EE–N3) and ferromagnetic (EO–N3) interaction, respectively. Maximum susceptibility (χ M =0.0251cm3 mol−1) is observed at 43K. [Copyright &y& Elsevier]

Abstract: PbI2 forms iodo-bridged neutral polymer upon reaction with 1-alkyl-2-(arylazo)imidazoles (RaaiR′). The reaction of PbI2 and dialkyl imidazolium iodides [RaaiR′R″]+I− has synthesized {1,3-dialkyl-2-(arylazo)imidazolium} m -{tri-iodoplumbate(II)} m . The complexes are characterized by different spectroscopic studies. Iodobridged chelated polymer, [Pb(RaaiR′)I2] n , has been established by single crystal X-ray diffraction measurements in one case. Tri-iodoplumbates form iodo bridged anion polymer, which connects [RaaiR′R″]+ by hydrogen bonding and are placed in between the pillars of [Pb(μ-I)6] n motif. [Copyright &y& Elsevier]

Abstract: The reaction of 2-(3′-pyridylazo)imidazole (3′-PyaiH) or its 1-alkyl derivative, 3′-PyaiR, with Ru(CO)3(PPh3)2 has synthesized air stable, moisture insensitive, diamagnetic Ru(0) complexes, [Ru(CO)(3′-PyaiR)(PPh3)2]. The ligands serve as an unsymmetric N,N′-chelating agent (N(imidazole) and N(azo) are abbreviated as N and N′, respectively). The X-ray structure determination of [Ru(CO)(3′-PyaiH)(PPh3)2] shows a square pyramidal geometry. The square plane is made up of Ru, 2P, C(O), N(1), and with N(3) at the apex. Other spectroscopic studies (IR, UV–Vis, NMR) support the stereochemistry. Electrochemistry shows three consecutive anodic peaks (E pa) and suggest irreversible redox responses of Ru(I)/Ru(0), Ru(II)/Ru(I), Ru(III)/Ru(II) and azo reductions. Oxidation by Cl2 of [Ru(CO)(3′-PyaiR)(PPh3)2] has isolated the Ru(II)-complex as the perchlorate salt, [Ru(CO)(Cl)(3′-PyaiR)(PPh3)2](ClO4). A solution of RuCl3 and 3′-PyaiR in ethanol has isolated two isomers of the composition Ru(3′-PyaiR)2Cl2. They have been characterized by spectral and electrochemical data. [Copyright &y& Elsevier]

Abstract: Two new series of Zn(II) complexes of α/β-naphthyl-(2-pyridylmethylene)amine and 1-alkyl-2-(naphthyl-α/β-azo)imidazoles with as a counter ion are described in this article. The single crystal X-ray structure of [Zn(β-naphthyl-(2-pyridylmethylene)amine)(N3)2]2 has revealed an end-on azido bridged dimer while [Zn(1-ethyl-2-(naphthyl-β-azo)imidazole)2(N3)2] is a monomer. The complexes are spectroscopically characterized. Examination of luminescence properties of the complexes suggests that the Schiff bases are emissive and the naphthylazo compounds are non-emissive. [Copyright &y& Elsevier]

Abstract: 2-(Arylazo)pyrimidine (p-R-C6H4–NC4H3N2, aapm, R=H (papm, 3a), Me (tapm, 3b), Cl (Clpapm, 3c)) are N,N′-chelating ligands. Platinum(II) complexes, Pt(aapm)Cl2 (4) have been synthesized by the reaction of K2PtCl4 and aapm in MeCN–water under refluxing condition. The reaction of Pt(aapm)Cl2 with ArNH2 in MeCN has synthesized C–N coupled product, Pt(aapm-N–Ar)Cl (5–10). The single crystal X-ray structure determination of one of the compounds has suggested the coupling of ArNH2 at ortho-C–H of the pendant aryl part of aapm in the chelated complex. The stereochemistry and the bonding are described by 1H NMR data. The solution electronic spectra of Pt(aapm-N–Ar)Cl exhibit multiple transition at Vis–NIR region (500–1250nm) which are absent in Pt(aapm)Cl2. Cyclic voltammograms show two quasireversible azo reductions of Pt(aapm)Cl2; Pt(aapm-N–Ar)Cl exhibit four successive redox couples, one of them (positive to SCE) is oxidative in nature and other (negative to SCE) are ligand reductions. [Copyright &y& Elsevier]

Abstract: In the present study, an attempt has been made to explore the neuroprotective and neuroreparative (neurorescue) effect of black tea extract (BTE) in 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson''s disease (PD). In the neuroprotective (BTE + 6-OHDA) and neurorescue (6-OHDA + BTE) experiments, the rats were given 1.5% BTE orally prior to and after intrastriatal 6-OHDA lesion respectively. A significant recovery in d-amphetamine induced circling behavior (stereotypy), spontaneous locomotor activity, dopamine (DA)-D2 receptor binding, striatal DA and 3–4 dihydroxy phenyl acetic acid (DOPAC) level, nigral glutathione level, lipid peroxidation, striatal superoxide dismutase and catalase activity, antiapoptotic and proapoptotic protein level was evident in BTE + 6-OHDA and 6-OHDA + BTE groups, as compared to lesioned animals. BTE treatment, either before or after 6-OHDA administration protected the dopaminergic neurons, as evident by significantly higher number of surviving tyrosine hydroxylase immunoreactive (TH-ir) neurons, increased TH protein level and TH mRNA expression in substantia nigra. However, the degree of improvement in motor and neurochemical deficits was more prominent in rats receiving BTE before 6-OHDA. Results suggest that BTE exerts both neuroprotective and neurorescue effects against 6-OHDA-induced degeneration of the nigrostriatal dopaminergic system, suggesting that possibly daily intake of BTE may slow down the PD progression as well as delay the onset of neurodegenerative processes in PD. [Copyright &y& Elsevier]

Abstract: Heteroleptic tris-chelates, [Ru(bpy)2(α/β-NaiR)](ClO4)2 (bpy=2,2′-bipyridine; α/β-NaiR=1-alkyl-2-(naphthyl-α-azo)imidazole, α-NaiR and 1-alkyl-2-(naphthyl-β-azo)imidazole, β-NaiR) have been synthesized either by reacting Ru(bpy)2Cl2 and α/β-NaiR in presence of 2 equivalent of AgNO3 or from Ru(bpy)2Cl2 +[Ag(α/β-NaiR)2](ClO4) reaction under refluxing condition in MeCN. The single crystal X-ray diffraction study in one case, and by other spectroscopic studies has supported the structure of the complexes. All the complexes show metal-to-ligand charge transfer (MLCT) transitions in the visible region. Cyclic voltammetric studies exhibit high potential Ru(III)/Ru(II) (1.2–1.3V vs. SCE) and three successive ligand reductions at negative to SCE in acetonitrile solution. [Copyright &y& Elsevier]

Abstract: Pyridine and imidazole are connected by an azo group (h name="dbnd" />Nhesize 2-[(3′-pyridyl)azo]imidazole (3′-PyaiH) and this has been confirmed by X-ray structure determination. The N(1)-alkylation gives 1-alkyl-2-[(3′-pyridyl)azo]imidazole (3′-PyaiR′) (R′=Me (2a), Et (2b), Bz (2c)). The reaction between Mn(ClO4)2 ·6H2O and 3′-PyaiR′ in methanol has synthesized [Mn(3′-PyaiR′)4](ClO4)2 (3). The structure has been confirmed by single crystal X-ray diffraction study in one case, in addition to other spectral characterization. The structure reveals a tetrahedral orientation of four ligands coordinating through imidazole-N only. Cyclic voltammetry exhibits a Mn(III)/Mn(II) couple at >1.1V along with azo reductions. However, the reaction of MnCl2 ·4H2O+3′-PyaiR′ in the presence of NaN3 or NH4CNS (1:2:2 mole proportion) has synthesized Mn(3′-PyaiR′)2(X)2 (X=N3 (4), NCS (5)). [Copyright &y& Elsevier]

Abstract: Mercury(II) acetate reacts with the 1-alkyl-2-(arylazo)imidazoles [RaaiR′ where R=H (a), Me (b); R′=Me (1/3/5), Et (2/4/6)] and sodium azide in methanol solution to afford azido bridged polymeric complexes [Hg(RaaiR′)(N3)2]n (3/4). On setting up similar reaction condition, the reaction of Hg(OAc)2 with RaaiR′ and NH4SCN has yielded, instead of polymer, an ion-pair [Hg(RaaiR′)4][Hg(SCN)4] (5/6). The complexes are characterised by elemental analysis, IR, UV–Vis, 1H NMR spectral data and single-crystal X-ray structures of [Hg(HaaiEt)(μ-1,1-N3)2]n (4a) and [Hg(HaaiEt)4][Hg(SCN)4] (6a). The complex 4a is a coordination polymer with end-on (μ-1,1) azido bridge and 6a has tetrahedral structure. [Copyright &y& Elsevier]

Exogenous administration of various neurotrophic factors has been shown to protect neurons in animal model of Parkinson's disease (PD). Several attempts are being made to search a tissue source simultaneously expressing many of these neurotrophic factors. Carotid body (CB) contains oxygen-sensitive glomus cells rich in dopamine (DA) and expresses glial cell line-derived neurotrophic factor, brain-derived neurotrophic factor and neurotrophin-3. We have attempted to study the functional restoration following co-transplantation of CB cells and ventral mesencephalic cells (VMC) in a 6-hydroxydopamine-lesioned rat model of PD. A significant recovery (p < 0.001) in D-amphetamine-induced circling behavior (80%) and spontaneous locomotor activity (85%) was evident in co-transplanted animals at 12 weeks post-transplantation as compared to lesioned animals. Similarly, a significant (p < 0.001) restoration was observed in DA-D2 receptor binding (77%), striatal DA (87%) and 3,4-dihydroxyphenylacetic acid (DOPAC) (85%)levels and nigral DA (75%) and DOPAC (74%) levels. Functional recovery was accompanied by tyrosine hydroxylase (TH) expression and quantification of TH-positive cells by image analysis revealed a significant restoration in TH-immunoreactive (IR) fiber density in striaturn, as well as TH-IR neurons in substantia nigra pars compacta in co-transplanted animals over VMC-transplanted animals. The result suggests that co-transplantation of CB cells along with VMC provides better and long-term functional restoration in the rat model of PD, possibly by supporting the survival of newly grafted cells as well as remaining host DA neurons. [ABSTRACT FROM AUTHOR]

Imidazolyl and 3′-pyridyl are linked by azo bond (–N&z.dbnd6;N–) to synthesize hitherto unknown mixed heterocyclic azo molecules, 2-[(3′-pyridyl)azo]imidazole (3′-PyaiH). Alkylation in presence of NaH has synthesized 1-alkyl-2-[(3′-pyridyl)azo]imidazole (3′-PyaiR′). 3′-PyaiR′ include three types of N-donor centers: N(imidazole), N(azo) and a peripheral N(pyridine). They bind to Ag+ to form 2:2 metallo-macrocycle, [Ag(3′-PyaiR′)]22+, while the reaction with Cd2+ forms Cd(3′-PyaiR′)42+. The complexes are structurally characterized by X-ray diffraction studies. [Copyright &y& Elsevier]

Tris-chelated [Ru(o/p-RaaiR′)3]Cl2 (where RaaiR′=1-alkyl-(2-arylazo)imidazole, R= H (5), p-Me (6) p-OMe (7) o-OMe (8), R′=Me (a), Et (b), CH2Ph (c)) were prepared by the microwave technique. Complexes have been characterized by IR, UV–Vis and 1H NMR spectral data. The structural confirmation has been done in one case, [Ru(o-OMeaaiCH2Ph)3]Cl2. The UV–Vis spectra of the complexes show an intense peak in the visible region (510–570 nm) and it has been assigned to a MLCT transition. Cyclic voltammetry of the complexes shows one metal oxidation Ru(II)/Ru(III) at 1.2–1.5 V and three successive ligand reduction couples negative to SCE as the reference electrode. [Copyright &y& Elsevier]

The reaction of [Ru(OH2)2 (RaaiR')]2+ [RaaiR' = 1-alkyl-2-(arylazo)imidazole, p-R-C6H4-N = N-C3H2-NN(1)-R', R = H (1), Me (2), Cl (3); R' = Me (a), Et (b), CH2Ph (c)] with 8-quinolinol (HQ) in acetone solution followed by the addition of NH4PF6 afforded violet, mixed ligand complexes of composition [Ru(Q)(RaaiR')2](PF6). The structure of [Ru(Q)(MeaaiMe)2](PF6) (2a) has been confirmed by X-ray diffraction studies.Solution electronic spectra exhibit a strong MLCT band at 560-580 nm in MeCN. Cyclic voltammogrames show a Ru(III)/Ru(II)couple at 1.0-1.1 V versus SCE along with three successive ligand reductions. The electronic properties are correlated with EHMO results. [ABSTRACT FROM AUTHOR]

Among trophic factors already known, glial cell line-derived neurotrophic factor (GDNF) and other members of its family have potent and specific action on dopaminergic neurons. In the present investigation an attempt has been made to validate the role of GDNF co-transplantation with fetal ventral mesencephalic cells (VMC) on functional viability and restoration using neurobehavioral, neurochemical and immunohistochemical parameters at 6 weeks post-transplantation in 6-hydroxydopamine (6-OHDA) lesioned rat model of Parkinson’s disease (PD). A significant restoration (P<0.01) in d-amphetamine induced rotations, spontaneous and apomorphine induced locomotor activity in rats co-transplanted with VMC and GDNF was observed as compared to VMC alone transplanted rats. Level of dopamine (DA), 3,4-dihydroxy-phenyl acetic acid (DOPAC) and dopamine D2 (DA-D2) receptors in the caudate putamen (CPu) were significantly (P<0.001) restored in co-transplanted group as compared to VMC transplanted or GDNF administered animals. The functional viability of transplanted VMC was confirmed by tyrosine hydroxylase (TH) expression and quantification of TH-positive cells by image analysis revealed a significant restoration in TH-IR fibers density as well as TH-IR neurons counts in co-transplanted animals over VMC transplanted animals. Results suggest that co-transplantation of VMC and GDNF may be a better approach towards functional restoration in 6-OHDA lesioned rat model of Parkinson’s disease. [Copyright &y& Elsevier]

Cadmium(II) complexes of 1-alkyl-2-(arylazo)imidazoles [RaaiR′ (where R=H (a), Me (b); R′=Me (1/3/5/7), Et (2/4/6/8)] are described in this work. Three representative complexes of the series, [Cd(HaaiMe)2Cl2] (3a), [Cd(HaaiEt)4](ClO4)2 (6a) and [Cd(HaaiMe)4](NO3)2 · 2H2O (7a), have been characterized by single crystal X-ray diffraction measurements. In these complexes, cadmium is seated at the center of a tetrahedron. In [Cd(HaaiMe)2Cl2] (3a), the neutral metallo-organic compound consists of a central cadmium atom surrounded by two HaaiMe ligands and two chlorides. In [Cd(HaaiEt)4] (ClO4)2 (6a), the cation consists of a central cadmium atom surrounded by four HaaiEt ligands. [Cd(HaaiMe)4] (NO3)2 · 2H2O (7a) is a tetragonal channel structure. Nitrate and interstitial water molecules assemble into a square-grid supramolecule (ca. 7 × 7 A˚) and each grid is interlocked by chains parallel to the Z-axis passing through the middle of the square arms to form a layer in the ac- (or bc-) plane with a brick-wall topology (dimension 11.2 × 7 A˚). [Copyright &y& Elsevier]

Dichloro zinc(II) complexes of 1-alkyl-2-(arylazo)imidazole, Zn(RaaiR′)Cl2·H2O (RaaiR′=p-R&z.sbnd;C6H4&z.sbnd;N=N&z.sbnd;C3H2N&z.sbnd;N(1)&z.sbnd;R′: R=H, Me, Cl and R′=Me, CH2CH3, CH2Ph) are characterized by elemental analysis, IR, UV–Vis and 1H NMR spectral data. The reaction of ZnCl2 and RaaiR′ (excess) in the presence of NH4CNS has synthesized Zn(RaaiR′)2(NCS)2. The single-crystal X-ray structure of dichloro-{1-methyl-2-(p-tolylazo)imidazole}zinc(II)-monohydrate (Zn(MeaaiMe)Cl2·H2O) suggests that the complex is distorted trigonal bipyramidal (TBP) around Zn(II) with a trigonal plane constituted from Cl(1), Cl(2), N(imidazole) (N(1)). Molecular packing shows a 1D chain via a hydrogen bonded eight membered ring. The X-ray structure of di-thiocyanato-bis-{1-methyl-2-(phenylazo)-imidazole}zinc(II) also shows a distorted TBP around Zn(II). The coordination sphere is ZnN3 type: where one of the ligands acts as a bidentate chelating agent and the second one coordinates via only the imidazole-N along with two N-centers from the NCS group. [Copyright &y& Elsevier]

The hetero-tris-chelates of the formulae [Ru(phen)(RaaiR′)2](ClO4)2 [phen=1,10-phenanthroline, RaaiR′=1-alkyl-2-(arylazo)imidazole, p-R&z.sbnd;C6H4&z.sbnd;N&z.dbnd6;N&z.sbnd;C3H2&z.sbnd;NN-1-R′, where R=H (a), Me (b), Cl (c) and R′=Me (2), Et (3), CH2Ph (4)] have been isolated from the reaction of ctc-[RuCl2(RaaiR′)2] with AgNO3+phen or [Ag(phen)2](ClO4) in acetone at 40 °C in the dark followed by the addition of NaClO4(aq). The structure of [Ru(phen)(HaaiMe)2](ClO4)2 has been confirmed by X-ray diffraction study and suggested stereoretentive nucleophilic substitution. The structure and stereochemistry of the complexes have been supported by 1H NMR data. Electronic spectra exhibit a strong metal-to-ligand charge transfer (MLCT) band at 515–530 nm along with a weak transition at 700–710 nm. Cyclic voltammograms show a Ru(III)/Ru(II) couple at 1.3–1.4 V versus saturated calomel electrode (SCE) along with three successive ligand reductions. The plot of the difference in potential of the first oxidation and reduction versus energy of the main MLCT band (ν¯CT) is linear. [Copyright &y& Elsevier]

1-Alkyl-2-(naphthyl-(α/β)-azo)imidazoles (α/β-NaiR; R = Me, Et and CH 2 Ph) react with (NH 4 ) 2 [OsCl 6 ] and complexes OsCl 2 (NaiR) 2 are isolated in two isomeric forms: blue-violet ( 3 , 4 ) and red-violet ( 5 , 6 ). The ligand is a bidentate N (N(imidazole)), N′ (N(azo)) donor type. With reference to the pairs of Cl, Cl; N, N and N′, N′ atoms the blue-violet and red-violet isomers are assigned to cis - trans - cis ( ctc ) and cis - cis - cis ( ccc ) configurations respectively. IR spectra of the complexes show two v (Os-Cl) bands and support the cis -OsCl 2 configuration. 1 H NMR spectra also support the ctc and ccc -configuration. The structure of the blue-violet complex OsCl 2 (α-NaiEt) 2 has been determined by X-ray crystallography and the ctc configuration has been confirmed. The structure shows an unusually long N=N bond length, 1.331(4) Å, which is elongated by 0.07 Å compared to the free ligand value. [ABSTRACT FROM AUTHOR]

Reaction in aqueous medium of KReO4 in methanolic solution of RaaiCH2Ph (1-benzyl-2-(arylazo)imidazole) (1) in the presence of perchloric acid has isolated brown products of {[1-benzyl-2-(arylazo)imidazolium][ReO4−]⋅H2O}n, 2. The structural confirmation has been carried out by the single crystal X-ray diffraction study of {[1-benzyl-2-(phenylazo)imidazolium][ReO4−]⋅H2O}, 2a. The molecules are polymerized via hydrogen bonding and form cross-linked network. [Copyright &y& Elsevier]

1-Alkyl-2-(arylazo)imidazoles ( p -R-C 6 H 4 -N=N-C 3 H 2 N 2 X, abbreviated as RaaiX, R = H( a ), CH 3 ( b ), Cl( c ); X = N(1)-CH 3 ( 1 ), N(1)-CH 2 -C 6 H 5 ( 2 )) have been reacted with (NH 4 ) 2 [OsCl 6 ] and OsCl 2 (RaaiX) 2 species isolated in two isomeric forms, blue-violet ( 3 , 5 ) and red-violet ( 4 , 6 ). IR spectra show two ν(Os-Cl) modes and support a cis -OsCl 2 configuration. X-ray diffraction methods were used to determine structures of blue-violet isomers. In terms of the three coordination pairs around Os(II), Cl, Cl, N, N (N(imidazole), N) and N′, N′ (N(azo), N′) the blue-violet isomers have a cis-trans-cis ( ctc ) configuration. 1 H NMR data for the red-violet complexes (isomers B) and results concerning analogous ruthenium(II) complexes indicate isomer B to have cis-cis-cis ( ccc ) configuration. Absorption spectra show an intense MLCT band at ca 580 nm along with two weak bands at 800 and 1000 nm. Cyclic voltammetry shows quasi -reversible Os(III)/Os(II) and Os(IV)/Os(III) couples at 0.4-0.6 V and 1.3-1.5 V versus SCE and ill-defined azo reductions. The X-Ray structures show unusually long N=N bond lengths, 1.31-1.32 Â, elongated by some 0.06 Â compared to the free ligand value. Os(II) prefers to bind N(azo) (Os-N(azo), 1.98 Â) rather than N(imidazole) (Os-N(imidazole), 2.03 Â). EHMO calculations of ctc -OsCl 2 (MeaaiMe) and comparison with the ruthenium(II) complex account for the MLCT transitions in terms of a metal-dominated HOMO to a ligand-dominated LUMO shift. [ABSTRACT FROM AUTHOR]

Reaction of 2-(arylazo)pyrimidines (R&z.sbnd;C6H4&z.sbnd;N&z.dbnd6;N&z.sbnd;C4H3N2, abbreviated aapm; R=H (papm), o-Me (o-tapm), m-Me (m-tapm), p-Me (p-tapm), p-Cl (p-Clpapm)) with (NH4)2[OsCl6] in 2-methoxyethanol gives two isomers of composition OsCl2(aapm)2. They are structurally characterised by 1H NMR spectra and established as the cis–trans–cis (ctc) and cis–cis–cis (ccc) isomer. With reference to the coordination pairs of Cl; N(pyrimidine) (N) and N(azo) (N′), the structure of ctc-OsCl2(p-tapm)2 is confirmed by an X-ray diffraction study. The complexes exhibit multiple MLCT transitions in the visible to near-IR region. Redox studies show an Os(III)/Os(II) couple at 1.2–1.3 V and Os(IV)/Os(III) couple at ∼2 V versus SCE. EHMO calculations and comparison with analogous ruthenium(II) complexes explain the spectral and redox properties of the complexes. [Copyright &y& Elsevier]