Search

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: 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: 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]

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]

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]