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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: 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: 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]