Umasankar Ray

Mono- and binuclear cobalt(II)-azido complexes of arylazoimidazole: synthesis, spectral characterization, electrochemistry and crystal structure

Abstract Upon setting up proper reaction conditions 1-alkyl-2-(arylazo)imidazoles (RaaiR′ where R=H (a), Me (b); R′=Me (1/3/5), Et (2/4/6) may react with Co(OAc)2·4H2O and NaN3 in methanolic solution to give two classes of azido complexes: mononuclear bis-chelated [Co(RaaiR′)2(N3)2] (3,4) and binuclear μ-(1,1) azido bridged mono-chelated [Co(RaaiR′)(μ-(1)N3)(μ-(1,1)N3]2 (5,6) complexes. They are characterized by UV–Vis, IR spectra, room temperature magnetism and they have been structurally confirmed by X-ray diffraction study of [Co(MeaaiMe)2(N3)2] (3b) and [Co{(μ-1)N3}(MeaaiMe)]2 (5b). The mononuclear complex (3b) is distorted octahedral whereas the binuclear azide bridged complex (5b) has the distorted square pyramidal geometry around the cobalt(II) centre. Redox properties of the complexes are examined by cyclic voltammetry and show a high potential Co(III)/Co(II) couple along with ligand reductions. EHMO calculation and comparison between the two types of complexes explain the spectral and redox properties of the complexes.

Copper(I)–azoimidazoles: a comparative account on the structure and electronic properties of copper(I) complexes of 1-methyl-2-(phenylazo)imidazole and 1-alkyl-2-(naphthyl-(α/β)-azo)imidazoles

Abstract Bis-[1-alkyl-2-(naphthyl-(α/β)azo)imidazole]copper(I) perchlorate derivatives, [Cu(α-NaiR)2(ClO4)] and Cu(β-NaiR)2](ClO4), have been characterised by spectral and electrochemical studies. The single crystal X-ray structure of bis-[1-ethyl-2-(naphthyl-α-azo)imidazole]copper(I) perchlorate shows strong bonding with two imidazole-N atoms, two azo-N donors interact weakly and the structure is described as having a [2+2] distorted linear geometry. A structural comparison has been done with the X-ray structure of bis-[1-methyl-2-(phenylazo)imidazole]copper(I) perchlorate which is Td symmetric. Solution electronic spectra and redox properties are compared and have been correlated with EHMO calculation.

Studies on the zinc(II)-azoimine system. Single-crystal X-ray structure of Zn(MeaaiMe)Cl2·H2O and Zn(HaaiMe)2(NCS)2 (MeaaiMe=1-methyl-2-(p-tolylazo)imidazole, HaaiMe=1-methyl-2-(phenylazo) imidazole)

Abstract Dichloro zinc(II) complexes of 1-alkyl-2-(arylazo)imidazole, Zn(RaaiR′)Cl2·H2O (RaaiR′=p-RC6H4N=NC3H2NN(1)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.

Synthesis, spectral characterization and X-ray crystal structures of mercury(II)-azoimine compounds

Abstract 1-Ethyl-2-(phenylazo)imidazole (PaiEt, 2) and 2-(arylazo)pyrimidines (Raapm) (RH (3a), p-Me (3b), p-Cl (3c)) are used to synthesize mercury(II) compounds. The complexes are characterized by elemental analysis, IR, UV–Vis, 1H NMR spectral data and single crystal X-ray structures of di[chloro-{1-ethyl-2-(phenylazo)imidazole}(μ-chloro)-mercury(II)] (4) and di[chloro-{2-(phenylazo)pyrimidine} (μ-chloro)-mercury(II)] (5a). The first complex is a centro-symmetric dimer with two highly asymmetric chloro-bridges which make the rhombohedral plane. The second complex forms an unsymmetric trapezohedral geometrical structure.

Silver(I) helicates with 2-(arylazo)pyrimidines. Single crystal X-ray structure of {2-(phenylazo)pyrimidine}silver(I) nitrate

Abstract 2-(Arylazo)pyrimidines (aapm) react with AgNO3 in methanol and crystallises in a single strand right-handed helical coordination polymer, [Ag(aapm)(NO3)]n. The X-ray structure determination of Ag[2-(phenylazo)pyrimidine] (papm) (NO3) (abbreviated, Ag(papm)(NO3)) suggests the triangular coordination around Ag(I) which is made up of chelated azoimine, –NN–CN–, function from one ligand and the third donor centre is coming from meta-related pyrimidine-N of the adjacent papm of the second Ag(papm)-unit. The coordination polymer is propagated through pyrimidine-N→Ag bonding.

Copper coordination compounds of chelating imidazole-azo-aryl ligand. The molecular structures of bis[1-ethyl-2-(p-tolylazo)imidazole]-bis-(azido)copper(II) and bis[1-methyl-2-(phenylazo)imidazole]-bis(thiocyanato)copper(II)

Reaction of Cu(ClO4)2 6H2O with 1-alkyl-2-(arylazo)imidazole [RaaiR′ where R = H (a), Me (b); R′ = Me (1), Et (2)] and NaN3/NH4SCN (1 ∶ 2 ∶ 2 mole ratio) form mononuclear complexes [Cu(RaaiR′)2(N3)2] (3,4) and [Cu(RaaiR′)2(SCN)2]. DMF (5,6). The complexes are characterized by elemental, spectral, electrochemical and other physicochemical results. The structures of both the complexes are confirmed by the single crystal X-ray diffraction studies of [Cu(MeaaiEt)2(N3)2] (4b) and [Cu(HaaiMe)2(SCN)2]. DMF (5a). The complexes are reduced to [Cu(RaaiR′)2]+ by ascorbic acid. However, air oxidation of [Cu(MeaaiEt)2](ClO4) in presence of N3−/SCN− produces [Cu(MeaaiEt)2(N3/NCS)2].

Osmium /azopyrimidine chemistry. Part VII: synthesis, structural characterisation and electrochemistry

Abstract Reaction of 2-(arylazo)pyrimidines (RC6H4NN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.

Hydrogen bonded perrhenate-azoimidazoles

Abstract 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.

1D and 2D network of ReO 4 − bonded azoimidazoles

Abstract 1-Alkyl-2-(arylazo)imidazoles are π-acidic, bidentate chelating molecules. In acid medium imidazole-N centers are protonated and can extract heavy anions. One such example is the binding with ReO4− in acidic medium. 1-Alkyl-2-(arylazo)imidazolium-perrehenate shows hydrogen bonded 1D network. Inclusion of H2O into the molecular frame of 1D increases the dimensionality to 2D network.

Nickel(II)-azido/thiocyanato complexes of 1-alkyl-2-(arylazo) imidazole: single crystal X-ray structure of [Ni(Pai-Me)2(N3)2] (Pai-Me=1-methyl-2(phenylazo)imidazole)

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.