Ruthenium azo complexes: Synthesis,spectra, and electrochemistry of dithiocyanato-bis{1-(alkyl)-2-(arylazo)imidazole}ruthenium(II)

Silver-assisted aquation of blue cis-trans-cis-RuCl₂(RAaiR’)₂ (I) leads to the synthesis of solvento species, blue-violet cis-trans-cis-[Ru(OH₂)₂(RAaiR’)₂](ClO₄)₂ (II), where RAaiR’ = p-R-C₆H₄-N=N-C₃H₂-NN, abbreviated as N,N′ chelator (N(imidazole) and N(azo) represent N and N′, respectively); R = H (a), p-Me (b), p-Cl(c); R′ = Me (III), Et (IV), Bz (V), that reacted with NCS⁻ in warm EtOH resulting in red-violet dithiocyanato complexes of the type [Ru(NCS)₂(RAaiR)₂] (IIIa–Vn). These complexes were studied by elemental analysis, UV-Vis, IR, and ¹H NMR spectroscopy and cyclic voltammetry. The solution structure and stereoretentive transformation in each step have been established from ¹H NMR results. All the complexes exhibit strong MLCT transitions in the visible region. They are redox active and display one metal-centered oxidation and successive ligand-based reductions. Linkage isomerisation was studied by changing the solvent and then by UV-Vis spectral analysis.     

Synthesis, spectral characterization and redox properties of iron (II) complexes of 1-alkyl-2-(arylazo)imidazole

Iron (II) complexes of 1-alkyl-2-(arylazo)imidazoles (p-R-C₆H₄-N=N-C₃H₂NN-1-R′, R = H (a), Me (b), Cl (c) and R′ = Me (1/3), Et (2/4) have been synthesized and formulated astris-chelates Fe(RaaiR′) ₃ ²⁺ . They are characterized by microanalytical, conductance, UV-Vis, IR, magnetic (polycrystalline state) data. The complexes are low spin in character,t _2g ⁶ (Fe(II)) configurations.     

Synthesis,spectral characterisation and electrochemical studies of dichloro-{1-benzyl-2-(arylazo)imidazole}platinum(II) complexes and their dioxolene derivatives

1-Benzyl-2-(arylazo)imidazoles, p-RC₆H₄N=NC₃H₂-N₂1-CH₂Ph [RaaiBz (2); R=H(a), Me(b), Cl(c)], react with K₂PtCl₄ in boiling MeCN–H₂O (1:1 v/v) to give brownish-red Pt(RaaiBz)Cl₂ (3) complexes. Addition of dioxolene in the presence of Et₃N to a CHCl₃–MeOH solution of Pt(RaaiBz)Cl₂ yields green mixed complexes of composition [Pt(RaaiBz)(O,O)] [O,O = catecholate (cat) (4); 4-tert-butylcatecholate (tbcat), (5); 3,5-di-tert-butylcatecholate (dtbcat), (6); tetracholorocatecholate (tccat), (7)] which were characterised by elemental analyses, i.r., u.v.–vis.–near i.r. and ¹H-n.m.r. spectral data. The solution electronic spectra exhibit ligand-to-ligand charge-transfer (l.l.c.t) transitions in the red to near i.r. region; the position and symmetry of the band depend upon the substituent on the dioxolene and arylazoimidazole. This effect is qualitatively assigned as HOMO(dioxolene) LUMO(RaaiBz). A cyclic voltammogram of the dioxolene complex reveals two consecutive oxidative couples corresponding to catechols to semiquinones and semiquinone to quinone, respectively and the reductive couples represent azo reductions.     

Kinetics and Mechanism of the Reactions of Picolinic Acid with Dichloro-{1-alkyl-2-(arylazo)imidazole}palladium(II) Complexes

The reaction between Pd(N,N′)Cl₂ [N,N′ ≡ 1-alkyl-2-(arylazo)imidazole (N,N′) and picolinic acid (picH) have been studied spectrophotometrically at λ = 463 nm in MeCN at 298 K. The product is [Pd(pic)₂] which has been verified by the synthesis of the pure compound from Na₂[PdCl₄] and picH. The kinetics of the nucleophilic substitution reaction have been studied under pseudo-first-order conditions. The reaction proceeds in a two-step-consecutive manner (A → B → C); each step follows first order kinetics with respect to each complex and picH where the rate equations are: Rate 1 = {k′₀ + k′₂[picH]₀} × [Pd(N,N′)Cl₂] and Rate 2 = {k′′₀ + k′′₂[picH]₀}[Pd(N,O)(monodentate N,N′)Cl₂] such that the first step second order rate constant (k′₂) is greater than the second step second order rate constant (k′′₂). External addition of Cl⁻ (as LiCl) suppresses the rate. Increase in π-acidity of the N,N′ ligand, increases the rate. The reaction has been studied at different temperatures and the activation parameters (Δ^‡H° and Δ^‡S°) were calculated from the Eyring plot.     

Reaction of Ru(PPh3)3Cl2 with arylazoimidazoles: spectral characterisation and redox studies of [bis-{N(1)-alkyl-2-(arylazo)imidazole}-bis-(triphenylphosphine)]-ruthenium(II) perchlorate

Ru(PPh₃)₃Cl₂ reacts with N(1)-alkyl-2-(arylazo)imidazoles, p-RC₆H₄N=NC₃H₂N₂X, [RaaiX, R = H(a), Me(b), Cl(c); X = Me(1), Et(2), Bz(3)] under refluxing conditions in EtOH to give [Ru(RaaiX)₂(PPh₃)₂](ClO₄)₂ · H₂O complexes (4–6). RaaiX is a bidentate chelator (N, N) with N(imidazole), N and N(azo), N donor centres. Three isomers are present in the mixture in which the pairs of PPh₃, N and N occupy cis–cis–trans, cis–trans–cis and cis–cis–cis, positions respectively. The isomers were identified by ¹H-n.m.r. spectra. Four signals are observed in the aliphatic zone for N(1)-X; two are of equal intensity at higher and the other two signals at lower in the ratio 1:0.3:0.2 suggesting the presence of cis–cis–cis, cis–trans–cis and cis–cis–trans-geometry. The complexes display the allowed t ₂(Ru) ^*(RaaiX) transition. Cyclic voltammetry indicates two consecutive Ru^III/II couples along with azo reductions.     

Synthesis, spectral and electrochemical behaviour of cytosinato bridged complexes of ruthenium(II) and platinum(II) with 1-alkyl-2-(arylazo)imidazoles

Dechlorination of M(RaaiR′) _n Cl₂ by AgNO₃ produced [M(RaaiR′) _n (MeCN)₂]⁺² [M = Ru(II), n = 2; Pt(II), n = 1; RaaiR′ = 1-alkyl-2-(arylazo)imidazole)] which upon reaction with the nucleobase cytosine (C) in MeCN solution gave cytosinato bridged dimeric compounds which were isolated as perchlorate salts [M₂(RaaiR′) _n (C)₂](ClO₄)₂ · H₂O. The products were characterized by IR, u.v.–vis., ¹H-n.m.r. spectroscopy and cyclic voltammetry. In MeCN solution the ruthenium complexes exhibit a strong MLCT band at 550–555 nm and two redox couples positive to SCE due to two metal-center oxidation along with ligand reduction, negative to SCE. The platinum complexes show a weak transition at 500–520 nm in MeCN and exhibit only ligand reduction in cyclic voltammetry. The coordination of the ligand was supported by ¹H-n.m.r. spectral data.     

Synthesis,Spectra and Electrochemistry of Dinitro-bis-{1-alkyl-2-(arylazo) imidazole} Ruthenium(II). Nitro-nitroso Derivatives and Reactivity of the Electrophilic {Ru-NO}<Superscript>6</Superscript>System

Ag⁺ assisted aquation of blue cis-trans-cis-RuCl₂(RaaiR′)₂ (4–6) leads to the synthesis of solvento species, blue-violet cis-trans-cis-[Ru(OH₂)₂(RaaiR′)₂](ClO₄)₂ [Raai R′=p-R-C₆H₄ N=N–C₃H₂–NN–1–R′, (1–3), abbreviated as N,N′-chelator, where N(imidazole) and N(azo) represent N and N′, respectively; R = H (a), OMe (b), NO₂ (c) and R′ = Me (1/4/7/10), CH₂CH₃ (2/5/8/11), CH₂Ph (3/6/9/12)] that have been reacted with NO₂⁻in warm EtOH resulting in violet dinitro complexes of the type, Ru(NO₂)₂(RaaiR′)₂ (7–9). The nitrite complexes are useful synthons of electrophilic nitrosyls, and on triturating the compounds, (7b–9b) with conc. HClO₄ nitro-nitrosyl derivatives, [Ru(NO₂)(NO)(OMeaaiR′)₂](ClO₄)₂ (10b–12b) are isolated. The solution structure and stereoretentive transformation in each step have been established from ¹H n.m.r. results. All the complexes exhibit strong MLCT transitions in the visible region. They are redox active and display one metal-centred oxidation and successive ligand-based reductions. The redox potentials of Ru(III)/Ru(II) (E_1/2^M) of (10b–12b) are anodically shifted by ∼ ∼0.2 V as compared to those of dinitro precursors, (7b–9b). The ν(NO) >1900 cm⁻¹ strongly suggests the presence of linear Ru–NO bonding. The electrophilic behaviour of metal bound nitrosyl has been proved in one case (12b) by reacting with a bicyclic ketone, camphor, containing an active methylene group and an arylhydrazone with an active methine group, and the heteroleptic tris chelates thus formed have been characterised.     

Use of steric crowding to synthesise ruthenium(II) N(1)-alkyl-2-(arylazo)imidazole isomers. Spectral characterization and redox studies

Complexes of N(1)-methyl- and N(1)-benzyl-2-(dimethylphenylazo)imidazoles with ruthenium(II) have been prepared and characterised by physico-chemical and spectroscopic means. The 7,8-dimethylphenylazo ligands gave four stereoisomers, whereas the 8,9-dimethylphenylazo ligands gave only two. Isomer assignments are made on the basis of i.r. and ¹H-n.m.r. data. Redox studies show the Ru^III/II couple at 0.4–0.5 V (versus s.c.e) for the trans,cis,cis-isomers, whereas the other isomers exhibit higher (0.6–0.7 V) potentials. Two successive azo reductions are observed at negative potentials. The difference between the first metal and ligand redox potentials is linearly correlated with CT [t₂(Ru) ^*(RL)].     

Ruthenium-azoimine-chloranilates Synthesis,Spectra and Electrochemistry of Ruthenium(II)-1-alkyl-2-(arylazo)imidazole-chloranilate Complexes

Ag⁺-assisted dechlorination of blue cis-trans-cis Ru(R-aai-R′)₂Cl₂ followed by the reaction with chloranilic acid (H₂CA) in the presence of Et₃N, gives a neutral mononuclear violet complex [Ru(R-aai-R′)₂(CA)]. [R-aai-R′=p-R-C₆H₄—N=N—C₃H₂—NN, abbreviated as an N,N′ chelator where N(imidazole) and N(azo) represent N and N′, respectively; R = H (a), OMe (b), NO₂ (c) and R′= Me (4), Et(5), Bz(6)]. All the complexes exhibit strong intense MLCT transitions in the visible region and weak broad bands at higher wavelength (>700 nm). Visible transitions (580–595 nm) show a negative solvatochromic effect. The cyclic voltammograms show two quasireversible to irreversible couples positive to SCE and are due to CA⁻/CA²⁻ (1.2–1.35 V) and Ru(III)/Ru(II) (1.6–1.8 V) redox processes. Three couples, negative to SCE, are assigned to CA²⁻/CA³⁻ (−0.2 to −0.3 V), and azo reductions (−0.5 to −0.7, −0.8 to −0.9 V) of the chelated R-aai-R′.     

Kinetics and mechanism of nucleophilic substitution of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II) by pyridine bases

The reaction of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II), Pd(RaaiMe)Cl₂ where RaaiMe = p-R–C₆H₄N=N–C₃H₂N₂-1-Me; R = H(1), Me(2), Cl(3), with pyridine bases [RPY: R = H (a), 4-Me (b), 4-Cl (c), 2-Me (d), 2,6-Me₂ (e), 2,4,6-Me₃ (f)] has been studied spectrophotometrically in MeCN at 451 nm. The products (4) have been isolated and characterised as trans-Pd(RPy)₂Cl₂. The kinetics of the nucleophilic substitution has been examined under pseudo-first-order conditions at 298 K. A single phase reaction step has been observed for bases such as Hpy (a), 4-MePy (b) and 4-ClPy (c) and follows the rate law: rate = (a + k[RPy]²[Pd(RaaiMe)Cl₂]). The bases 2-MePy (d), 2,6-Me₂Py (e) and 2,4,6-Me₃Py (f) exhibits a bi-phasic reaction and follows the rate laws: rate–1 = (a + k[RPy][Pd(RaaiMe)Cl₂]) and rate–2 = (a + k[RPy][Pd(RaaiMe)-Cl₂]), where k is the third-order rate constant; k is the second-order first phase rate constant, k is the second-order second phase rate constant and a/a/a correspond to the solvent dependent constant of the respective reaction path. The rate data supports a nucleophilic association path. External addition of Cl^– (LiCl) suppresses the rate, which follows the order: k/k/k (3) > k/k,k (1) > k/k,k (2). The k values are linearly related to the Hammett constants. The 2-substituted pyridines (d–f) remarkably reduce the rate and show a bi-phasic reaction behaviour as compared with 4-Rpy (a–c). This is attributed to the steric effect that destabilises the transition state. The rate decreases with increasing steric crowding at the ortho-position and follows the order: (d) > (f) > (e). The 4-substituted pyridines control the rate via an inductive effect and follow the order: (b) > (a) > (c).     

Reactions of dichloro-bis-[N(1)-benzyl-2-(arylazo)imidazole] ruthenium(II) with tertiary phosphines

The title reaction proceeds smoothly in MeOH-H2O togive the salts [RuCl(P)L2](ClO4), H2O (1, 2) or [Ru(PP)L2](ClO4)2, H2O (3, 4) where L=N(1)-benzyl-2-(arylazo)imidazole, P=PPh3, or PPh2Me, and PP=Ph2P(CH2)2PPh2 (dppe) or Ph2P(CH2)3PPh2(dppp). The complexes have been characterised by physico-chemical and spectroscopic methods.     

Reaction of trans-dichloro-bis[N(1)-methyl-2-(arylazo)imidazole] ruthenium(II) with tertiary phosphines

Trans-dichloro-bis[N(1)-methyl-2-(arylazo)imidazol e] ruthenium(II) (tcc-Ru(MeL)2Cl2) reacts with tertiary phosphines giving rise to species of type [RuCl(P)-(MeL)2]+ and [Ru(P-P)(MeL)2]2+ in which Cl, P and P-P respectively occupy cis-positions [P=PPh3, or PPh2Me; P-P=Ph2P(CH2)2PPh2 (dppe) or Ph2P (CH2)3PPh2 (dppp)]. The cations have been isolated as perchlorates. The complexes display allowed t2(Ru) *(MeL) transitions in the visible region and show the energy ordering [RuCl(P)(MeL)2]+<[Ru(P-P) (MeL)2]2+. The RuIII/II couple occurs at high potentials, >1.1 V versus s.c.e. The azo reduction is sensitive to the nature of substituents in the ligand. The 1H n.m.r. spectra of the complexes are compatible with the isomer of C1-symmetry.     

Kinetics and mechanistic studies of the interaction of thiosulfate with cis-diaqua-bis[1-alkyl-2-(arylazo)imidazole]ruthenium(II) complexes

The nucleophilic substitution reaction of S₂O₃²⁻ with [Ru(HaaiR′)₂(OH₂)₂](ClO₄)₂ (1) [HaaiR′ = 1-alkyl-2-(phenylazo)imidazole] and [Ru(ClaaiR′)₂(OH₂)₂](ClO₄)₂ (2) [ClaaiR′ = 1-alkyl-2-(chlorophenylazo)imidazole] [where R′ = Me(a), Et(b) or Bz(c)] in acetonitrile–water (50% v/v) medium to yield Na₂[Ru(HaaiR′)₂(S₂O₃)₂] (3a, 3b or 3c) and Na₂[Ru(ClaaiR′)₂(S₂O₃)₂] (4a, 4b or 4c) has been studied. The products were characterized by microanalytical data and spectroscopic techniques (UV–Vis, NMR and mass spectroscopy). The reaction proceeds in two consecutive steps (A → B → C); each step follows first order kinetics with respect to each complex and S₂O₃²⁻, and the first step second order rate constant (k′₂) is greater than the second step one (k″₂). An increase in the π-acidity of the ligand increases the rate. Thermodynamic parameters, the standard enthalpy of activation (Δ^‡H⁰) and the standard entropy of activation (Δ^‡S⁰), have been calculated for both steps using the Eyring equation from variable temperature kinetic studies. The low Δ^‡H⁰ and large negative Δ^‡S⁰ values indicate an associative mode of activation for both aqua ligand substitution processes.     

Synthesis,spectral and electrochemical studies of isomeric dichloro-bis[N(1)-ethyl-2-(arylazo)imidazole]ruthenium(II) and the reaction of the green isomer with tertiary phosphines

N(1)-Ethyl-2-(arylazo)imidazoles (L) react with RuCl₃ giving green (5) and blue RuL₂Cl₂ (6) isomers. The green isomer is quantitatively transformed into the blue isomer on boiling under reflux in 1,2-dichlorobenzene. The ligand is of the N,N-chelating type and in principle, provides five geometrical isomers. Considering the coordination pairs in the order: Cl, N(imidazole), N and N(azo),N the green isomer isspectroscopically characterised as trans-cis-cis-tcc-RuL₂Cl₂ (5) and the blue isomer is cis-trans-cis-ctc-RuL₂Cl₂ (6). The green isomer reacts smoothly with tertiary phosphines giving species of type [RuCl(P)L₂]⁺ (7,8) and [Ru(P-P)L₂]⁺² (9,10) in which Cl, P and P-P respectively occupy cis-positions [P = PPh₃, PPh₂Me, P-P = Ph₂P(CH₂)₂PPh₂ (dppe) and Ph₂P(CH₂)₃PPh₂ (dppp)]. All the complexes display allowed t₂(Ru) ^* (L) transitions in the visible region. A systematic shift of this MLCT band to higher energy occurs in the order: tcc-RuL₂Cl₂ (5) < ctc-RuL₂Cl₂ (6) < [RuCl(P)L₂]⁺ (7,8) < [Ru- (PP)L₂]⁺² (9,10). The Ru^III/Ru^II couple (E⁰ _M) occurs 0.6–0.8V in green tcc-RuL₂Cl₂ (5), 0.7–0.9V in blue ctc-RuL₂Cl₂ (6) and the high potentials observed (> 1.2V versus s.c.e.) in phosphine derivatives (7–10). The azo reduction (E⁰ _L) appears at negative values with respect to s.c.e. and is found to be sensitive to substitution in the phenyl ring of the ligand frame. The potential difference (E⁰ _M–E⁰ _L) is linearly related to the MLCT band energies (_CT) of green and blue RuL₂Cl₂ complexes. The phosphine derivatives behave differently, a linear correlation being observed between _CT and E⁰ _M. The isomer configuration of RuL₂Cl₂ and the stereochemistries of the phosphine derivatives are established by ¹H n.m.r. spectral data. The green (5) and blue (6) isomers exhibit single -Me or -OMe signals indicatives of C₂-symmetry. The phosphine complexes [Ru(P)Cl(L₂)₂]⁺/[Ru(P-P)(L₂)₂]⁺² show two equally intense methyl signals suggesting C₁-symmetry in the derivatives.     

Copper(I) and Silver(I) Complexes of 1-alkyl-2-(methyl)-4-(arylazo)imidazole. Synthesis, Spectral Studies and Electrochemistry

2-(Methyl)-4-(arylazo)imidazole (RLH) (1, 2) are new series of azoimidazoles. Upon treatment of alkylhalide in dry THF in presence of NaH has synthesised 1-alkyl-2-(methyl)-4-(arylazo)imidazole (RLR′) (3, 4). They belong to the azoimine family of N,N′-chelating ligand. They stabilize the Cu(I) oxidation state and we have synthesized [Cu(RLR′)₂](ClO₄) (5, 6). These complexes show a moderately intense visible band (500–600 nm) which has been assigned to 3d(Cu) → π*(ligand) transition. Ag(I) complexes of RLR′ (7, 8) are also very stable under ambient conditions and show weak transitions in the visible region. The Cu(I)-complexes show high potential Cu(II)/Cu(I) redox couple > 0.4 V vs Ag, AgCl/Cl⁻ reference electrode. All these complexes have been structurally characterized by ¹H NMR spectroscopic data.     

Kinetic and mechanistic studies of the interaction of 2-mercapto pyridine with dichloro[1-alkyl-2-(arylazo)imidazole]palladium(II) complexes

Nucleophilic substitution of Pd(RaaiR′)Cl₂ [(RaaiR′ = 1-alkyl-2-(arylazo)imidazole, p-R-C₆H₄-N=N-C₃H₂NN-1-R′; where R = H(a)/ Me(b)/ Cl(c) and R′ = Et(1)/Bz(2)] with 2-Mercaptopyridine (2-SH-Py) in acetonitrile (MeCN) at 298 K, to form [Pd₂(2-S-Py)₄], has been studied spectrophotometrically under pseudo-first-order conditions and the analyses support the nucleophilic association path. The reaction follows the rate law, Rate = {k ₀ + k [2-SH-Py] ₀ ² }[Pd(RaaiR′)Cl₂]: first order in Pd(RaaiR′)Cl₂ and second order in 2-SH-Py. The rate of the reaction follows the order: Pd(RaaiEt)Cl₂ (1) < Pd(RaaiBz)Cl₂ (2) and Pd(MeaaiR′)Cl₂ (b) < Pd(HaaiR′)Cl₂ (a) < Pd(ClaaiR′)Cl₂ (c). External addition of Cl⁻ (LiCl) and HCl suppresses the rate (Rate ∝ 1/[Cl⁻]₀ & ∝1/[HCl]₀). The reactions have been studied at different temperatures (293–308 K) and activation parameters (Δ^‡ H° and Δ ^‡ S°) of the reactions were calculated from the Eyring plot and support the proposed mechanism.     

Nickel(II)-azido/thiocyanato complexes of 1-alkyl-2-(naphthylazo)imidazole

[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 0.3–0.4 V which is corresponding to Ni(III)/Ni(II) couple along with ligand reductions at negative potential to SCE reference electrode.     

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.     

Chemistry of azoimidazoles. Synthesis,spectral characterization and redox studies of N(1)-benzyl-2-(arylazo)imidazolepalladium(II)chloride

Arylazoimidazoles (2) are N,N-chelating ligands. The polymerization trend of the azolate system is restricted via N(1)-benzylation. The parent molecules (2), N(1)-benzylated products (3) and palladium complexes (4) were made by standard methods. The ligands (3) and complexes (4) are new. They have been characterized by elemental analysis, i.r., u.v.-vis. and high resolution 1H-n.m.r. spectral data. Redox studies were carried out by cyclic voltammetry. On complexation, azo reduction is shifted anodically.