N(1)-alkyl-2-(arylazo)imidazoles (RC₆H₄N=NC₃H₂N N(1)X; X=Me (a), Et (b); R=7-Me(L¹), 7-OMe(L²), 7-Cl(L³), 7-NO₂(L⁴) and 8-Me(L⁵)) yield perchlorate salts ofbis-chelated complexes with copper(I). The complexes are 1:1 electrolyte and the composition in supported by Jobs method of continuous variation. The N=N stretching is red shifted by 60–70 cm⁻¹ compared to free ligand values suggesting efficient charge delocalization from Cu(I) to ligand centre. This is supported by high intense MLCT transitions in the visible region. The complexes show highly resolved symmetrical¹H NMR spectra exhibiting C₂-symmetry at least in the NMR time scale. In MeOH the complexes exhibit quasi-reversible CuL₂²⁺/CuL₂⁺ couple at 0.4–0.5 Vvs SCE at 298 K. The high positive potential may be due to the distortion in the geometry of CuL₂⁺.

Arylazoimidazoles (RaaiH,p-R-C₆H₄N=N-C₃H₃N₂, R=H, Me, OMe, Cl and NO₂) are N,N′-chelators. On reaction with (NH₄)₂[OsCl₆], two classes of isomers blue-violetctc-Os(RaaiH)₂Cl₂ and red-violetccc-Os(RaaiH)₂Cl₂ have been isolated. The complexes have been characterised by elemental analyses, IR, UV-Vis and¹H NMR spectral data. The N=N stretching is red shifted by 70–80 cm⁻¹ compared to the free ligand values and indicatesd(Os)→π*(azo) charge shifting. This is supported by MLCT transition in the visible region.¹H NMR spectra suggest that blue-violet isomers areC₂-symmetric and red-violet isomers areC₁-symmetric. Redox studies show the Os(III)/(II) couple of both isomers at 0·6–0·7 Vvs SCE and two successive azo reductions.

2-(Arylazo)pyrimidines (aapm) are N,N′-chelating ligands and synthesise orange-red complexes of composition [Pd(aapm)Cl₂],1, with Pd(MeCN)₂Cl₂ in MeCN. The complex hascis-PdCl₂ configuration [v(Pd-Cl): 340, 360 cm⁻¹]. The treatment of Tollen’s reagent (‘AgOH’) leads to chelatative hydroxylation in the pendant aryl ring, affording a green phenolato complex, Pd(aapmO)Cl,5 (aapmO is deprotonated 2-((8-hydroxo)arylazo)pyrimidine). The reaction is also carried out by controlled addition of dilute sodium hydroxide in air or by the addition of PhIO/m-chloroperbenzoic acid to a MeCN suspension of the complex. A single Pd-Cl stretch at 360 cm⁻¹ supports the composition of phenolato complex. Unlike Pd(aapm)Cl₂ the hydroxylated product, Pd(aapmO)Cl, has a structured intense absorption in the visible region near 670 nm. The Pd-Cl bond in Pd(aapmO)Cl is highly sensitive to nucleophilic substitution and slowly hydrolyses in aqueous medium.

Dechlorination of Ru(PPh₃)₂(TaiMe)Cl₂ (TaiMe = p-Me-C₆H₄-N=N-C₃H₂NN(1)-Me (1), 1-methyl-2-(p-tolylazo)imidazole) has been carried out in acetone solution by Ag⁺ and reacted with N,N’-chelators to synthesise [Ru(PPh₃)₂ (TaiMe)(N,N’)]²⁺. The complexes have been isolated as their perchlorate salts. The N,N’ chelators are 1-alkyl-2-(phenylazo)imidazoles (PaiX, X = Me, Et, CH₂Ph); 2-(arylazo)pyridines, (Raap,p-R-C₆H₄-N=N-C₅H₄N; R = H, Me, Cl); 2-(arylazo)pyrimidines (Raapm,p-R-C₆H₄-N=N-C₃N₂H₂; R = H, Me, Cl); 2,2’-bipyridine (bpy) and 1,10-phenanthroline (o-phen). Unsymmetrical N,N’ chelators may give two isomers and this is indeed observed. The¹H NMR spectral data refer to the presence of two isomers in the mixture in different proportions. With consideration of coordination pairs in the order of PPh₃, PPh₃; N,N (N refers to N(immidazole)) and N’,N (N’ refers to N(azo)), the complexes have been characterised astrans-cis-cis andtrans-trans-trans configuration; the former predominates in the mixture. Electrochemical studies exhibit high potential Ru(III)/Ru(II) couple and quasireversible N=N reduction. Electronic spectra show high intensity (ε ∼ 10⁴) MLCT transition in the visible region (520 ±10) nm along with a shoulder (ε ∼ 10³) in the longer wavelength region.

Two hitherto unknown one-dimensional coordination polymers (1D CPs) [M(adc)(4-spy)₂ (H₂O)₂]_n, (M = Mn(II) (1) and Co(II) (2); H₂adc = acetylenedicarboxylic acid and 4-spy = 4-styrylpyridine) have been characterized by infrared spectra, elemental analysis, thermogravimetric analyses (TGA), powder X-ray diffraction (PXRD) patterns and single-crystal X-ray diffraction techniques. Both these compounds 1 and 2, are isostructural and construct 3D supramolecular networks by the combination of hydrogen bonding and C–H...p interactions. Interestingly, these two materials exhibit variable temperature magnetic moment