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.

A dysprosium-based metallo-organic framework (MOF) containing calcium ions formulated as {Dy(pyda)₃Ca_1.5(H₂O)₆} · 5.5H₂O (1) (H₂pyda = pyridine-2,6-dicarboxylic acid) was solvothermally synthesized in ethanolic medium and characterized by physico-chemical and spectroscopic tools. A detailed structural analysis of the solid state structure of 1 by single crystal X-ray diffraction study showed a tricapped trigonal prism geometry for lanthanide in the [Dy(pyda)3]3− fragment. The mode of interaction of 1 with calf thymus- DNA and with protein bovine serum albumin (BSA) was investigated by using absorption and emission spectroscopic tools. The apparent association constant of complex 1 with CT-DNA was deduced from an absorption spectral study ($K_b = 4.08 \times 10^4$ M^-1). Spectral and viscosity measurements indicated a groove-binding mode of 1 with CT-DNA, and from spectroscopic study the formation of a metal complex-BSA adduct was assumed to be the result of the interaction of 1 with BSA.

Two mononuclear zinc(II) complexes of newly designed carboxamide derivatives, formulated as [Zn(L¹)₃](ClO₄)₂ (1) and [Zn(L²)₃](ClO₄)₂ (2) [where L¹ = 𝑁-(furan-2-ylmethyl)-2-pyridinecarboxamide and L² = 𝑁-(thiophen-2-ylmethyl)-2-pyridine-carboxamide], have been isolated in pure form in the reaction of perchlorate salts of Zn(II) with ligands L¹ and L², respectively. The two complexes were characterized by physicochemical and spectroscopic tools, and by X-ray crystal structures of both ligands and the complex 1. In complex 1, zinc(II) is chelated by three ligands with a distorted octahedral geometry. The DNA-binding properties of zinc complexes 1 and 2 have been investigated by spectroscopic methods and viscosity measurements. The results suggest that both complexes 1 and 2 bind to DNA in an intercalation mode between the uncoordinated furan or thiophene chromophore and the base pairs of DNA.

A series of neutral hexacoordinated nickel(II) complexes of formula [Ni^II (L)X₂] (where L = 3,4-bis(2-pyridylmethylthio)toluene with tetradentate N₂S₂ donor set and X = chloride (1), azide (2), cyanate (3) and isothiocyanate anion (4)) have been synthesized and isolated in pure form. The complexes were characterized by physicochemical and spectroscopic methods along with detailed structural characterization of 1,2 and 3 by single crystal X-ray diffraction analyses. The structural study showed that the nickel(II) ion has a distorted octahedral geometry being chelated by the tetradentate N₂S₂ ligand and bound to cis- located choride or pseudohalide anions. In dimethylformamide solution the complexes showed quasi-reversible Ni^II/Ni^III redox couples in cyclic voltammograms with E_1/2 values of +0.723, +0.749, +0.768 and +0.868 V for 1, 2, 3 and 4, respectively. The study of interaction of the complexes with calf thymus DNA, bovine serum albumin (BSA) and human serum albumin (HSA) using spectroscopic and physicochemical tools clearly indicates that the complexes interact with DNA via groove binding mode.

Treatment of perchlorate or nitrate salt of cadmium(II) with carboxamide derivatives (L) generated four novel mononuclear metal complexes, represented as [Cd(L)₄](ClO₄)₂ (1a and 1b) and [Cd(L)₂(ONO₂)₂] (2a and 2b) in appreciable yields (L = L¹ = N-(furan-2-ylmethyl)-2-pyridine carboxamide and L = L² = N-(thiophen-2-ylmethyl)-2-pyridine carboxamide). The complexes have been characterized by FT-IR, UVVisible, elemental analysis and single crystal X-ray crystallographic analysis which revealed eight coordinated cadmium ions, but in different coordination environments, depending on the counter anion used. In addition,electronic absorption, fluorescence spectroscopy and viscosity measurements revealed a significant interaction of the four complexes with CT-DNA via intercalative/groove binding mode. The intrinsic binding constant K_bobtained varies from 0.4 × 10⁴ to 1.11 × 10⁵ M⁻¹. The results suggest that neutral complexes 2a and 2b bind to DNA in an intercalative mode. On the other hand, cationic complexes 1a and 1b bind with DNA via weak electrostatic/covalent interaction.

Anewrhodamine-based Schiff base (L) has been synthesized and characterized by physicochemical and spectroscopic tools. This organic molecule selectively reacts with Cu²⁺ ions with a remarkably significant optical change, which supports the development of a chemosensor for Cu²⁺ ions as low as nanomolar level in aqueous medium. On the basis of the experimental work, the ‘turn-on’ colorimetric/fluorimetric spectroscopic change is due to Cu²⁺ ion-assisted hydrolysis followed by spirolactam ring opening of the probe (L) in 20mM HEPES buffer [pH 7.4; water/acetonitrile (9:1 v/v)]. The competitive ions do not affect the selectivity and specificity of the probe (L) in the detection of Cu²⁺ ions. The cell imaging study using fluorescence microscope showed that this non-cytotoxic probe is useful to detect the distribution of Cu²⁺ ions in AGS cells lines.