Complexation reactions of bivalent metal ions and ethyl-2,3-dioxobutyrate-2p-bromophenylhydrazone (EDOB-2p-BPH) have been studied potentiometrically in 50% (v/v) ethanol/water medium at different ionic strengths with respect to NaClO₄ and at different temperatures and their stability constants determined. The method of Bjerrum and Calvin as modified by Irving and Rossotti has been used to determine then andpL values. S_min values which have the same significance as ‘T²’ have also been calculated. The thermodynamic stability constants and standard free energy change (ΔG) have also been calculated. ΔG values are negative in all cases indicating that the reactions are spontaneous. The ligand field stabilization energy (δH) has also been calculated for the 3d transition metals.

The U V-VIS spectra of molecular complexes of paraquat with ring and N-substituted anilines have been recorded in methanol and 50% v/v aqueous methanol. All the complexes exhibited well-resolved charge transfer bands in the wavelength region where neither of the components have any absorption. The energies of charge transfer bands of the substituted aniline-paraquat complexes bear linear relationships with the ionization potentials obtained from the substituted aniline-TCNE complexes, indicating π - π interaction between paraquat and the donors. Both ring and N-substituents have effects on the positions of the CT bands as well as on the stabilities of the complexes. The positions of the CT bands are shifted to shorter wavelengths and the stabilities of the complexes decrease on going from methanol to aqueous. methanol.

A new series of layered oxides, Li₃(Li_1.5xFe_3−(x+1.5x)Te_x)O₆, (0.1 ≤ 𝑥 ≤ 1.0) possessing rock-salt superstructures crystallizing in monoclinic (S.G. C2/m) symmetry is reported here. Investigations based on single crystal and powder X-ray diffraction studies for the 𝑥 = 1 member, Li₃(Li_1.5Fe_0.5Te)O₆, (a=5.1834(1); b=8.8858(2); c=5.16840(8) Å; 𝛽=110.660(1)°) confirmed the stabilization of (Li_1.5Fe_0.5Te_1.0O₆)³⁻ honeycomb arrays with a very high amount of lithium ions. The structure for the x = 0.5 member (Li_3.75Fe_1.75Te_0.5O₆) has also been confirmed by the powder X-ray diffraction Rietveld refinements. Li₃(Li_1.5Fe_0.5Te)O₆ and Li₃(Li_0.75Fe_1.75Te_0.5)O₆ oxides exhibited Curie–Weiss behaviour in the temperature range of 50–300 K with negative 𝜃 values. Their respective ionic conductivities were found to be 6.76 × 10⁻⁵ S cm⁻¹ and 2.21 × 10⁻⁶ S cm⁻¹ at 573 K. The UV-visible diffuse reflectance measurements for the differentmembers of the series Li₃(Li_1.5xFe_3−(x+1.5x)Te_x)O₆, (0.1 ≤ 𝑥 ≤ 1.0) show the expected shifts in their absorptionedges based on the increasing amount of Fe³⁺ions starting from 𝑥 = 1.0 member to 𝑥 = 0.1 member

In this perspective article, the basic theory and applications of the “Quantum Theory of Atoms in Molecules” have been presented with examples from different categories of weak and hydrogen bonded molecular systems.