By proper choice of substituents on the aldehyde and amine, the nature of Schiff base formed (fully condensed or half condensed) could be tuned by the templating effect of the metal ion. Condensation of 5-chlorosalicylaldehyde with ethylene diamine in the presence of Co(II) or Cu(II) and azido anions have afforded two new half condensed Schiff base metal complexes [CuL(µ1,1-N 3)] 2 (1) and [CoL 2 ]N 3 •H 2 O (2), where L = (E)-2-((2-aminoethyl)methyl)-4chlorophenol that were structurally characterized by X-ray analysis, IR and UV spectra. Complex 1 is an asymmetric µ-1,1 azide bridged dimer displaying weak antiferromagnetic interactions (J =-2.93 ± 0.03 cm-1), in agreement with the axial-equatorial N 3-linkage between the two copper centers. Complex 2 is a monomer of low spin Co(III).

The effects of interionic hydrogen bonding and π-π stacking interactions on the physical properties of a new series of picrate anion based ionic liquids (ILs) have been investigated experimentally and theoretically. The existence of aromatic (C2-HO) and aliphatic (C7-HO-N22 and C6-HO-N20) hydrogen bonding and π-π stacking interactions in these ILs has been observed using various spectroscopic techniques. The aromatic and aliphatic C-HO hydrogen bonding interactions are found to have a crucial role in binding the imidazolium cation and picrate anion together. However, the π-π stacking interactions between two successive layers are found to play a decisive role in tight packing in ILs leading to differences in physical properties. The drastic difference in the melting points of the methyl and propyl derivatives (mmimPic and pmimPic respectively) have been found to be primarily due to the difference in the strength and varieties of π-π stacking interactions. While in mmimPic, several different types of π-π stacking interactions between the aromatic rings (such as picrate-picrate, picrate-imidazole and imidazolium-imidazolium cation rings) are observed, only one type of π-π stacking interaction (picrate-picrate rings) is found to exist in the pmimPic IL. NMR spectroscopic studies reveal that the interaction of these ILs with solvent molecules is different and depends on the dielectric constant of the solvent. While an ion solvation model explains the solvation in high dielectric solvents, an ion-pair solvation model is found to be more appropriate for low dielectric constant solvents. The enhanced stability of these investigated picrate ILs compared with that of inorganic picrate salts under high doses of γ radiation clearly indicates the importance of weak interionic interactions in ILs, and also opens up the possibility of the application of picrate ILs as prospective diluents in nuclear separation for advanced fuel cycling process.

Tetradentate Schiff base ligands with multiple coordinaton sites are one of the best choice for the construction of multinuclear metal complexes. Coupled with auxiliary ligands under self assembling conditions, the scope for generating new structures increases manifold due to various structure directing factors in operation. Though, phenoxo or azido bridged copper(II) systems have been investigated thoroughly from structural and magnetic aspects, the literature is scanty with combined phenoxo and azido bridged systems. In a study on the effect of synthetic conditions on the structures generated and associated magnetic properties, two new tetranuclear copper complexes, viz., [Cu4(L1)2(μ‐N3)2(N3)2] (1) and [Cu4(L2)2(μ‐N3)2(N3)2] (2) where L1=N,N′‐Bis(salicylidene)diaminopropane (salpn) and L2=N,N′‐Bis(salicylidene)diaminobenzene (salophen) with both phenoxo and azido bridges are reported. The tetranuclear cluster is made of two inversion related dimers built of phenoxo bridged Cu1 and Cu2 with distorted square planar and square pyramidal geometries respectively. These dimers are bridged by symmetrically bridging azides leading to a tetranuclear core. The contrasting magnetic behavior inspite of same coordination environments, antiferromagnetic in 1 (J1=−2.17 cm−1; J2=−28.15 cm−1) and ferromagnetic in 2 (J1=−74.7 cm−1; J2=146.5 cm−1), is understood in terms of lower bridge angles and closer separation between copper centers in 2 than in 1.

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