Slow magnetic relaxation in a ferromagnetic CuII chain complex, induced by a phonon bottleneck effect.

The first slow magnetic relaxation in a ferromagnetic Cu(II) chain compound, Cu(dipic)(OH2)2 (dipicH2 = pyridine-2,6-dicarboxylic acid), induced by a phonon bottleneck effect under a magnetic field of 0.6 T, with a relaxation time of 2.2 s at 2.8 K, was observed.

Confocal Raman microscopic evidence for cyclic water Pentamer, at high temperatures in a supramolecular host of [Cu(cyclam)(N3)2]·4H2O.

Here, we report the existence of a pentameric water cluster in the host framework of [Cu(cyclam)(N3)2]·4H2O, that is stable upto 167 °C, well above the boiling point of water. The pentameric cluster structure embedded in the host framework is evident from the single crystal studies. The high thermal stability is confirmed by TGA and temperature dependent confocal Raman microscopic studies, where loss of water bands is well captured between 167 and 170 °C, besides its existence through SCXRD studies. To the best of our knowledge, this is the first report where temperature dependent confocal Raman microscopic investigation is used to study the stability of water in crystal environment. The study promises that temperature dependent confocal Raman microscopy can be an efficient tool to investigate the existence and stability of small water clusters, precisely in restricted environments.

Ligand directed structural diversity and magnetism in copper(ii)-azido assemblies with isomeric aminopyridines: synthesis, structure, magnetism and theoretical studies.

Four new copper complexes, viz. [{Cu(2-aminopyridine)(N3)2(H2O)}2]n (1), [Cu3(3-aminopyridine)2(N3)6]n (2), [{Cu(3-aminopyridine)(N3)2}2]n (3), and [Cu(4-aminopyridine)2(N3)2]n (4), have been synthesized with isomeric aminopyridines, viz. 2-aminopyridine (2-ap), 3-aminopyridine (3-ap), and 4-aminopyridine (4-ap), to probe the role of ligand and reactant molar ratios in directing the polynuclear assemblage and the associated magnetic properties. Ligand geometry is quite influential as can be seen through the versatile structures formed, viz. a hydrogen bonded layer of µ-1,1 azide bridged Cu dimers in 1; a network of two different types of dimers (Cu1-Cu2 & Cu3-Cu3') involving µ-1,1; µ-1,3; µ-1,1,3; & µ-1,1,3,3 azide bridges in 2; a ladder structure in which µ-1,1 azide bridges form the rungs and µ-1,3 azide bridges form the rails of the ladder in 3; and a 1-D polymer chain involving µ-1,1 azide bridges in 4. Consistent with the bridge geometry, compounds 1 & 2 display ferromagnetic interactions, while 3 & 4 display antiferromagnetic interactions. The rather unexpected antiferromagnetic interactions in 3, in spite of µ-1,1 azide bridged rungs may be due to the crossover near the bridge angle. The ferromagnetic interactions in 1 and 2 are supported by DFT calculations.

Anion directed structural diversity in zinc complexes with conformationally flexible quinazoline ligand: structural, spectral and theoretical studies.

In this paper, we report the synthesis, structure and photophysical studies of four new complexes of conformationally flexible 6-chloro-4-phenyl-2-(pyridin-2-yl)quinazoline ligand (L) with Zn(ii). The coordinating ability of the ligand and geometrical preferences of the resultant complexes are tuned by varying the anion of the metal salt as confirmed by structural and DFT studies. The choice of the metal salt (especially anion) directs the stabilisation of different conformations of the ligand arising out of twisting of the pyridyl ring with respect to the quinazoline ring, resulting in complexes with different nuclearity (monomer/dimer) as well as different coordination geometries (tetrahedral/trigonal bipyramidal/octahedral). Photophysical properties are also found to be tuned due to conformational changes on complexation. DFT studies on the ligand establish the conformationally stable forms as observed in the reported structures.

Significance of weak interactions in imidazolium picrate ionic liquids: spectroscopic and theoretical studies for molecular level understanding.

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.