Suman K Roy

Introducing a New Azoaromatic Pincer Ligand. Isolation and Characterization of Redox Events in Its Ferrous Complexes

The isolation and complete characterization of a new bis-azoaromatic ligand, 2,6-bis(phenylazo)pyridine (L), are described, and its coordination to iron(II) is reported. A pseudo-trigonal-bipyramidal mixed-ligand complex of iron(II), FeLCl2 (1), and a homoleptic octahedral iron complex, mer-[Fe(L)2]ClO4 [2]ClO4, have been synthesized from L and FeCl2 or hydrated Fe(ClO4)2, respectively, in boiling methanol. Determination of the X-ray crystallographic structure together with magnetic data (≈ 5.06 μB) and Mössbauer analysis of 1 established a high-spin Fe(II) complex ligated by one neutral 2,6-bis(phenylazo)pyridine ligand. The X-ray crystallographic structure (showing dN-N > 1.30 Å), Mössbauer data, and magnetic susceptibility measurements (≈ 1.65 μB) as well as a nearly isotropic EPR signal with only a small metal contribution at g = 1.968, on the other hand, suggest a low-spin Fe(II) complex with a one-electron-reduced radical ligand coordination in [2]ClO4. The ligand and the metal complexes have well-behaved redox properties, with the ligand(s) functioning as the redox-active site(s) responsible for redox events. The uncoordinated ligand, L, displays a reversible one-electron wave at -1.07 V and a quasi-reversible wave at -1.39 V. The partially reduced ligand L(•-) shows a single-line EPR spectrum at g = 2.001, signifying that L(•-) is a free radical. While complex 1 shows a reversible reduction at -0.08 V and an irreversible cathodic response at -0.98 V, the bis-chelate [2]ClO4 undergoes a reversible one-electron oxidation at 0.54 V and three successive reversible one-electron reductions at -0.18, -0.88, and -1.2 V, all occurring at the ligands without affecting the metal ion oxidation state. The electronic structures of the parent monocationic complex [2](+) and its oxidized and reduced forms, generated by exhaustive electrolyses, have been characterized by using a host of spectroscopic techniques and density functional theory (DFT). It is found that the 2,6-bis(phenylazo)pyridine ligand (L) is truly redox noninnocent and is capable of coordinating transition-metal centers in its neutral ([L](0)), monoanionic monoradical ([L(•)](-)), and dianionic diradical ([L(••)](2-)) forms.

Aerial oxidation of protonated aromatic amines. Isolation, X-ray structure, and redox and spectral characteristics of N-containing dyes.

This work reports the results of our investigation on the aerial oxidation of aromatic amines that are promoted by protic acid. While primary aromatic amines produce substituted phenazines as major products, N-phenyl-o-phenylenediamine produces polycyclic aromatic heterocycles like azaacene and secondary and tertiary amines give exclusively the dyes containing a triphenylmethane moiety. Isolation of the compounds and the effects of substitutions on the aromatic rings have been investigated. In this context, plausible reaction steps that are involved have been discussed. Single-crystal X-ray structure analyses of the representative compounds are solved to authenticate their formation. In almost every case, a high degree of delocalization of electron was noted. The compounds have been characterized thoroughly and show rich spectral properties. For example, the phenazine molecules exhibited absorption peaks between 475 and 605 nm because of the charge-transfer transition from the amine and tricyclopyrazine moiety. Their acidochromic and solvatochromic behaviors, which are supported by theoretical calculations, are investigated. The polycyclic azacene molecule exhibits strong absorption in the visible region and fluoresces with high quantum yield. The phenazine dyes undergo a quasi-reversible reduction at a low cathodic potential that varies linearly as a function of Hammetts constant.

Redox noninnocence in coordinated 2-(arylazo)pyridines: steric control of ligand-based redox processes in cobalt complexes.

A series of cobalt complexes of ligands based on the 2-(arylazo)pyridine architecture have been synthesized, and the precise structure and stoichiometry of the complexes depend critically on the identity of substituents in the 2, 4, and 6 positions of the phenyl ring. The 2-(arylazo)pyridine motif can support either Co(II) complexes with neutral ligands, Co(II)Cl2(L(a))2 (1), Co(II)Cl2(L(c))2 (3), [Co(II)Cl(L(b))2]2(PF6)2 (5[PF6]2), or Co(III) complexes of reduced 2-(arylazo)pyridine ligand radical anions, L(•-), Co(III)Cl(L(b•-))2 (2), Co(III)Cl(L(c•-))2 (4), and Co(III)Me(L(b•-))2 (6). All three members of the latter class are based on approximately trigonal-bipyramidal CoX(L(•-))2 architectures [L = 2-(arylazo)pyridine] with two azo nitrogen atoms and the X ligand (X = Cl or Me) in the equatorial plane and two pyridine nitrogen atoms occupying axial positions. Density functional theory suggests that the electronic structure of the Co(III) complexes is also dependent on the identity of X: the strong σ-donor methyl gives a low-spin (S = 0) configuration, while the σ/π-donor chloro gives an intermediate-spin (S = 1) local configuration. In certain cases, one-electron reduction of the Co(II)X2L2 complex leads to the formation of Co(III)X(L(•-))2; i.e., reduction of one ligand induces a further one-electron oxidation of the metal center with concomitant reduction of the second ligand.

Mesomorphic properties and orientational order parameter of 4-pentyl cyclohexyl-4-(4-propyl cyclohexyl) benzoate from X-ray diffraction studies

Abstract The mesogen 4-pentyI cyclohexyl-4-(4-propyl cyclohexyl) benzoate, molecular formula C27H42O2, has been investigated at different temperatures using X-ray and texture studies. For X-ray studies an arrangement for taking X-ray photographs at different temperatures has been designed and fabricated. In addition to the nematic phase the mesogen exhibits two smectic phases. On the basis of microscopic investigation and X-ray studies the two smectic phases exhibited have been identified as the SmE and SmB phases. From X-ray patterns, the average intermolecular distances and apparent molecular length/layer thickness for the different mesomorphic phases have been determined as a function of temperature. Orientational order parameters (P2) and (P4) of the sample ordered by a magnetic field have been determined in the SmB phase.

Double CaromH Activation Associated with Etheral Oxygen Insertion to Phenazine Architecture in Oxidisable Ruthenium(III) Complexes: A Mechanistic Insight

Three examples of unusual double aromatic CH bond activation associated with insertion of etheral oxygen atom to phenazine architecture in Ru(III) complexes are reported. The chemical transformations have led to the formation of new Ru(IV) complexes with angular pentacyclo heterocyclic ligands. A mechanistic investigation indicates that the overall process is a combination of successive steps involving air (O2 ) and H2 O.

Correlation between weather and weather-related tweets — A preliminary study

Through this preliminary work, we are trying to understand the humans sentiment regarding climate change. We collect tweets containing words like climate, nature and environment. We analyze the data to find out if there is any correlation between weather and weather-related tweets.

CCDC 982580: Experimental Crystal Structure Determination

Related Article: Pradip Ghosh, Subhas Samanta, Suman K Roy, Sucheta Joy, Tobias Kramer, John E. McGrady, and Sreebrata Goswami|2013|Inorg.Chem.|52|14040|doi:10.1021/ic4018079