Sanchari Dasgupta

Development of an efficient magnetically separable nanocatalyst: theoretical approach on the role of the ligand backbone on epoxidation capability

Three chiral Schiff base ligands H2L1, H2L2, H2L3 have been synthesized by treating (R)-1,2-diaminopropane separately with 3,5-dichlorosalicylaldehyde, 3,5-dibromosalicylaldehyde and 3,5-diiodosalicylaldehyde, respectively. Three new asymmetric FeIII complexes, namely, FeL1Cl (1), FeL2Cl (2), FeL3Cl (3) have been prepared from their corresponding ligands. The crystal structure of 2 reveals that the complexes are mononuclear in nature. Circular dichroism (CD) studies suggest that the ligands and their corresponding complexes contain an asymmetric center. The catalytic activity of these complexes toward the epoxidation of alkenes has been investigated in the presence of iodosylbenzene (PhIO), in two solvents CH3CN and CH2Cl2. The epoxide yield suggests that the order of their catalytic efficiency is 3 > 2 > 1. This trend as well as the role of substitution on the ligand backbone on alkene epoxidation has also been confirmed by density functional theory (DFT) calculations. For further adaptation, we attached our most efficient homogeneous catalyst, 3, with surface modified magnetic nanoparticles (Fe3O4@dopa) and thereby obtained the new magnetically separable nanocatalyst Fe3O4@dopa@FeL3Cl. This catalyst has been characterized and its olefin epoxidation ability investigated in similar conditions to those used for homogeneous catalysts. The enantiomeric excess of the epoxide yield reveals the retention of chirality of the active site of Fe3O4@dopa@FeL3Cl. The catalyst can be easily recovered by magnetic separation and recycled several times without significant loss of its catalytic activity.

A Deep Insight into the Photoluminescence Properties of Schiff Base CdII and ZnII Complexes

A tridentate N,N,O donor ligand 2,4-dichloro-2-[(2-piperazine-4-yl-ethylimino)-methyl]-phenol (HL) was designed, and eight new ZnII and CdII complexes, namely, [Zn(LH)(SCN)2] (1), [Zn(LH)(N3)2] (2), [Zn(LH)(NO2)2] (3), [Zn(LH)(dca)(OAc)] (4), [Cd2(LH)2(SCN)4] (5), [Cd(LH)(N3)2] (6), [Cd(LH)(NO2)2] (7), and [Cd(LH)(dca)(OAc)] (8) [where dca = dicyanamide anion] were synthesized. Five of them (1, 2, 4, 5, 7) were structurally characterized through single-crystal X-ray diffraction analysis. H-Bonding interactions are found to be the major stabilizing factor for crystallization in the solid state. Experimental and computational studies were performed in cooperation to provide a rationalization of the photoluminescence properties of those complexes. The quantum yields are anion-dependent, with enhanced efficiencies in the following order: LH < Cd-SCN(5) < Cd-dca(8) < Cd-N3(6) < Cd-NO2(7) < Zn-dca(4) < Zn-N3(2) < ZnNO2(3) < ZnSCN(1). By using quantum chemical calculations we rationalized the above trends. Moreover, the diverse lifetimes observed for those eight complexes were also quantitatively explained by considering the subtle competition between different photo-deactivation pathways.

Portraying the role of halo ligands and the auxiliary part of ligands of mononuclear manganese(III)-Schiff base complexes in catalyzing phospho–ester bond hydrolysis

Four mononucleating Schiff base ligands, namely HL1, HL2, HL3 and HL4, were prepared via condensation between 2-hydroxybenzaldehyde and 2-morpholinoethanamine, 2-(piperazin-1-yl)ethanamine, 2-(piperidin-1-yl)ethanamine and 2-(pyrrolidin-1-yl)ethanamine, respectively. Then, seven mononuclear manganese(III) complexes were synthesized using the above-mentioned ligands. Complexes 1–3 were prepared with ligand HL1 by using chloride, bromide and iodide salts of manganese(II), respectively. On the other hand, complexes 4, 5, 6 and 7 were prepared by reaction of manganese chloride followed by sodium thiocyanate with ligands HL2, HL3, HL4, and HL1, respectively. All the complexes were characterized by using the usual physicochemical techniques and their solid state structures were obtained from single crystal X-ray analysis. The phosphatase-like activity of these complexes was studied in a 97.5% (v/v) N,N-dimethylformamide–water mixture using the disodium salt of 4-nitrophenylphosphate (4-NPP) as a model substrate to evaluate the role of halo-anions and the auxiliary part of the ligand backbone in the phosphatase like activity. Detailed experimental findings proved that complex 2 is the most active catalyst among all seven complexes and the complex bearing a morpholine ring is the most active catalyst among complexes 4–7.