Pradip Paul

Reduction of Me8[14]diene·2HClO4 (L·2HClO4) afforded three isomeric ligands (LA, LB and LC), among which LC underwent cyanoethylation with excess acrylonitrile to form the bis-cyanoethyl derivative (LCX). Reaction of LCX with zinc(II) chloride yielded the six-coordinate complex [Zn(LCX)Cl2], which subsequently underwent axial ligand substitution with KSCN, KNO3, NaNO2, KBr and KI to produce a series of octahedral zinc(II) complexes, [Zn(LCX)(X)2] (X = NCS, NO3, NO2, Br or I). All the Zn(II) synthesised complexes were characterized using various analytical and spectroscopic techniques. Their antibacterial activity was evaluated against four selected bacterial strains and most of the complexes exhibited good antibacterial activity against the tested bacteria.

Dihydroperchlorate salt of a 14-membered tetraazamacrocycle, Me8[14]diene·2HClO4 (L·2HClO4) was synthesized by the condensation of 1,2-diaminopropane with acetone in the presence of a stoichiometric amount of perchloric acid. LB, one of the three isomers (L­­A, LB and LC: isolated from the reduced product of the ligand salt (L·2HClO4), on reflux with excess amount of acrylonitrile produced corresponding white solid product, LBX (trans-N4,N11-bis(2-cyanoethyl) 2,9-C-meso-3,5,7,7,10,12,14,14-tetraazacyclotetradecane). The reactions of LBX with vanadyl acetylacetonate followed by addition of few drops of vinyl cyanide yielded the pale green product, [VO(LBX)(acac)](ClO4)2. The axial substitution reactions on [VO(LBX)(acac)](ClO4)2 with NCS–, NO3–, NO2–, Cl–, Br– and I– furnished different coloured axial substitution products with different geometries. The structural features of the complexes were confirmed using IR, NMR and UV-Vis spectroscopy, revealing their octahedral geometry. Antibacterial studies showed selective activities against Gram-positive and Gram-negative bacteria, suggesting potential biomedical applications.

Interaction of tet-a (an isomeric ligand of Me₆[14]ane) with an excess of acrylonitrile yielded an N-pendent derivative, tet-ax in which two cyanoethyl groups were attached on less crowded two trans-N atoms. Reactions of nickel(II) acetate tetrahydrate followed by subsequent addition of NaClO₄·6H₂O, copper(II) perchlorate hexahydrate and cobalt(II) acetate tetrahydrate followed by the addition of HCl [in case of cobalt(III) complex] with tet-ax produced four coordinated square planar orange [Ni(tet-ax)](ClO₄)₂, six coordinated octahedral red [Cu(tet-ax)(ClO₄)₂] and six coordinated green trans-[Co(tet-ax)Cl₂]Cl complex, respectively. The axial substitution reactions on [Cu(tet-ax)(ClO₄)₂] with MX (M = K/Na, X = NCS, NO₃, NO₂, Cl, Br, or I) resulted in six coordinated octahedral axial substitution products, blue [Cu(tet-ax)(NCS)(ClO₄)], [Cu(tet-ax)(NO₃)(H₂O)]ClO₄, and [Cu(tet-ax)(NO₂)(H₂O)]ClO₄, violet [Cu(tet-ax)Cl(H₂O)]ClO₄ and [Cu(tet-ax)Br(H₂O)]ClO₄ and green [Cu(tet-ax)I(H₂O)]ClO₄ respectively. All the newly formed compounds have been characterized by using different modern techniques. The antimicrobial activities of this new N-pendent derivative tet-ax and its metal complexes have been investigated against different bacteria and fungi.

Condensation reactions involving various ketones and amines formed noncyclic ligands denoted as L^I, L^II, L^III, and L^IV. Ethylenediamine, when reacted with acetophenone, benzoylacetone (in the presence of 70% HClO₄), and benzophenone, resulted in the following noncyclic ligands: (E,E)-N,N-bis(1-phenylethylidene)ethylenediamine (L^I), bis(1-3-hydroxy-3-phenylbut-2-ene-ylidene) (L^II) and (E,E)-N,N-bis(1,1-diphenylmethylidene)ethylenediamine (L^III), respectively. The reaction of benzophenone with 1,3-diaminopropane in a 1:1 ratio in a methanolic solution also led to the synthesis of a noncyclic ligand, (E,E)-N,N-bis(1,1-diphenylmethylidene)propylenediamine (L^IV). All the synthesized noncyclic ligands, except L^II, undergo decomposition during complexation, reverting to the initial ketones and amines. In contrast, L^II exhibits remarkable stability and can form square planar complexes with Ni(II), Cu(II), and Co(II) salts. Additionally, the Co(II) complex can convert into a six-coordinated Co(III) complex, [CoL^II(H₂O)₂](NCS), when it reacts with KNCS. All these ligands and derived metal complexes were characterized, and their antimicrobial properties were evaluated against the selected fungi and bacteria.

A dihydroperchlorate salt of octamethyl derivative of 14-membered tetraazamacrocycle, Me8[14]diene·2HClO4 (L·2HClO4), was formed by the condensation of 1,2-diamino propane with acetone in the presence of a quantitative amount of perchloric acid, which on extraction with chloroform at pH above 12 yielded free ligand (L). The interaction of rhodium(III) trichloride trihydrate and platinum(II) chloride with free ligand L produced six-coordinated octahedral orange-red complex, cis-[RhLCl2]Cl and four-coordinated square-planar yellow complex, [PtL]Cl2, respectively. Axial substitution reactions on [RhLCl2]Cl with KX (X = NO3, Br or I) and NaNO2 afforded six-coordinated deep brown products [RhLY2]Y (Y= NO3, Br, I or NO2). The ligand and metal complexes were characterized based on analytical, molar conductivity, spectroscopic and magnetochemical data. The antimicrobial activities of the concerned ligand and its complexes have been explored against some selected bacteria and fungi.

Yellow-orange crystalline quinolinium fluorochromate (QFC) is easily prepared in a nearly quantitative yield by the interaction of quinoline with CrO3 and hydrofluoric acid in 1 : 1.5 : 1 molar ratio. The reagent is stable. Compared with pyridinium fluorochromate (PFC), the new reagent is more soluble in organic solvents and less acidic. QFC in CH2Cl2 readily oxidizes primary, secondary, and allylic alcohols to the corresponding carbonyls, benzoin to benzil, and anthracene and phenanthrene to anthraquinone and 9,10-phenanthrenequinone, respectively. Oxidations work well also in a variety of sensitive environments, e.g. isopropylidene functionality and trimethylsilyl ethers. Organic sulfides are transformed to sulfoxides at room temperature. The facile oxidation of triphenylphosphine to triphenylphosphine oxide by QFC in CH2Cl2 or CH3CN provides a clear evidence for an oxygen-transfer reaction. The reduced product of QFC, isolated after such reactions, has been ascertained to be C9H7NH[CrO2F], a chromium(IV) species. The advantages of QFC have been highlighted.