Synthesis and characterisation of silver, zinc and cadmium compounds with an N3O2 Schiff base macrocycle: the crystal and molecular structures of the silver(I) and cadmium(II) complexes

Synthesis and Characterisation of the Cd(II) Complex of a Hexadentate(N4O2) Schiff Base Ligand; IR, NMR and Theoretical Studies

A new Cd(II) complex, Cd(L22pysa), prepared from the template condensation of a previously known ligand N(CH2CH2NH2)2(CH2C5H4N), (L22py), salicylaldehyde and [Cd(NO3)2].4H2O in equimolar ratio, has been characterised by IR and variable temperature 1H NMR and 13C NMR spectra. The gas-phase molecular structure of this complex was also studied by ab initio Hartree–Fock and DFT/B3LYP methods.

Insights into Thiol-Aromatic Interactions: A Stereoelectronic Basis for S-H/π Interactions

Thiols can engage favorably with aromatic rings in S-H/π interactions, within abiological systems and within proteins. However, the underlying bases for S-H/π interactions are not well understood. The crystal structure of Boc-l-4-thiolphenylalanine tert-butyl ester revealed crystal organization centered on the interaction of the thiol S-H with the aromatic ring of an adjacent molecule, with a through-space Hthiol···Caromatic distance of 2.71 Å, below the 2.90 Å sum of the van der Waals radii of H and C. The nature of this interaction was further examined by DFT calculations, IR spectroscopy, solid-state NMR spectroscopy, and analysis of the Cambridge Structural Database. The S-H/π interaction was found to be driven significantly by favorable molecular orbital interactions, between an aromatic π donor orbital and the S-H σ* acceptor orbital (a π → σ* interaction). For comparison, a structural analysis of O-H/π interactions and of cation/π interactions of alkali metal cations with aromatic rings was conducted. Na+ and K+ exhibit a significant preference for the centroid of the aromatic ring and distances near the sum of the van der Waals and ionic radii, as expected for predominantly electrostatic interactions. Li+ deviates substantially from Na+ and K+. The S-H/π interaction differs from classical cation/π interactions by the preferential alignment of the S-H σ* toward the ring carbons and an aromatic π orbital rather than toward the aromatic centroid. These results describe a potentially broadly applicable approach to understanding the interactions of weakly polar bonds with π systems.

Synthesis and spectral characterization of 14- and 16-membered tetraazamacrocyclic Schiff base ligands and their transition metal complexes and a comparative study of interaction of calf thymus DNA with copper(II) complexes

14 and 16 membered Schiff base macrocyclic ligands, 7,14-dimethyl-5,12-di(N-amino)-2-methylphenyl-1,4,8,11-tetraaza-cyclotetradecane-4,7,11,14-tetraene (L(1)) and 8,16-dimethyl-6,14-di(N-amino)-2-methylphenyl-1,5,9,13-tetraaza-cyclohexadecane-5,8,13,16-tetraene (L(2)) were synthesized by condensation reaction between 2'-methyleacetoacetanilide and aliphatic diamines. The metal complexes of the types, [ML(1)](NO(3))(2) and [ML(2)(NO(3))(2)] [M = Co(II), Ni(II), Cu(II) and Zn(II)] were prepared by interaction of ligands, L(1) or L(2) with hydrated metal(II) nitrates. The ligands and their complexes were characterized by elemental analysis, IR, (1)H and (13)C NMR, EPR, UV-Vis spectroscopy, magnetic susceptibility, conductivity measurements and ESI-mass spectral studies. The results of elemental analyses, ESI-mass and conductivity measurements confirmed the stoichiometry of ligands and their complexes while the characteristic absorption bands and resonance peaks in IR and NMR spectra confirmed the formation of ligand frameworks around the metal ions. The square planar geometry for complexes derived from ligand L(1) and octahedral environment for complexes derived from ligand L(2) with distortion in Cu(II) complex have been confirmed on the basis of results of electronic and electron spin resonance spectral studies and magnetic moment measurements. Absorption and fluorescence spectral studies revealed different binding mode for complex, [CuL(1)](NO(3))(2) as compared with [CuL(2)(NO(3))(2)] on interaction with calf thymus DNA.

Characterisation of novel macroacyclic hexadentate (N4O2 and N2O4) Schiff base ligands and their zinc(II), copper(II) and cobalt(II) complexes, with ligands derived from reduction

The macrocyclic, hexadentate (N4O2 and N2O4) Schiff base ligands, 1,2-bis(2′-nitrophenoxy)benzene, 1,2-bis (2′-nitrophenoxy)-4- t-butylbenzene), 1,2-bis(2′-aminophenoxy)benzene and 1,2-bis(2′-aminophenoxy)-4- t-butyl-benzene have been synthesised, together with macroacyclic hexadentate ligands formed from their reduction. Zinc(II), copper(II) and cobalt(II) complexes of the Schiff base ligands have also been prepared and all compounds have been characterised by spectroscopy and elemental analysis.