Macrocyclic ligand design. X-Ray, DFT and solution studies of the effect of N-methylation and N-benzylation of 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane on its affinity for selected transition and post-transition metal ions

Abstract

Potentiometric titration in 95% methanol (I = 0.1 mol dm Ϫ3 , Et 4 NClO 4 ) has been employed to investigate the effect of N-methylation and N-benzylation of 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane 1 on the binding of all three rings to cobalt(), nickel(), copper(), zinc(), cadmium(), silver() and lead(). The results show that enhanced selectivity for silver() is exhibited by the di-N-benzylated derivative 3 while the analogous dimethylated derivative 2 discriminates for both silver() and lead(). The crystal structures of [Ag(1)]PF 6 , [Ag(2)]PF 6 , [Ag (3)]PF 6 and [Pb(1)(NO 3 ) 2 ] have been determined. In the silver complexes the NH hydrogens of 1 and the N-methyl and N-benzyl substituents of the dialkylated derivatives 2 and 3 were found to lie on the same side of the mean donor planes of the co-ordinated macrocycles ('cis' arrangements). Density functional theory has been employed to model the silver complexes in both their energy-minimised 'cis' and 'trans' configurations. In accordance with the X-ray evidence, the calculations predict that the 'cis' arrangement is the more stable in each case. The crystal structure of the lead complex of 1 shows a 'trans' arrangement of its NH groups.

Lead(II) Complexes of Lateral Macrobicyclic Receptors That Incorporate a Crown Moiety and a Pyridine Head Unit

“…[40] The protonation constants determined for L 2 and L 8 are lower than those reported for the parent crown ether 4,13-diaza- [18]crown-6 (log K 1 = 9.40 and log K 2 = 7.47 in 95 % methanol, I = 0.1  Et 4 NClO 4 , 25°C). [41] This is in accordance with previous observations in which a diminution of the amine basicity has been observed upon N-alkylation of oxa-aza crown ligands. [42] Both L 7 and L 8 show lower protonation constants than the parent receptors L 1 and L 2 .…”

Physicochemical and Biological Characterization of Transition Metal Complexes with a Nitrogen Donor Tetra-dentate Novel Macrocyclic Ligand

“…It is well known that the chemical properties and structure of the partially or fully N-functionalized macrocyclic compounds are distinctly different from those of the unsubstituted ones [1,2]. An investigation of metal complexation studies across a range of related ligands has provided a useful background on which to base further ligand design.…”

Synthesis, FT-Raman, FT-IR, NMR spectroscopic characterization and antimicrobial activity of new mixed aza-oxo-thia macrocyclic compounds

“…For decades, the design and synthesis of macrocyclic compounds with hemo and hetero-multi-donor center have constituted one of the largest areas of research in organic and coordination chemistry [1][2][3][4][5][6][7][8][9]. Nature due to structural impact prefers certain macrocyclic derivatives for many fundamental biological functions, such as photosynthesis, storage and transport of oxygen in mammalian and other respiratory systems.…”