Abstract
The affinity of crown ethers for metal ion is strongly dependent on the size of the ring of the crown ether. The crown ether-metal ion binding is enhanced in the absence of non-coplanar donor oxygen atoms and electron withdrawing substituents in the crown ether skeleton. The study of absorption of radio frequency radiation by a magnetic nucleus provides useful information regarding structure of a number of organic and inorganic compounds. Small changes were observed in the chemical shift of 1-H in 15C5, 18C6 and, 1-H as well as 2-H, in dibenzo18C6. After formation of the [Metal-Crown ether]Ligand complex, the proton chemical shift δ(-CH2-O- ) shows significant downfield shifts [Δδ(-CH2-O-)= 0.08-0.25 ppm], indicating metal-ligand bond formation. The degree of downfield shift shows the relative strength of the complexes. The 1H-NMR spectrum of dibenzo18C6 shows peaks at, δ1=3.9-4.1 ppm, (16H, 8 -CH2O-), δ2=6.8-7.0 ppm, (8H, aryl -CH-), in CDCl3. The shift of -CH2- signals in complexes from free crown ether unambiguously suggested the coordination of crown ether oxygen of 15C5, 18C6 as well as dibenzo18C6 with thallium ion.
The present paper describes the preparation and characterization of some Tl(I) complexes with 1,4,7,10,13,- pentaoxacyclopentadecane (15C5), 1,4,7,10,13,16,-hexaoxacyclooctadecane (18C6) and 2,3,11,12-dibenzo- 1,4,7,10,13,16,-hexaoxacyclooctadeca-2,11-diene (dibenzo18C6), having five and six donar oxygen atoms respectively. The metal salts used for complexation are salts of nitrophenols. Products were isolated from thallium salts of all the three monoionic ligands, 2-nitrophenol (ONPH), 2,4-dinitrophenol (DNPH) and 2,4,6- trinitrophenol (TNPH) and were chromotographed using TLC. The bonding patterns of complexes were suggested from the studies of elemental analysis, molar conductivity, IR, UV-Vis and 1H-NMR spectral analysis.
