Theoretical study of integrated crown ethers and their complexes with some transition and lanthanide ions

الملخص EN

Geometrical parameters, ultraviolet and vibrational frequencies, relative stabilities, and heat of association of the six crown ethers (١٢O٤, ١٢N٤, ١٢S٤, ١٢O٢N٢, ١٢O٢S٢, ١٢N٢S٢) were calculated by HF/STO-٦G and HF/٦-٣١G level of theory.

The energies were calculated by single-point MP٢ method using polarized ٦-٣١G basis functions.

The potential energy surface and HOMO-LUMO of these ligands indicate a remarkable change in electron density of ١٢O٤ when nitrogen and sulfur atoms replaced the oxygen atoms which result in a major change in their ion selectivity toward transition (Co٢+ , Ni٢+ , Cu٢+ , Rh٢+ , and pd٢+ ) and lanthanide (Nd٢+ , Sm٢+ , Eu٢+ , Tm٢+ , Yb٢+ ) ions .

The free ligands ١٢N٤ and I٢N٢S٢ were unstable in gas phase through geometry optimization but they are stable through complexation calculations.

The heats of association with A-type and B-type ions were calculated by MMplus.

In aqueous solution the ١٢N٤ and ١٢S٤ showed a high selectivity for Pd٢+, Cu٢+ions while the ligand ١٢O٤ preferred to select Pd٢+ and Rh٢+ ions.

The six ligands showed the same tendency for the lanthanide metal ions in the gas phase but they behave in a different manner in the aqueous phase.

The theoretical IR vibrational spectra showed that Pd-N stretching, Pd-O stretching, and Pd-S stretching have a similar values within the range ٦٠٣-٦١٦ cm-١.