Complexes of silver(i) ions with tetrapyrrolidinyl- and tetramorpholinyl-PNP-lariat ethers in acetonitrile and methanol solutions

Abstract

This work concerns the investigation of stability constants of silver(I) ions with the tetrapyrrolidinyl-PNP-lariat ether L1 in acetonitrile solution and tetramorpholinyl-PNP-lariat ether L2 in acetonitrile and methanol solutions. The new tetramorpholinyl-PNP-lariat ether L2 was synthesized on the basis of the procedure described in a previous publication. Stability constants of complexes with silver ions were determined using a simple potentiometric titration. Furthermore, NMR spectra were obtained to investigate how the complexation of silver(I) ions by the investigated macrocyclic ligand occurs. Spectrometric data analyses and potentiometric measurements indicate that complexation of Ag⁺ involves participation of the endocyclic nitrogen atom of the cyclophosphazene ring and polyether oxygen donors. As regards L1 the stability of the obtained complex is influenced by pyrrolidinyl groups. On the other hand, L2 includes the morpholinyl subunits attached to the exocyclic P atom, having in their structure the oxygen atom, which pulls out the electrons of the cyclophosphazene ring and thereby destabilizes the formation of a coordination system.