Equilibria in complexes of N-heterocyclic molecules. Part 29. An electron spin resonance study of some N-heterocyclic complex ions of silver(II)

Abstract

A critical assessment of the e.s.r. parameters for complex compounds of the silver(II) ion with the N-heterocyclic donors pyridine, 2,2′-bipyridyl, and 1,10-phenanthroline is presented. In previous reports, nitric acid has often been used as an ‘inert’ solvent; this is wrong. Protons and silver(II) ions compete for the ligands, equilibria being fairly rapidly established. Species studied in nitric acid solutions made from solid compounds of silver(II) are usually not those present in the pure solid. Another important difference in the present investigation is in the assignment of the nitrogen superhyperfine coupling constants. It is now well established that A_∥^N and A_⊥^N cannot be immediately obtained from the e.s.r. spectra. This paper also introduces the use of a new line-sharpening device, suitable for obtaining extremely well resolved e.s.r. spectra of solids.