Use of 155Gd, 151Eu, 166Er Mössbauer spectroscopy to characterize heterodinuclear Ln–Ln′ complexes

Abstract

Use of 155Gd Mössbauer spectroscopy allows a straightforward characterization of heterodinuclear Ln-Ln′ complexes (LLnLn′ (NO3)3·(H2O)2) with a tripodal ligand L, possessing two different N4O3 and O3O3 coordination sites. Thanks to the isomer shift value, the location of the GdIII ion is confirmed; the Gd atom in the Gd–Ln′ series (Ln′ = Ce, Nd, Eu) occupies the inner N4O3 site with a eight-coordination (N4O3 + O), but on the other hand the Gd atom in the Ln–Gd series (Ln = Dy, Er, Yb) resides in the outer O3O3 site with a ten-coordination (O3O3 + O2 + O2). The smaller isomer shift values for the former indicate that coordination of the basic nitrogen atoms enhances the 6s orbital population. With the help of 151Eu Mössbauer spectroscopy, we demonstrate that the Gd–Eu entity is a genuine heterodinuclear complex, in which the GdIII ion is located in the inner site and the EuIII ion in the outer oxygenated site. This result highlights the feasibility of our synthetic process described earlier to introduce in a heterodinuclear complex two consecutive ions of the periodic table. And the slow paramagnetic relaxation observed in the 166Er Mössbauer spectrum of the Er–Gd complex confirms presence of a magnetic interaction in the genuine Er–Gd complex.