Variation of water exchange dynamics with ligand structure and stereochemistry in lanthanide complexes based on 1,4-diazepine derivatives

Complexes of Gd, Eu and Yb(III) have been prepared with a series of heptadentate ligands related to the parent complex AAZTA, based on the 6-methyl-6-aminoperhydrodiazepine moiety. For (RR) and (RS)-diastereoisomers of a di-glutarate ligand, solution NMR studies revealed the presence of two major species that undergo water exchange rates at Gd differing by a factor of six. Comparison of solution hydration states for Eu(III) complexes reveals that each complex possesses two bound water molecules. The absence of a good correlation of ¹H NMR pseudo-contact shifts for Eu and Yb analogues is suggested to arise from a change in hydration state between Eu and Yb.