Trinuclear to Dinuclear: A Radii Dependence Lanthanide(III) Self-Assembly Coordination Behavior of an Amide-Type Tripodal Ligand

Lanthanide nitrate complexes with the heptadentate ligand L (6-[2-(2-(diethylamino)-2-oxoethoxy)ethyl]-N,N,12-triethyl-11-oxo-3,9-dioxa -6,12-diazatetradecanamide), [Ln2L(NO3)6] (Ln = La, Nd, Sm, Eu, Ho), have been prepared and characterized. The X-ray crystallographic studies show that, in [La2L(NO3)6(H2O)]·H2O (1), two complex cations [LaL(H2O)]3+ are linked by a hexanitrato anion [La(NO3)6]3- and form a trinuclear cation. In [Nd2L(NO3)6(H2O)]·CHCl3·1/2CH3OH·1/2H2O (2), one complex cation [NdL(H2O)]3+ and a hexanitrato complex anion [Nd(NO3)6]3- are linked by a bridging NO3- to form a dinuclear complex. In both complexes, the bridging nitrate is an unusual tetradentate ligand. The metal ions are 12-coordinated in hexanitrato anions and 10-coordinated in complex cations. The chainlike supramolecular structures of La3+ complex are parallel and have no hydrogen bonds in between, while, in the Nd3+ complex, a chiral cavity is formed by hydrogen bonds between two adjacent supramolecular chains. These influences are further investigated by assessing the separation efficiency of L and 1H NMR spectra of its lanthanide nitrate mixtures in solution.