Premium
In Search for Mononuclear Helical Lanthanide Building Blocks with Predetermined Properties: Triple‐stranded Helical Complexes with N,N,N',N' ‐tetraethylpyridine‐2,6‐dicarboxamide
Author(s) -
Renaud Fabien,
Piguet Claude,
Bernardinelli Gérald,
Bünzli JeanClaude G.,
Hopfgartner Gérard
Publication year - 1997
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19970031014
Subject(s) - isostructural , lanthanide , crystallography , ligand (biochemistry) , chemistry , coordination sphere , amide , paramagnetism , trigonal prismatic molecular geometry , acetonitrile , ion , pyridine , stereochemistry , crystal structure , octahedron , medicinal chemistry , receptor , physics , biochemistry , organic chemistry , chromatography , quantum mechanics
The ligand N,N,N',N' ‐tetra‐ethylpyridine‐2,6‐dicarboxamide ( L 9 ) reacts with trivalent lanthanide ions (Ln III ) to give stable mononuclear triple‐stranded helical complexes [Ln( L 9 ) 3 ] 3+ (Ln = La to Lu). The crystal and molecular structures of [La( L 9 ) 3 ](ClO 4 ) 3 .2.5C 2 H 5 CN ( 8 ) and [Eu( L 9 ) 3 ](TfO) 3 .2THF ( 9 ) show that the three ligand strands are each meridionally tricoordinated to produce a pseudo‐tricapped trigonal prismatic arrangement of the nine donor atoms (six amide O and three pyridine N) around Ln III . The distortions in the La III coordination sphere of 8 are more significant than for Eu III in 9 , and the photophysical studies on Eu‐doped (2%) La, Gd, and Lu complexes confirm a better structural match of L 9 for the heavy Ln III ions. The separation of contact and pseudo‐contact contributions to the induced lanthanide paramagnetic NMR shifts in [Ln( L 9 ) 3 ] 3+ shows that the triple‐helical structure is maintained in acetonitrile, but a minor structural change relative to that observed in the solid state occurs between Tb III and Er III leading to two distinct isostructural series for Ln = La‐Tb and Ln = Er‐Lu. The origin of this effect together with its consequences for the dynamic helical ( P → M ) interconversion and stability of [Ln( L 9 ) 3 ] 3+ in solution are discussed. A detailed investigation of the emission properties of [Ln( L 9 ) 3 ] 3+ (Ln = Eu, Tb) shows that mixed pyridine‐carboxamide ligands can be used to simultaneously optimize the structural and photophysical properties in mononuclear triple‐helical lanthanide building blocks.