Absolute configurational assignment of self‐organizing asymmetric tripodal ligand‐metal complexes

Abstract

The solution configuration of labile coordination complexes may be difficult to determine, even in cases in which the solid state structure is known. We have previously synthesized a series of chiral ligands which form pseudo-C 3 -symmetric complexes with Zn II and Cu II salts that possess an available electrophilic coordination site. Molecular modeling of Zn II complexes of the chiral ligand N,N-bis[(2-quinolyl)methyl]-1-(2-pyridyl)ethanamine (␣-MeBQPA) showed that the spatial arrangement of the heterocyclic arms is controlled by a substituent on one methylene arm, resulting in the adoption of an enantiomeric conformation displaying a propeller-like asymmetry. In this paper we report the application of the exciton chirality method to the determination of the conformation of asymmetric metal-ligand complexes in solution. There is a good correlation between the predicted and the observed Cotton effects, demonstrating that the geometry in solution closely resembles that predicted by computational simulations and those obtained by X-ray crystallographic studies of metal complexes with racemic and enantiomerically pure ligands. The X-ray crystallographic structure of the first optically pure complex in this series is reported. Chirality 9: 616-622, 1997.

A theoretical study on the exciton circular dichroism of propeller‐like metal complexes of bipyridine and tripodal tris(2‐pyridylmethyl)amine derivatives

“…We have further extended the study to the Cu(II) and Zn(II) complexes of tetradentate N 4 -tripodal ligands related to a-substituted tris ( 16,17 that the complexes under consideration here predominantly display trigonal bipyramidal (tbp) geometry with the pyridine or quinoline moieties binding to the metal ion as monodentate ligands. The pyridine or quinoline chromophores in the complexes adopt the propeller-like arrangement that resembles the structure of the corresponding cis bis-and tris-bipyridyl octahedral complexes.…”

Supramolecular Detection of Metal Ion Binding: Ligand Conformational Control of Cholesteric Induction in Nematic Liquid Crystalline Phases

“…The structure of the related complex [Cu II ((R)-3)(CH 3 CN)](O 2 CF 3 ) 2 was previously established by X-ray crystallography ( Figure 5), circular dichroism, UV/Vis spectroscopy, and elemental analysis. [9] The complex showed a trigonal bipyramidal (tbp) coordination geometry for the metal ion in the solid state; the solution spectra were consistent with this assignment. When the metal ion is tbp, the ligand adopts a C 3 conformation, which orients the two quinoline moieties in a highly asymmetric manner, with projection angle of 128.…”

“…[8] From the CD spectra of the complexes we assigned the absolute sense of the orientation of the quinoline rings in solution. [9] Complexes of several metal ions were studied; it was found that only metals that bind the ligand in a trigonal bipyramidal coordination geometry (Zn II , Cu II ) engendered a C 3 -like conformation ( Figure 2) in the ligand and thus gave the propeller twist and large CD amplitudes. Metal ions forming octahedral complexes with 3 (Fe II , Cd II ) enforced a distorted ligand conformation (C s , Figure 2), no twist, and low amplitude CD spectra.…”

Syntheses and structures of chiral tri- and tetranuclear Cd(II) clusters with luminescent and ferroelectric properties

“…Solvents were freshly distilled over appropriate drying reagents under a N 2 atmosphere. [16]. The chiral Schiff base ligands were prepared in solution and directly used without further separation (Scheme 1).…”