Solution and structural investigations of ligand preorganization in trivalent lanthanide complexes of bicyclic malonamides.
This report describes an investigation into the coordination chemistry of trivalent lanthanides in solution and the solid state with acyclic and preorganized bicyclic malonamide ligands. Two experimental investigations were performed: solution binding affinities were determined through single-phase spectrophotometric titrations and the extent of conformational change upon binding was investigated with single-crystal X-ray crystallography. Both experimental methods compare the bicyclic malonamide (BMA), which is designed to be preorganized for binding trivalent lanthanides, to an analogous acyclic malonamide. Results from the spectrophotometric titrations indicate that BMA exhibits a 10-100x increase in binding affinity to Ln(III) over acyclic malonamide. In addition, BMA forms compounds with high ligand-metal ratios, even when competing with water and nitrate ligands for binding sites. The crystal structures exhibit no significant differences in the nature of the binding between Ln(III) and the BMA or acyclic malonamide. These results support the conclusion that rational ligand design can lead to compounds that enhance the binding affinities within a ligand class.
Chemistry Department, University of Oregon, Eugene, 97403-1253, USA.
Bevin W
BW
Parks
Robert D
RD
Gilbertson
James E
JE
Hutchison
Elisabeth Rather
ER
Healey
Timothy J R
TJ
Weakley
Brian M
BM
Rapko
Benjamin P
BP
Hay
Sergei I
SI
Sinkov
Grant A
GA
Broker
Robin D
RD
Rogers
D001643:Bridged Bicyclo Compounds / Q000737:chemistry*; D018360:Crystallography, X-Ray; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008024:Ligands; D008314:Malonates / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure
D001643:Bridged Bicyclo Compounds; D028581:Lanthanoid Series Elements; D008024:Ligands; D008314:Malonates; C008314:malonamide