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...

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Bibliographic Details
Published in:Inorganic chemistry 2006-02, Vol.45 (4), p.1498-1507
Main Authors: Parks, Bevin W, Gilbertson, Robert D, Hutchison, James E, Healey, Elisabeth Rather, Weakley, Timothy J. R, Rapko, Brian M, Hay, Benjamin P, Sinkov, Sergei I, Broker, Grant A, Rogers, Robin D
Format: Article
Language:English
Subjects:
AFFINITY
bicyclic
Bridged Bicyclo Compounds - chemistry
CHEMISTRY
CONFORMATIONAL CHANGES
CRYSTAL STRUCTURE
CRYSTALLOGRAPHY
Crystallography, X-Ray
DESIGN
Lanthanoid Series Elements - chemistry
Ligands
malonamides
Malonates - chemistry
MATERIALS SCIENCE
Models, Molecular
Molecular Structure
NITRATES
RARE EARTHS
WATER
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Summary: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 10−100× 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.
ISSN:0020-1669
1520-510X
DOI:10.1021/ic050437d