Intramolecular Hydrogen Bonding in Cu^II Complexes with 2,6-Pyridinedicarboxamide Ligands: Synthesis, Structural Characterization, and Physical Properties

Authors

Denan Wang, Marquette University
Sergey V. Lindeman, Marquette UniversityFollow
Adam T. Fiedler, Marquette UniversityFollow

Document Type

Article

Language

eng

Publication Date

9-2013

Publisher

Wiley

Source Publication

European Journal of Inorganic Chemistry

Source ISSN

1434-1948

Abstract

The significance of second-sphere interactions in synthetic catalysts and metalloenzyme active sites has encouraged the development of ligand frameworks capable of supporting intramolecular hydrogen-bonding networks. With this approach in mind, we prepared a series of 2,6-pyridinedicarboxamide ligands (H₂L^X) that feature outer-sphere heterocyclic groups (pyridine, pyrimidine, or quinoline rings). Reaction with CuCl₂ yields complexes with the general formula [CuCl₂(L^X{H}₂)] (1^X), in which the pincer ligands coordinate to the Cu^II center in a tridentate fashion through the central pyridine and two amidato nitrogen atoms. The L^X{H}₂ ligands have no net charge, however, as the pendant heterocycles are both protonated. X-ray crystallographic studies revealed that the two outer-sphere N–H groups form intramolecular hydrogen bonds with the chlorido ligands. Modification of the syntheses provided Cu^II complexes (i.e., 2^X, 3^X) that contain an aqua ligand hydrogen bonded to the outer-sphere group(s). Whereas complexes with the L^X{H}₂ ligands are mononuclear, deprotonation gives rise to dimeric complexes (i.e., 4^X, 5^X) in which one of the pendant heterocycles coordinates to a second Cu^II center. The complexes were also examined with electronic absorption spectroscopy, cyclic voltammetry, and density functional theory. Our results indicate that the L^X{H}₂ ligands, despite their neutrality, maintain the strong σ-donating ability of anionic pyridine-amidato ligands.

Comments

Accepted version. European Journal of Inorganic Chemistry, Vol. 2013 (September 2013): 4473-4484. DOI. © 2013 Wiley VCH-Verlag. Used with permission.

Recommended Citation

Wang, Denan; Lindeman, Sergey V.; and Fiedler, Adam T., "Intramolecular Hydrogen Bonding in Cu^II Complexes with 2,6-Pyridinedicarboxamide Ligands: Synthesis, Structural Characterization, and Physical Properties" (2013). Chemistry Faculty Research and Publications. 575.
https://epublications.marquette.edu/chem_fac/575