Monomeric and dimeric copper(II) complexes of a novel tripodal peptide ligand: Structures stabilized via hydrogen bonding or ligand sharing

The novel tripodal ligand N-(bis(2-pyridyl)methyl)-2-pyridinecarboxamide (P y(3)AH) affords monomeric and dimeric copper(II) complexes with coordinated carboxamido nitrogens. Although many chloro-bridged dimeric copper(II) com plexes are known, [Cu(Py(3)A)(Cl)] (1) remains monomeric and planar with a pendant pyridine and does not form either a chloro-bridged dimer or the lig and-shared dimeric complex [Cu(Py(3)A)(Cl)](2) (4) in solvents such as CH3C N. When 1 is dissolved in alcohols, square pyramidal alcohol adducts [Cu(Py (3)A)(Cl)(CH3OH)] (2) and [Cu(Py(3)A)(Cl)(C2H5OH)] (3) are readily formed. In 2 and 3, the ROH molecules are bound at axial site of copper(II) and the weak axial binding of the ROH molecule is strengthened by intramolecular h ydrogen bonding between ROH and the pendant pyridine nitrogen. Two ligand-s hared dimeric species [Cu(Py(3)A)(Cl)](2) (4) and [Cu(PY(3)A)](2)(ClO4)(2) (5) have also been synthesized in which the pendant pyridine of one [Cu(Py( 3)A)] unit completes the coordination sphere of the other [Cu(Py(3)A)] neig hbor. These ligand-shared dimers are obtained in aqueous solutions or in co mplete absence of chloride in the reaction mixtures.