Reaction of a macrocyclic ligand precursor comprising two bis(carboxamido)pyridine units (H4L4) connected by ethylene linkers with NMe4OH and CuX2 (X = Cl, OAc, or OTf) yielded monocopper complexes [NMe4][(H2L4)Cu(X)] (X = Cl (3), OAc (4), or OH (5)), in contrast to previous work using a related ligand with ortho-phenylene linkers wherein dicopper compounds were isolated. X-ray structures of the complexes revealed hydrogen bonding from the free carboxamide N-H groups in the doubly protonated form of the ligand (H2L4(-) ) to the monodentate fourth ligand coordinated to the Cu(II) ion. Similar secondary sphere hydrogen bonding interactions were identified in multinuclear compounds [NMe4]2[((H2L4)Cu)n(CO3)] (n = 2 or 3) that were isolated from exposure of 5 to air. Cyclic voltammetry revealed oxidations of 3 and 5 at potentials ~300 mV higher than analogous monocopper complexes of bis(arylcarboxamido)pyridine ligands which lack the intramolecular hydrogen bonds, consistent with removal of electron density from the metal center by the hydrogen bonding array. Another ligand variant (H4L5) with ortho-phenylene linkers and only one bis(carboxamido)pyridine moiety yielded monocopper complexes [NMe4][(H2L5)Cu(OAc)] • DMF (8) and [NMe4][(H2L5)CuCl)] • CH3CN (9), but the X-ray structures revealed a different hydrogen bonding arrangement to the solvate molecules. Nonetheless, a high redox potential for 9 was observed, consistent with intramolecular hydrogen bonding interactions in solution.
This research output has an Altmetric Attention Score of 2. This is our high-level measure of the quality and quantity of online attention that it has received. This Attention Score, as well as the ranking and number of research outputs shown below, was calculated when the research output was last mentioned on 23 November 2015.
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