Polynuclear Cu₄L₄ Copper(II) Aminyl Radical Coordination Complexes

Abstract

We describe the structural features and magnetic properties of two polynuclear copper(II) complexes containing a redox-active ligand. These neutral complexes each bear the formula RLCu (R = Bu, Me) with the ligand in a dianion-aminyl radical oxidation state. X-ray data and density functional theory calculations support an aminyl-type radical character in these complexes, making these the first polynuclear metal aminyl radical complexes.

A Neutral Fe4tBuL4 All Ferric Grid Complex: Structural and Variable Temperature Magnetic Properties

“…This structural data suggests a dominant Fe 3+ oxidation state assignment for the metal in 1 . This result stands in contrast to an earlier reported Cu 2+ complex of the same ligand, in which a neutral M 4 t Bu L 4 structure was also produced; however, each of the four ligands was identified to be in a dianion‐aminyl radical oxidation state with unusual structural parameters not observed in 1 . These include very long bonds between the central ring and one of the quinoline rings, which is also rotated nearly perpendicular to the rest of the ligand in the complex.…”

“…In contrast to the electrochemical properties of other reported [2×2] grid complexes, the lower potential anodic processes can be assigned to ligand‐centered oxidation events (the redox properties of t Bu H 3 L were described previously and feature a low positive potential anodic wave). The electron‐rich t Bu L 3– trianion is easily oxidized; in the Cu 4 t Bu L 4 complex reported earlier, the ligand was oxidized in a glove box upon coordination to Cu(ClO 4 ) 2 · 6H 2 O to an aminyl radical dianion, with the spin density localized on one exocyclic N atom. However, the Cu 4 t Bu L 4 complex was very unstable in solution.…”

“…The bond ( Figure 3 tBu L 4 structure was also produced; however, each of the four ligands was identified to be in a dianion-aminyl radical oxidation state with unusual structural parameters not observed in 1. [21] These include very long bonds between the central ring and one of the quinoline rings, which is also rotated nearly perpendicular to the rest of the ligand in the complex. A very large spin density was calculated on the exocyclic N atom attached to this quinoline ring in Cu 4 tBu L 4 .…”

“…General procedures: All reagents were commercially available and used as received unless otherwise stated. Ligand t Bu H 3 L was prepared according to the reported method , . Anhydrous solvents (MeOH, THF & CH 2 Cl 2 ) were obtained by distillation over CaH 2 or obtained from a PureSolve solvent purification system.…”

“…Ligand tBu H 3 L was prepared according to the reported method. [16,21] Anhydrous solvents (MeOH, THF & CH 2 Cl 2 ) were obtained by distillation over CaH 2 or obtained from a PureSolve solvent purification system. FT-IR spectra were recorded with a Shimadzu IRAffinity spectrometer as KBr discs.…”