Hexaethyltripyrrindione (H₃Et₆tpd): A Non‐Innocent Ligand Forming Stable Radical Complexes with Divalent Transition‐Metal Ions

Abstract

Nickel, palladium, and copper complexes of the tripyrrolic ligand hexaethyltripyrrindione (H 3 Et 6 tpd, 1 ) have been prepared and characterized by UV/Vis and EPR spectroscopy, as well as by single‐crystal X‐ray structure determination. In all cases the metal ion is coordinated in a distorted square‐planar geometry carrying a water ligand at the fourth coordination site. The Et 6 tpd ligand acts as a radical dianion in all cases. In solution, monomeric species are present in which the open‐shell character of the ligand becomes apparent through EPR spectroscopic measurements. In the solid state, the compounds form polymorphs with tightly bonded π–π dimers and chains showing small interplanar distances of 3.191–3.493 Å to one or more neighboring molecules. Magnetic measurements on the complexes confirmed the radical character of the tripyrrindione ligand and revealed strong intermolecular magnetic interactions in these complexes.