Molecular Structures and Magnetochemistry of Two (β-Oxooctaethylchlorinato)copper(II) Derivatives: [Cu(oxoOEC)] and [Cu(oxoOEC^•)]SbCl₆

The preparation and characterization of the β-oxochlorin derivative [3,3,7,8,12,13,17,18-octaethyl-(3H)-porphin-2-onato(2−)]copper(II), [Cu(oxoOEC)], and its π-cation radical derivative, [Cu(oxoOEC•)][SbCl6], are described. Both compounds have been characterized by single-crystal X-ray structure determinations; IR, UV/vis/near-IR, and EPR spectroscopies; and temperature-dependent magnetic susceptibility measurements. Crystals of [Cu(oxoOEC)] have two crystallographically distinct molecules, one at a general position ([Cu(oxoOEC)]-gen) and a second at a special position ([Cu(oxoOEC)]-spe). [Cu(oxoOEC)]-gen has a S4-saddled conformation whereas [Cu(oxoOEC)]-spe has a modest ruffled conformation. [Cu(oxoOEC•)][SbCl6] shows a cofacial dimeric unit in the solid state, with a mean plane separation of 3.41 Å and a lateral shift of 5.47 Å. Crystal data for [Cu(oxoOEC)]: monoclinic, space group C2/c, Z = 12, a = 38.404(8) Å, b = 14.692(6) Å, c = 16.977(11) Å, β = 101.46(2)°. Crystal data for [Cu(oxoOEC•)][SbCl6]: triclinic, space group P1̄, Z = 2, a = 13.063(1) Å, b = 14.108(2) Å, c = 11.486(2) Å, α = 93.77(3)°, β = 102.17(1)°, γ = 74.07(1)°. The EPR spectrum of [Cu(oxoOEC•)][SbCl6] in frozen dichloromethane at 77 K shows the characteristics of a dimeric copper(II) triplet state. Two broad, concentration-dependent near-IR “dimer bands” appear at 1285 and 1548 nm for [Cu(oxoOEC•)][SbCl6]. Solid-state magnetic susceptibility measurements for [Cu(oxoOEC•)][SbCl6] resulted in a large temperature dependence of the magnetic moments that can best be fit with a four-spin model. This model includes antiferromagnetic intermolecular copper−copper coupling (2JCu-Cu = −70 cm-1), antiferromagnetic radical−radical coupling (2Jr-r = −139 cm-1), and ferromagnetic intramolecular copper−radical coupling (2JCu-r = 139 cm-1).