Spin Delocalization in the Copper(I) Complexes of Bis(verdazyl) Diradicals

1,1‘,5,5‘-tetramethyl-6,6‘-dioxobis(verdazyl) (BVD) reacts with copper(I) halides in acetonitrile and copper(II) halides in methanol to give copper(I) coordination polymers of composition [Cu 2 X 2 (BVD)] x . When X = Cl and X = Br, these polymers crystallize in orthorhombic unit cells with dimensions a = 6.684(1) Å, b = 12.524(3) Å, and c = 8.717(2) Å (X = Cl) and a = 12.680(2) Å, b = 6.744(1) Å, and c = 8.822(2) Å (X = Br). With X = I, powder diffraction indicates a monoclinic unit cell with dimensions a = 12.669 Å, b = 8.461 Å, c = 7.679 Å, and β = 91.88°, although poor crystal quality prevented a full structure determination. Magnetic susceptibility measurements taken on the three polymers indicate that the spins couple in one-dimensional chains with alternating exchange parameters: J 1 = −190 cm - 1, J 2 = −116 cm - 1 (X = Cl); J 1 = −200 cm - 1, J 2 = −110 cm - 1 (X = Br); and J 1 = −271 cm - 1, J 2 = −200 cm - 1 (X = I). Variable temperature ESR measurements on the unstable monomeric complex resulting from reaction of BVD with (CH 3 O) 3 PCuI indicate an interradical exchange parameter J of −230 cm - 1 . ESR spectra of all three complexes show extremely broad, featureless lines as a result of very rapid spin−lattice relaxation. The reduction in exchange between the two halves of the bis(verdazyl) ligand upon coordination, and the unusual ESR properties, require a delocalized structure, with significant spin density on the copper atom. Variation of the auxiliary ligands on the copper atom allows tuning of the intramolecular exchange.