Electronic interactions in verdazyl biradicals

A series of bisverdazyl biradicals in which the atoms bearing the greatest spin density are separated by several different aromatic spacer groups has been prepared in order to compare their properties to those of the nonspace d 1,1',5,5'-tetramethy1-6,6'-dioxo-3,3'-bisverdazyl (1). In addition, the 6 ,6'-dithio derivative (1,1',5,5'-tetramethyl-6,6'-dithio-3,3'-bis (7)) was prepared. Cyclic voltammograms of 1,4-bis(1,5-dimethyl-6-oxo-5-verdazyl)ben zene (5) and 2,5-bis(1,5-dimethyl-6-oxo-3-verdazyl)thiophene (6) both show a single two-electron oxidation near 700 mV. In contrast 1, 7, and 1,3-bis( 1,5-dimethyl-6-oxo-3-verdazyl)benzene (4) display two one-electron oxidatio n waves, with the first oxidative wave appearing also near 700 mV. The abso rption spectrum of each of these biradicals was red-shifted from the maximu m observed for 1. Biradicals 4, 5, and 6 exhibited linear Curie plots, alth ough a curved Curie plot was observed for 7 with J = 560 cm(-1).