Magnetic properties and crystal structures of 1,5-diphenylverdazyls with electron acceptor groups in the 3-position

The magnetic properties of four diphenylverdazyls (2-5) with electron acceptor groups in the 3-position were studied by measuring the magnetic susceptibility and heat capacity. The crystal structures of 3 and 4 were determined, and for 2 the crystal structure analysis led to an improved refinement. Verdazyl 2 was found to be an antiferromagnet with a Neel temperature of T-N = 1.16 +/- 0.04 K. Above the transition temperature T-N, 2 behaves as a quasi-one-dimensional Heisenberg ferromagnet with the intrachain exchange interaction of 2J/k(B) = +7.0 +/- 1.0 K. The interchain exchange interaction zJ'/k(B) was estimated to be -1.5 +/- 0.2 K, where z is the number of interchain bonds per spin. On the other hand, 3 and 5 behave as 1D nonalternating and alternating Heisenberg antiferromagnets with an exchange interaction of 2J/k(B) = -11.6 K and 2J(1)/k(B) = -113 K (alternation parameter alpha = J(2)/J(1) = 0.4), respectively. The susceptibility of 4 follows the Curie-Weiss law with a negative Weiss constant of -18 K above 100 K. Below 100 K, 4 showed anomalous magnetic behavior that cannot be explained by a simple model. The magnetic properties of 2-4 are discussed based on the results obtained by crystal structure analyses.