M. Mito et al., MAGNETIC-PROPERTIES AND CRYSTAL-STRUCTURES OF 1,5-DIPHENYLVERDAZYLS WITH ELECTRON-ACCEPTOR GROUPS IN THE 3-POSITION, JOURNAL OF PHYSICAL CHEMISTRY B, 101(46), 1997, pp. 9517-9524
The magnetic properties of four diphenylverdazyls (2-5) with electron
acceptor groups in the 3-position were studied by measuring the magnet
ic susceptibility and heat capacity. The crystal structures of 3 and 4
were determined, and for 2 the crystal structure analysis led to an i
mproved refinement. Verdazyl 2 was found to be an antiferromagnet with
a Neel temperature of T-N = 1.16 +/- 0.04 K. Above the transition tem
perature T-N, 2 behaves as a quasi-one-dimensional Heisenberg ferromag
net 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 He
isenberg antiferromagnets with an exchange interaction of 2J/k(B) = -1
1.6 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 si
mple model. The magnetic properties of 2-4 are discussed based on the
results obtained by crystal structure analyses.