Further structural and magnetic studies of tricopper dipyridylamido complexes

The compound Cu-3(dpa)(4)Cl-2, 1 (dpa = the anion of dipyridylamine), which was first synthesized and characterized in 1990, has been structurally characterized in three new crystal forms having Cu...Cu separations of 2.47-2.49 Angstrom. Its magnetic properties have been studied fully. Reaction of Cu-3(dpa)(4)Cl-2 with 2 equiv of silver tetrafluoroborate yields Cu-3(dpa)(4)(BF4)(2) (2), a compound with a similar linear trinuclear structure but coordinated BF4 anions in each axial position and having shorter Cu...Cu distances of 2.40 Angstrom but similar magnetic properties. Least squares fitting of the magnetic susceptibility data for I and 2 gave isotropic g values of 2.007 and 2.130 and exchange parameters of -373 and -411 cm(-1), respectively. This suggests the possible existence of an exchange pathway in which the metal atoms interact directly with each other.