title: Substituent effects on exchange coupling: 5-Aryl-substituted semiquinones and their complexes with MnII and CuII.
abstract: A series of functionalized radical anion semiquinone (SQ-Ar) ligands and their MnII- and CuIIhydro-tris(3-cumenyl-5-methylpyrazolyl)borate (TpCum,MeMII) complexes were prepared and characterized. The semiquinone ligands have substituted phenyl rings (Ar = -C6H5NO2, -C6H5OMe, -C6H5-tert-Bu, etc.) attached to the SQ 5-position. Despite the "remoteness" of the phenyl ring substituents, the MII-SQ exchange parameters, J, were found to vary nearly 3-fold. Attempts to quantify the substituent effects on J are complicated by the fact that not all complexes could be structurally characterized. As such, substituent effects and phenyl-ring torsion angles could conspire to produce the observed variation in J values. Although there is no clear trend in the J values as a function of SQ substituent for the MnII complexes, for the CuII complexes, electron-withdrawing substituents on the phenyl ring have greater ferromagnetic J values than the CuII complexes of SQ ligands with electron-donating substituents. This trend suggests a FM contribution from MLCT excited states in the copper complexes.
authors.affiliation: Department of Chemistry, North Carolina State University, P.O. Box 8204, Raleigh, North Carolina 27695, USA. David_Shultz@ncsu.edu
authors.forename: David A
authors.initials: DA
authors.lastname: Shultz
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Sloop
authors.forename: Tashni-Ann
authors.initials: TA
authors.lastname: Coote
authors.forename: Mithra
authors.initials: M
authors.lastname: Beikmohammadi
authors.forename: Jeff
authors.initials: J
authors.lastname: Kampf
authors.forename: Paul D
authors.initials: PD
authors.lastname: Boyle