title: Structural and magnetic evidence concerning spin crossover in formamidinate compounds with ru2 5+ cores.
abstract: The magnetic and structural properties of two Ru2(DArF)4Cl compounds, where DArF is the anion of a diaryl formamidine, are presented here. The compounds with Ar = p-anisyl and m-anisyl both show temperature dependence of chiT (chi = molar magnetic susceptibility), but for different reasons. For the para compound, there is a Boltzmann distribution between a pi*3 ground state and a delta*pi*2 upper state, and this is confirmed by a temperature dependence of the Ru-Ru bond length: 2.4471(5) A at 23 K and 2.3968(5) A at 300 K. For the meta compound, a delta*pi*2 configuration persists over the range of 23-300 K as shown by an invariant Ru-Ru bond length, but the chiT drops with decreasing temperature owing to zero-field splitting of a 4B2u ground state.
authors.affiliation: Department of Chemistry and Laboratory for Molecular Structure and Bonding, P.O. Box 30012, Texas A&M University, College Station, Texas 77842-3012, USA.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Angaridis
authors.forename: F Albert
authors.initials: FA
authors.lastname: Cotton
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Murillo
authors.forename: Dino
authors.initials: D
authors.lastname: Villagrán
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Wang