title: Synthesis, Characterization, and Photophysical Studies of an Iron(III) Catecholate-Nitronylnitroxide Spin-Crossover Complex.
abstract: The synthesis and characterization of an Fe(III) catecholate-nitronylnitroxide (CAT-NN) complex (1-NN) that undergoes Fe(III) spin-crossover is described. Our aim is to determine whether the intraligand exchange coupling of the semiquinone-nitronylnitroxide Fe(II)(SQ-NN) excited state resulting from irradiation of the CAT → Fe(III) LMCT band would affect either the intrinsic photophysics or the iron spin-crossover event when compared to the complex lacking the nitronylnitroxide radical (1). X-ray crystallographic analysis provides bond lengths consistent with a ferric catecholate charge distribution. Mössbauer spectroscopy clearly demonstrates Fe(III) spin-crossover, hyperfine couplings, and a weak ferromagnetic Fe(III)-CAT-NN exchange, and spin-crossover is corroborated by variable-temperature magnetic susceptibility and electronic absorption studies. To explore the effect of the NN radical on photophysical processes, we conducted room-temperature transient absorption experiments. Upon excitation of the ligand-to-metal charge transfer band, an Fe(II)SQ state is populated and most likely undergoes fast intersystem crossing to the ligand field manifold, where it rapidly decays into a metastable low-spin Fe(III)CAT state, followed by repopulation of the high-spin Fe(III)CAT ground state. The decay components of 1-NN are slightly faster than those obtained for 1, perhaps due to the higher number of microstates present within the LMCT and LF manifolds for 1-NN. Although the effects of the NN radical are manifest in neither the spin-crossover nor the photophysics, our results lay the groundwork for future studies.
authors.affiliation: †Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Tichnell
authors.affiliation: †Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States.
authors.forename: David A
authors.initials: DA
authors.lastname: Shultz
authors.affiliation: ‡Department of Chemistry, Colgate University, 13 Oak Drive, Hamilton, New York 13346, United States.
authors.forename: Codrina V
authors.initials: CV
authors.lastname: Popescu
authors.affiliation: ⊥Department of Chemistry, Ursinus College, Collegeville, Pennsylvania 19426, United States.
authors.forename: Ivan
authors.initials: I
authors.lastname: Sokirniy
authors.affiliation: †Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Boyle