title: Anion dependence in the spin-crossover properties of a Fe(II) podand complex.
abstract: We report the syntheses, characterisations, and spin state behaviours of salts of the tripodal-ligated Fe(II) complex [FeL(6-OH)]X(2) (L(6-OH) = tris{4-[(6-methanol)-2-pyridyl]-3-aza-3-butenyl}amine, X = OTf(-) (1), Br(-) (2), I(-) (3), BPh(4)(-) (4)). Covalent linking of the ligand arms is imperative as a high-spin bis(tridentate) complex (5) is formed when a non-tethered ethyl iminopyridine ligand (L(2) = 4-[(6-methanol)-2-pyridyl]-3-aza-3-butenyl) is used. For salts 1-4, thermally-induced spin-crossover (SCO) is observed in the solid state, with dependence on anion and solvate molecules. Salts with larger anions show more complete SCO centred at higher temperatures (1 > 3 > 2); the triflate salt 1 (T(1/2) = 173 K) also shows the strongest cooperativity of the compounds examined. Hydrogen bonding appears to be critical to SCO in this family of salts: limiting interactions by use of tetraphenylborate produces a high-spin complex down to 5 K. In protic solvents such as methanol, spectra of [FeL(6-OH)](2+) are largely unchanged over a period of three days, but dissociate when interrogated with strong field bidentate ligands. Compounds 1-3, and 5 remain high spin in solution down to 180 K, consistent with the data obtained in the solid state.
authors.affiliation: Department of Chemistry, Colorado State University, Fort Collins, CO 80523-1872, USA.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Klug
authors.forename: Ashley M
authors.initials: AM
authors.lastname: McDaniel
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Fiedler
authors.forename: Kelsey A
authors.initials: KA
authors.lastname: Schulte
authors.forename: Brian S
authors.initials: BS
authors.lastname: Newell
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Shores