title: Thermochromic and photoresponsive cyanometalate Fe/Co squares: toward control of the electron transfer temperature.
abstract: Two structurally related and photoresponsive cyanide-bridged Fe/Co square complexes, {Fe2Co2}, are reported: {[(Tp(Me))Fe(CN)3]2[Co(bpy)2]2[(Tp(Me))Fe(CN)3]2}·12H2O (2) and {[(Tp(Me))Fe(CN)3]2[Co(bpy)2]2[BPh4]2}·6MeCN (3), where Tp(Me) and bpy are hydridotris(3-methylpyrazol-1-yl)borate and 2,2'-bipyridine, respectively. Through electrochemical and spectroscopic studies, the Tp(Me) ligand appears to be a moderate σ donor in comparison to others in the [NEt4][(Tp(R))Fe(III)(CN)3] series [where Tp(R) = Tp, hydridotris(pyrazol-1-yl)borate; Tp(Me) = hydridotris(3-methylpyrazol-1-yl)borate; pzTp = tetrakis(pyrazol-1-yl)borate; Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate; Tp*(Me) = hydridotris(3,4,5-trimethylpyrazol-1-yl)borate]. The spectroscopic, structural, and magnetic data of the {Fe2Co2} squares indicate that thermally-induced intramolecular electron transfer reversibly converts {Fe(II)LS(μ-CN)Co(III)LS} pairs into {Fe(III)LS(μ-CN)Co(II)HS} units near ca. 230 and 244 K (T1/2) for 2 and 3, respectively (LS: low spin; HS: high spin). These experimental results show that 2 and 3 display light-induced {Fe(III)LS(μ-CN)Co(II)HS} metastable states that relax to thermodynamic {Fe(II)LS(μ-CN)Co(III)LS} ones at ca. 90 K. Ancillary Tp(R) ligand donor strength appears to be the dominant factor for tuning electron transfer properties in these {Fe2Co2} complexes.
authors.affiliation: Department of Chemistry and Biochemistry and ⊥Center for Nanoscience, University of Missouri-St. Louis , St. Louis, Missouri 63121, United States.
authors.forename: Yuan-Zhu
authors.initials: YZ
authors.lastname: Zhang
authors.forename: Philip
authors.initials: P
authors.lastname: Ferko
authors.forename: Diana
authors.initials: D
authors.lastname: Siretanu
authors.forename: Rodica
authors.initials: R
authors.lastname: Ababei
authors.forename: Nigam P
authors.initials: NP
authors.lastname: Rath
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Shaw
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Clérac
authors.forename: Corine
authors.initials: C
authors.lastname: Mathonière
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Holmes