title: Spin crossover and reversible single-crystal to single-crystal transformation behaviour in two cyanide-bridged mixed-valence {FeFe} clusters.
abstract: The reactions of tricyanometallate precursors, (Ph3PMe)[(Tp4-Me)Fe(CN)3·0.5CH3CN] (1) (Tp4-Me= tri(4-methyl-pyrazol-1-yl)borate) and (NBu4)[(MeTp)Fe(CN)3] (MeTp = methyltris(pyrazolyl)borate) with the presence of the tetradentate tpa ligand (tpa = tris(2-pyridylmethyl)amine) and Fe(ClO4)2·6H2O afford two new cyano-bridged mixed-valence {FeFe} molecular squares: [(Tp4-Me)FeIII(CN)3]2[FeII(tpa)]2·2ClO4·H2O (2·H2O) and [(MeTp)FeIII(CN)3]2[FeII(tpa)]2·2ClO4·CH3OH (3·CH3OH). Solvent-exchange compounds of 3·CH3OH, [(MeTp)FeIII(CN)3]2[FeII(tpa)]2·2ClO4·2H2O (3·2H2O), and their solvent-free form (2 and 3) are also obtained, respectively. The spin crossover (SCO) properties of all compounds are confirmed by detailed structural analyses of the coordination environments of the FeIIcentres and magnetic susceptibility measurements. All compounds exhibit SCO behaviour near room temperature (T1/2= 320 K for 2·H2O; 302 K for 2; 292 K for 3·CH3OH; 306 K for 3·2H2O and 290 K for 3) and reversible single-crystal to single-crystal (SC-SC) transformations induced by guest desorption and resorption or solvent exchange. The transition temperature close to room temperature can be tuned by the dehydration and re-hydration processes. The structure-property analysis discloses that the distorted {Fe4(μ-CN)4} core and deviations of bent ∠Fe-N[triple bond, length as m-dash]C angles play a key role in tuning the transition temperature of these similar mixed-valence {FeFe} complexes.
authors.affiliation: College of Chemistry, Key Laboratory of Pesticide and Chemical Biology of Ministry of Education, Central China Normal University, 430079 Wuhan, P. R. China. dfli@mail.ccnu.edu.cn and Hubei Collaborative Innovation Center for Rare Metal Chemistry, Hubei Key Laboratory of Pollutant Analysis and Reuse Technology, Institute for Advanced Materials, Hubei Normal University, 435002 Huangshi, P. R. China.
authors.forename: Chunyang
authors.initials: C
authors.lastname: Zheng
authors.affiliation: College of Chemistry, Key Laboratory of Pesticide and Chemical Biology of Ministry of Education, Central China Normal University, 430079 Wuhan, P. R. China. dfli@mail.ccnu.edu.cn.
authors.forename: Juping
authors.initials: J
authors.lastname: Xu
authors.affiliation: College of Chemistry and Materials Science, Hubei Engineering University, 432000 Xiaogan, P. R. China.
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, 361005 Xiamen, P. R. China.
authors.forename: Jun
authors.initials: J
authors.lastname: Tao
authors.affiliation: College of Chemistry, Key Laboratory of Pesticide and Chemical Biology of Ministry of Education, Central China Normal University, 430079 Wuhan, P. R. China. dfli@mail.ccnu.edu.cn and State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, 361005 Xiamen, P. R. China.
authors.forename: Dongfeng
authors.initials: D
authors.lastname: Li