Spin crossover and reversible single-crystal to single-crystal transformation behaviour in two cyanide-bridged mixed-valence {(Fe2Fe2II)-Fe-III} clusters

摘要

The reactions of tricyanometallate precursors, (Ph3PMe)[(Tp(4-Me)) Fe(CN)(3)center dot 0.5CH(3)CN] (1) (Tp(4-Me) = tri(4-methyl- pyrazol-1-yl)borate) and (NBu4)[((Me)Tp) Fe(CN)(3)] ((Me)Tp = methyltris(pyrazolyl) borate) with the presence of the tetradentate tpa ligand (tpa = tris(2-pyridylmethyl) amine) and Fe(ClO4)(2)center dot 6H(2)O afford two new cyano-bridged mixed-valence {Fe-2(III) Fe-2(II)} molecular squares: [(Tp(4-Me)) Fe-III(CN)(3)](2)[Fe-II(tpa)](2)center dot 2ClO(4)center dot H2O (2 center dot H2O) and [((Me)Tp) Fe-III(CN)(3)](2)[Fe-II(tpa)](2)center dot 2ClO(4)center dot CH3OH (3 center dot CH3OH). Solvent-exchange compounds of 3 center dot CH3OH, [((Me)Tp) Fe-III(CN)(3)](2)[Fe-II(tpa)](2)center dot 2ClO(4)center dot 2H(2)O (3 center dot 2H(2)O), 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 FeII centres and magnetic susceptibility measurements. All compounds exhibit SCO behaviour near room temperature (T-1/2 = 320 K for 2 center dot H2O; 302 K for 2; 292 K for 3 center dot CH3OH; 306 K for 3 center dot 2H(2)O 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 {Fe-4(mu-CN)(4)} core and deviations of bent Delta Fe-N C angles play a key role in tuning the transition temperature of these similar mixedvalence {Fe-2(III) Fe-2(II)} complexes.