Charge-Transfer Phase Transition of a Cyanide-Bridged Fe(II) /Fe(III) Coordination Polymer.

Heterometallic Prussian blue analogues are known to exhibit thermally induced charge transfer, resulting in switching of optical and magnetic properties. However, charge-transfer phase transitions have not been reported for the simplest FeFe cyanide-bridged systems. A mixed-valence Fe(II) /Fe(III) cyanide-bridged coordination polymer, {[Fe(Tp)(CN)3 ]2 Fe(bpe)⋅5 H2 O}n , which demonstrates a thermally induced charge-transfer phase transition, is described. As a result of the charge transfer during this phase transition, the high-spin state of the whole system does not change to a low-spin state. This result is in contrast to FeCo cyanide-bridged systems that exhibit charge-transfer-induced spin transitions.

Molecular motor-driven abrupt anisotropic shape change in a single crystal of a Ni complex.

Many molecular machines with controllable molecular-scale motors have been developed. However, transmitting molecular movement to the macroscopic scale remains a formidable challenge. Here we report a single crystal of a Ni complex whose shape changes abruptly and reversibly in response to thermal changes at around room temperature. Variable-temperature single-crystal X-ray diffraction studies show that the crystalline shape change is induced by an unusual 90° rotation of uniaxially aligned oxalate molecules. The oxalate dianions behave as molecular-scale rotors, with their movement propagated through the entire crystalline material via intermolecular hydrogen bonding. Consequently, the subnanometre-scale changes in the oxalate molecules are instantly amplified to a micrometre-scale contraction or expansion of the crystal, accompanied by a thermal hysteresis loop. The shape change in the crystal was clearly detected under an optical microscope. The large directional deformation and prompt response suggest a role for this material in microscale or nanoscale thermal actuators.

Di-µ-tricyanido-tetra-cyanidobis[hydro-tris-(pyrazoylborato)]tetra-methanol-diiron(III)iron(II) di-methanol disolvate.

In the title complex, [Fe(II)Fe(III) 2(C9H10BN6)2(CN)6(CH3OH)4]·2CH3OH, two [Fe(III)(Tp)(CN)3](-) anions [Tp is hydro-tris-(pyrazoylborate)] are bridged by an [Fe(II)(MeOH)4](2+) cation, forming a centrosymmetric trinuclear unit. These units are connected via O-H⋯O and O-H⋯N hydrogen bonds involving the uncoordinated methanol solvent mol-ecules, forming a three-dimensional network.