University Siegen, FB7 Solid State Physics, D-57068 Siegen, Germany.
J Am Chem Soc. 2009 Mar 4;131(8):2934-41. doi: 10.1021/ja808278s.
Self-assembly of Fe(2+) or Ni(2+) ions and the ditopic ligand 6,6',6''-bis(2-pyridyl)-2,2':4',4'':2'',2'''-quaterpyridine (btpy) through coordinative binding results in rodlike metallosupramolecular coordination polyelectrolytes (Fe-MEPE or Ni-MEPE). Sequential self-assembly with dihexadecyl phosphate (DHP) via electrostatic interactions between MEPE and DHP leads to the corresponding polyelectrolyte amphiphile complex (PAC) with liquid crystalline properties. The MEPE rods are embedded in between the interdigitated DHP layers. Upon heating above room temperature, the Fe-PAC shows an irreversible spin-crossover (SCO) from a diamagnetic low-spin (LS) to a paramagnetic high-spin (HS) state accompanied by a color change from dark blue to pale blue. The SCO is nearly complete (95%) and directly associated with the structure changes induced by the melting of the amphiphilic matrix. The original Fe-PAC architecture does not reassemble upon cooling and remains in a disordered frozen HS state. However, dissolving the heated PAC induces reassembly, and the original dark blue, diamagnetic, ordered material is completely recovered. In comparison to Fe-PAC, Ni-PAC shows the same lamellar structure and the same temperature depended structure changes but has a constant magnetic moment. In contrast to Fe-PAC, in neat Fe-MEPE the SCO depends on the history of the sample and in particular on the amount of included solvent as thermogravimetric analysis, differential scanning calorimetry (DSC), and magnetic measurements indicate. Solid MEPE does not have liquid crystalline properties, and, therefore, the induced structure changes upon heating are constrained by the solid-state architecture, and thus, the SCO in Fe-MEPE is incomplete.
Fe(2+) 或 Ni(2+) 离子与双齿配体 6,6',6''-双(2-吡啶基)-2,2':4',4'':2'',2'''-四吡啶(btpy) 通过配位键自组装形成棒状金属超分子配位聚合物(Fe-MEPE 或 Ni-MEPE)。通过 MEPE 和 DHP 之间的静电相互作用进行顺序自组装，导致具有液晶性质的相应聚合物两亲复合物(PAC)。MEPE 棒嵌入交错的 DHP 层之间。在室温以上加热时，Fe-PAC 发生不可逆的自旋交叉(从顺磁低自旋(LS)到铁磁高自旋(HS))，同时颜色从深蓝色变为浅蓝色。SCO 几乎完全(95%)，并直接与由两亲基质熔融引起的结构变化相关。原始的 Fe-PAC 结构在冷却时不会重新组装，并保持无序的冻结 HS 状态。然而，加热的 PAC 的溶解会诱导重新组装，并且原始的深蓝色、抗磁性、有序材料完全恢复。与 Fe-PAC 相比，Ni-PAC 具有相同的层状结构和相同的温度依赖性结构变化，但具有恒定的磁矩。与 Fe-PAC 不同，在纯 Fe-MEPE 中，SCO 取决于样品的历史，特别是取决于包含的溶剂的量，热重分析、差示扫描量热法(DSC)和磁测量表明。固态 MEPE 没有液晶性质，因此，加热时诱导的结构变化受到固态结构的限制，因此 Fe-MEPE 中的 SCO 是不完全的。
