Kawabata Shintaro, Chorazy Szymon, Zakrzewski Jakub J, Imoto Kenta, Fujimoto Takashi, Nakabayashi Koji, Stanek Jan, Sieklucka Barbara, Ohkoshi Shin-Ichi
Department of Chemistry, School of Science , The University of Tokyo , 7-3-1 Hongo , Bunkyo-ku, Tokyo 113-0033 , Japan.
Faculty of Chemistry , Jagiellonian University , Gronostajowa 2 , 30-387 Krakow , Poland.
Inorg Chem. 2019 May 6;58(9):6052-6063. doi: 10.1021/acs.inorgchem.9b00361. Epub 2019 Apr 19.
We report a unique synthetic route toward the multistep spin crossover (SCO) effect induced by utilizing the partial ligand transformation during the crystallization process, which leads to the incorporation of three different Fe complexes into a single coordination framework. The 3-acetoxypyridine (3-OAcpy) molecules were introduced to the self-assembled Fe-[M(CN)] (M = Mo, Nb) system in the aqueous solution which results in the partial hydrolysis of the ligand into 3-hydroxypyridine (3-OHpy). It gives two novel isostructural three-dimensional {Fe(3-OAcpy)(3-OHpy)[M(CN)]}· nHO (M = Mo, n = 0, FeMo; M = Nb, n = 1, FeNb) coordination frameworks. They exhibit an unprecedented cyanido-bridged skeleton composed of {FeM} coordination nanotubes bonded by additional Fe complexes. These frameworks contain three types of Fe sites differing in the attached organic ligands, [Fe1(3-OAcpy)(μ-NC)], [Fe2(3-OHpy)(μ-NC)], and [Fe3(3-OAcpy)(3-OHpy)(μ-NC)], which lead to the thermal two-step Fe SCO, as proven by X-ray diffraction, magnetic susceptibility, UV-vis-NIR optical absorption, and Fe Mössbauer spectroscopy studies. The first step of SCO, going from room temperature to the 150-170 K range with transition temperatures of 245(5) and 283(5) K for FeMo and FeNb, respectively, is related to Fe1 sites, while the second step, occurring at the 50-140 K range with transition temperatures of 70(5) and 80(5) K for FeMo and FeNb, respectively, is related to Fe2 sites. The Fe3 site with both 3-OAcpy and 3-OHpy ligands does not undergo the SCO at all. The observed two-step SCO phenomenon is explained by the differences in the ligand field strength of the Fe complexes and the role of their alignment in the coordination framework. The simultaneous application of two related pyridine derivatives is the efficient synthetic route for the multistep Fe SCO in the cyanido-bridged framework which is a promising step toward rational design of advanced spin transition molecular switches.
我们报道了一种独特的合成路线，通过在结晶过程中利用部分配体转化诱导多步自旋交叉（SCO）效应，这导致三种不同的铁配合物纳入单一配位框架。将3-乙酰氧基吡啶（3-OAcpy）分子引入水溶液中的自组装铁-[M(CN)]（M = Mo，Nb）体系，导致配体部分水解为3-羟基吡啶（3-OHpy）。这产生了两种新颖的同构三维{Fe(3-OAcpy)(3-OHpy)[M(CN)]}·nH₂O（M = Mo，n = 0，FeMo；M = Nb，n = 1，FeNb）配位框架。它们展现出由{FeM}配位纳米管通过额外的铁配合物键合而成的前所未有的氰基桥连骨架。这些框架包含三种在连接的有机配体上不同的铁位点，[Fe1(3-OAcpy)(μ-NC)]、[Fe2(3-OHpy)(μ-NC)]和[Fe3(3-OAcpy)(3-OHpy)(μ-NC)]，经X射线衍射、磁化率、紫外-可见-近红外光吸收和铁穆斯堡尔谱研究证明，这导致了热两步铁SCO。SCO的第一步，从室温到150 - 170 K范围，FeMo和FeNb的转变温度分别为245(5) K和283(5) K，与Fe1位点相关，而第二步，发生在50 - 140 K范围，FeMo和FeNb的转变温度分别为70(5) K和80(5) K，与Fe2位点相关。具有3-OAcpy和3-OHpy两种配体的Fe3位点根本不发生SCO。观察到的两步SCO现象通过铁配合物配体场强度的差异及其在配位框架中的排列作用来解释。同时应用两种相关的吡啶衍生物是氰基桥连框架中多步铁SCO的有效合成路线，这是迈向合理设计先进自旋转变分子开关的有希望的一步。
