Iasco Olga, Rivière Eric, Guillot Régis, Buron-Le Cointe Marylise, Meunier Jean-François, Bousseksou Azzedine, Boillot Marie-Laure
ICMMO-ECI, UMR CNRS 8182, Université Paris-Sud , 91405 Orsay cedex, France.
Inorg Chem. 2015 Feb 16;54(4):1791-9. doi: 10.1021/ic5027043. Epub 2015 Jan 15.
We focus here on the properties of Fe complexes formed with Schiff bases involved in the chemistry of Fe(III) spin-transition archetypes. The neutral Fe(pap-5NO2)2 (1) and Fe(qsal-5NO2)2·Solv (2 and 2·Solv) compounds (Solv = 2H2O) derive from the reaction of Fe(II) salts with the condensation products of pyridine-2-carbaldehyde with 2-hydroxy-5-nitroaniline (Hpap-5NO2) or 5-nitrosalicylaldehyde with quinolin-8-amine (Hqsal-5NO2), respectively. While the Fe(qsal-5NO2)2·Solv solid is essentially low spin (S = 0) and requires temperatures above 300 K to undergo a S = 0 ↔ S = 2 spin-state switching, the Fe(pap-5NO2)2 one presents a strongly cooperative first-order transition (T↓ = 291 K, T↑ = 308 K) centered at room temperature associated with a photomagnetic effect at 10 K (TLIESST = 58 K). The investigation of these magnetic behaviors was conducted with single-crystal X-ray diffraction (1, 100 and 320 K; 2, 100 K), Mössbauer, IR, UV-vis (1 and 2·Solv), and differential scanning calorimetry (1) measurements. The Mössbauer analysis supports a description of these compounds as Fe(II) Schiff-base complexes and the occurrence of a metal-centered spin crossover process. In comparison with Fe(III) analogues, it appears that an expanded coordination sphere stabilizes the valence 2+ state of the Fe ion in both complexes. Strong hydrogen-bonding interactions that implicate the phenolato group bound to Fe(II) promote the required extra-stabilization of the S = 2 state and thus determines the spin transition of 1 centered at room temperature. In the lattice, the hydrogen-bonded sites form infinite chains interconnected via a three-dimensional network of intermolecular van der Waals contacts and π-π interactions. Therefore, the spin transition of 1 involves the synergetic influence of electrostatic and elastic interactions, which cause the enhancement of cooperativity and result in the bistability at room temperature.
我们在此聚焦于与席夫碱形成的铁配合物的性质，这些席夫碱参与了铁（III）自旋转变原型的化学过程。中性化合物Fe(pap - 5NO2)2（1）和Fe(qsal - 5NO2)2·Solv（2和2·Solv）（Solv = 2H2O）分别由铁（II）盐与吡啶 - 2 - 甲醛与2 - 羟基 - 5 - 硝基苯胺（Hpap - 5NO2）或5 - 亚硝基水杨醛与喹啉 - 8 - 胺（Hqsal - 5NO2）的缩合产物反应得到。虽然Fe(qsal - 5NO2)2·Solv固体基本上是低自旋（S = 0），需要高于300 K的温度才能发生S = 0 ↔ S = 2的自旋态转换，但Fe(pap - 5NO2)2呈现出强烈协同的一级转变（T↓ = 291 K，T↑ = 308 K），以室温为中心，在10 K时伴有光磁效应（TLIESST = 58 K）。通过单晶X射线衍射（1、100和320 K；2、100 K）、穆斯堡尔谱、红外光谱、紫外可见光谱（1和2·Solv）以及差示扫描量热法（1）测量对这些磁行为进行了研究。穆斯堡尔分析支持将这些化合物描述为铁（II）席夫碱配合物以及发生以金属为中心的自旋交叉过程。与铁（III）类似物相比，似乎扩大的配位球使两种配合物中铁离子的2 + 价态得以稳定。涉及与铁（II）键合的酚氧基的强氢键相互作用促进了S = 2态所需的额外稳定性，从而决定了1在室温下的自旋转变。在晶格中，氢键位点形成通过分子间范德华接触和π - π相互作用的三维网络相互连接的无限链。因此，1的自旋转变涉及静电和弹性相互作用的协同影响，这导致协同性增强并在室温下产生双稳态。
