Weber Birgit, Kaps Eike, Weigand Jan, Carbonera Chiara, Létard Jean-François, Achterhold Klaus, Parak Fritz G
Department of Chemistry and Biochemistry, Ludwig Maximilian University Munich, Butenandtstrasse 5-13 (Haus D), D-81377 München, Germany.
Inorg Chem. 2008 Jan 21;47(2):487-96. doi: 10.1021/ic070067o. Epub 2007 Dec 21.
Two new spin crossover complexes [FeL(py)(2)] (1) and [FeL(DMAP)(2)] (2) with L being a tetradentate N(2)O(2)(2-) coordinating Schiff-base-like ligand [([3,3']-[1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentanedionato)(2-)-N,N',O(2),O(2)'], py = pyridine and DMAP = p-dimethylaminopyridine have been investigated using temperature-dependent susceptibility and thermogravimetric and photomagnetic measurements as well as Mössbauer spectroscopy and X-ray structure analysis. Both complexes show a cooperative spin transition with an approximately 9 K wide thermal hysteresis loop in the case of 2 (T(1/2) upward arrow = 183 K and T(1/2) downward arrow = 174 K) and an approximately 2 K wide thermal hysteresis loop in the case of the pyridine diadduct 1 (T(1/2) upward arrow = 191 K and T(1/2) downward arrow = 189 K). The spin transition was additionally followed by different temperature-scanning calorimetry and Mössbauer spectroscopy for 2, and a good agreement for the transition temperatures obtained with the different methods was found. Results from X-ray structure analysis indicate that the cooperative interactions are due to elastic interactions in both compounds. They are more pronounced in the case of 2 with very short intermolecular iron-iron distances of 7.2 A and several intense C-C contacts. The change of the spin state at the iron center is accompanied by a change of the O-Fe-O angle, the so-called bit of the equatorial ligand, from 108 degrees in the high-spin state to 90 degrees in the low-spin state. The reflectivity measurements of both compounds give at low temperature indication that at the sample surface the light-induced excited spin state trapping (LIESST) effect occurs. In bulk condition using a SQUID magnetometer the complex 2 displays some photomagnetic properties with an photoexcitation level of 60% and a T(LIESST) value of 53 K.
研究了两种新型自旋交叉配合物[FeL(py)₂] (1) 和[FeL(DMAP)₂] (2)，其中L为四齿N₂O₂²⁻配位的类席夫碱配体[([3,3']-[1,2-亚苯基双(亚氨基次甲基)]双(2,4-戊二酮)(2-)-N,N',O₂,O₂']，py = 吡啶，DMAP = 对二甲氨基吡啶，采用了变温磁化率、热重和光磁测量以及穆斯堡尔光谱和X射线结构分析。两种配合物均显示出协同自旋转变，对于2，热滞回线约为9 K宽（T₁/₂向上箭头 = 183 K，T₁/₂向下箭头 = 174 K），对于吡啶加合物1，热滞回线约为2 K宽（T₁/₂向上箭头 = 191 K，T₁/₂向下箭头 = 189 K）。对于2，还通过不同的温度扫描量热法和穆斯堡尔光谱跟踪自旋转变，发现不同方法获得的转变温度吻合良好。X射线结构分析结果表明，协同相互作用是由于两种化合物中的弹性相互作用。在2中更为明显，分子间铁 - 铁距离非常短，为7.2 Å，还有几个强烈的C - C接触。铁中心自旋态的变化伴随着赤道配体的O - Fe - O角（即所谓的“位”）从高自旋态的108°变为低自旋态的90°。两种化合物的反射率测量在低温下表明，在样品表面发生了光诱导激发自旋态捕获（LIESST）效应。在使用超导量子干涉仪磁强计的体相条件下，配合物2显示出一些光磁性质，光激发水平为60%，T(LIESST)值为53 K。
