Weber Birgit, Kaps Eike S, Obel Jaroslava, Achterhold Klaus, Parak Fritz G
Ludwig Maximilian University Munich, Department of Chemistry and Biochemistry, Butenandtstr. 5-13 (Haus F), D-81377 Munchen, Germany.
Inorg Chem. 2008 Nov 17;47(22):10779-87. doi: 10.1021/ic801388a. Epub 2008 Oct 21.
The magnetic properties and results from X-ray structure analysis for a new pair of iron(II) spin-crossover complexes FeL1(meim) 2 ( 1(meim)) and Fe 2L2(meim) 4 4 ( 2(meim) 4), with L1 being a tetradentate N 2O 2 (2-) coordinating Schiff-base-like ligand [([3,3']-[1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentane-dionato)(2-)N,N',O (2),O (2)'], L2 being an octadentate, dinucleating N 2O 2 (2-) coordinating Schiff-base-like ligand [3,3',3'',3''']-[1,2,4,5-phenylenetetra(iminomethylidyne)]tetra(2,4-pentanedionato)(2-) N, N', N'', N''', O (2), O (2) ', O (2) '', O (2) '''], and meim being N-methylimidazole, are discussed in this work. Crystalline samples of both complexes show a cooperative spin transition with an approximately 2-K-wide thermal hysteresis loop in the case of 1(meim) ( T 1/2 increase = 179 K and T 1/2 decrease = 177 K) and an approximately 21-K-wide thermal hysteresis loop in the case of dinuclear complex 2(meim) 4 ( T 1/2 increase= 199 K and T 1/2 decrease= 178 K). For a separately prepared powder sample of 2, a gradual spin transition with T 1/2 = 229 K is observed that was additionally followed by Mossbauer spectroscopy. The results from X-ray structure analysis give a deeper insight into the molecule packing in the crystal and, by this, help to explain the increase of cooperative interactions during the spin transition when going from the mononuclear to the dinuclear complex. Both compounds crystallize in the triclinic space group P1, and the X-ray structure was analyzed before and after the spin transition. The change of the spin state at the iron center is accompanied by a change of the O-Fe-O angle, the so-called bite of the equatorial ligand, from about 109 degrees in the high-spin state to 89 degrees in the low-spin state. The cooperative interactions responsible for the thermal hysteresis loop are due to elastic interactions between the complex molecules in both cases. However, due to the higher symmetry of the dinucleating ligand in 2(meim) 4, a 3D network of short contacts is formed, while for mononuclear complex 1(meim), a 2D layer of linked molecules is observed. The spin transition was additionally followed in solution using (1)H NMR spectroscopy for both complexes. In both cases, a gradual spin transition is observed, and the increase of cooperative interactions when going from the mononuclear to the dinuclear system is solely attributed to the extended network of intermolecular contacts.
本文讨论了一对新的铁（II）自旋交叉配合物FeL1(meim)₂（1(meim)）和Fe₂L₂(meim)₄₄（2(meim)₄）的磁性以及X射线结构分析结果，其中L1是一种四齿N₂O₂(2-)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-戊二酮基)(2-)N,N',O(2),O(2)']，L2是一种八齿、双核N₂O₂(2-)配位的类席夫碱配体[3,3',3'',3''']-[1,2,4,5-亚苯基四(亚氨基次甲基)]四(2,4-戊二酮基)(2-)N,N',N'',N''',O(2),O(2)',O(2)'',O(2)''']，meim是N-甲基咪唑。两种配合物的晶体样品均显示出协同自旋转变，对于1(meim)，其热滞回线宽度约为2 K（T₁/₂增加 = 179 K，T₁/₂降低 = 177 K）；对于双核配合物2(meim)₄，热滞回线宽度约为21 K（T₁/₂增加 = 199 K，T₁/₂降低 = 178 K）。对于单独制备的2的粉末样品，观察到其具有T₁/₂ = 229 K的逐渐自旋转变，并通过穆斯堡尔光谱进行了进一步研究。X射线结构分析结果更深入地揭示了晶体中的分子堆积情况，从而有助于解释从单核配合物到双核配合物自旋转变过程中协同相互作用的增强。两种化合物均结晶于三斜空间群P1，并在自旋转变前后对其X射线结构进行了分析。铁中心自旋态的变化伴随着O-Fe-O角（即赤道配体的所谓咬角）从高自旋态的约109度变为低自旋态的89度。在这两种情况下，导致热滞回线的协同相互作用均源于配合物分子之间的弹性相互作用。然而，由于2(meim)₄中双核配体具有更高的对称性，形成了一个短接触的三维网络，而对于单核配合物1(meim)，则观察到一个二维连接分子层。还使用¹H NMR光谱对两种配合物在溶液中的自旋转变进行了跟踪。在两种情况下，均观察到逐渐的自旋转变，并且从单核体系到双核体系协同相互作用的增强完全归因于分子间接触的扩展网络。
