School of Chemistry, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima, 30000, Thailand.
Dalton Trans. 2010 Dec 7;39(45):10900-9. doi: 10.1039/c0dt00447b. Epub 2010 Aug 19.
Four new Fe(II) coordination polymers of formulation [Fe(L)(3)]MCl(4), M = Fe(III), In(III) have been synthesized and structurally and magnetically characterized. They contain organodinitrile bridging ligands where L is 1,1'-azobiscyclopentanecarbonitrile (ACCN) or 2,2'-azobisisobutyronitrile (AIBN). The compounds are [Fe(AIBN)(3)]InCl(4) (1), [Fe(AIBN)(3)]FeCl(4) (2), [Fe(ACCN)(3)]InCl(4) (3), and [Fe(ACCN)(3)]FeCl(4) (4). Compounds 1 and 2 were first reported many years ago, elsewhere, but not then structurally characterized. All four compounds adopt an "open framework" α-Po type 3D lattice structure with the M(III)Cl(4) anions held in the channels thereof. There are two crystallographically independent, distorted octahedral Fe(II)N(6) sites in 1 and 2, but only one Fe(II) site in 3 and 4. These are the first open framework systems containing covalently linked dinitrile bridging ligands and join a related class of Fe(L)(3) frameworks known with ditriazole and ditetrazole linkers and exhibiting spin crossover behaviour. Indeed, compounds 1 and 2 display a 'half' spin transition in their magnetic susceptibility vs. temperature plots, this being due to the fact that only half of the Fe(II) d(6) centres in the framework changed spin from HS → LS as the temperature decreased, as also evidenced by the structural details around the Fe(II) centres, determined below T(1/2) (118 and 170 K for 1 and 2, respectively). Mössbauer spectra confirmed these spin changes. The weak cooperativity between the SCO centres led to a lack of thermal hysteresis. When the ACCN ligand was used instead of the AIBN ligand, in compounds 3 and 4, only one crystallographically unique Fe(II) centre was observed in an otherwise similar framework. No SCO transition was observed in 3 and 4 as evidenced by temperature independent moment data, backed up by single crystal X-ray crystallographic analysis at 123 K. Thus the HS Fe(II) ions remain in this spin state at all temperatures, presumably because the ligand field, at the nitrile N-donors, is weaker in ACCN than in AIBN. In addition, the crystal structure of a minor phase of an aqua complex, [Fe(AIBN)(2)(H(2)O)(2)]FeCl(4) (2a), obtained from the reaction that produced 2, showed a 2D layer motif, with trans-Fe(N)(4)(H(2)O)(2) ligation.
四种新的[Fe(L)(3)]MCl(4)（M = Fe(III)，In(III)）配位聚合物已被合成并进行了结构和磁性表征。它们包含有机二腈桥联配体，其中 L 为 1,1'-偶氮二环戊烷甲腈（ACCN）或 2,2'-偶氮异丁腈（AIBN）。这些化合物为[Fe(AIBN)(3)]InCl(4)（1）、[Fe(AIBN)(3)]FeCl(4)（2）、[Fe(ACCN)(3)]InCl(4)（3）和[Fe(ACCN)(3)]FeCl(4)（4）。化合物 1 和 2 多年前曾在其他地方首次报道过，但当时并未进行结构表征。所有四种化合物均采用“开放式框架”α-Po 型 3D 晶格结构，M(III)Cl(4)阴离子位于通道中。在 1 和 2 中存在两个结晶学上独立的、扭曲的八面体 Fe(II)N(6)位点，但在 3 和 4 中只有一个 Fe(II)位点。这些是第一个含有共价连接二腈桥联配体的开放式框架系统，加入了一类具有三唑和四唑连接体并表现出自旋交叉行为的相关Fe(L)(3)框架。事实上，化合物 1 和 2 在其磁化率与温度关系图中显示出“半”自旋跃迁，这是由于框架中只有一半的 Fe(II)d(6)中心随着温度的降低从 HS→LS 改变自旋，这也可以从 Fe(II)中心周围的结构细节中得到证明，在 T(1/2)（分别为 118 和 170 K）以下确定。穆斯堡尔光谱证实了这些自旋变化。SCO 中心之间的弱协同作用导致缺乏热滞后。当使用 ACCN 配体代替 AIBN 配体时，在化合物 3 和 4 中，在其他方面相似的框架中仅观察到一个结晶学上独特的 Fe(II)中心。由于温度独立的磁矩数据证实，在 3 和 4 中没有观察到 SCO 跃迁，这得到了单晶 X 射线晶体学分析在 123 K 下的支持。因此，HS Fe(II)离子在所有温度下都保持这种自旋状态，可能是因为在 ACCN 中，配体场在腈氮供体上比在 AIBN 中弱。此外，从产生 2 的反应中获得的水合配合物[Fe(AIBN)(2)(H(2)O)(2)]FeCl(4)（2a）的次要相的晶体结构显示出二维层状图案，具有反式-Fe(N)(4)(H(2)O)(2)配位。
