Overgaard Jacob, Rentschler Eva, Timco Grigore A, Larsen Finn K
Department of Chemistry, University of Aarhus, Langelandsgade 140, 8000 Aarhus C, Denmark.
Chemphyschem. 2004 Nov 12;5(11):1755-61. doi: 10.1002/cphc.200400027.
The structure of the complex, [Fe2(II)Fe2(III)(HCOO)10(C6H7N6)n, (1) exhibits a neutral two-dimensional layer network of alternating iron(II) and iron(III) ions, bridged equatorially by formate groups. All iron atoms are octahedrally coordinated, with iron(III) coordinating axially to one gamma-picoline and one formate group, while the iron(II) centers interact axially with two gamma-picoline groups, above and below the layer plane. The complex crystallizes in the triclinic space group P1 at all studied temperatures [at 120 K, the cell dimensions are: a = 10.228(1), b = 12.071(1), c = 12.072(1) A, alpha = 89.801(2), beta = 71.149(2), gamma = 73.371(2) degrees]. An intralayer antiferromagnetic exchange interaction of J = -2.8 cm(-1) between iron(II) and iron(III) was observed in the magnetic studies. Decreasing the temperature to close to 20 K causes a magnetic-ordering phenomenon to occur and a low-temperature phase with a long-range antiferromagnetic spin orientation appears. The magnetic phase transition was confirmed by Mössbauer spectroscopic studies at temperatures above and below the critical temperature. Structural information of 1 from synchrotron X-ray diffraction data collected at room temperature and 16 K suggests that the antiferromagnetic ordering is caused by an enhanced pi-pi interaction between chi-picoline groups from adjacent layers.
配合物[Fe2(II)Fe2(III)(HCOO)10(C6H7N6)n, (1)]的结构呈现出由交替的铁(II)和铁(III)离子组成的中性二维层状网络，甲酸根基团在赤道平面上桥连。所有铁原子均为八面体配位，铁(III)轴向配位一个γ-甲基吡啶和一个甲酸根基团，而铁(II)中心在层平面上方和下方与两个γ-甲基吡啶基团轴向相互作用。该配合物在所有研究温度下均结晶于三斜空间群P1 [在120 K时，晶胞参数为：a = 10.228(1)，b = 12.071(1)，c = 12.072(1) Å，α = 89.801(2)，β = 71.149(2)，γ = 73.371(2)°]。磁性研究中观察到铁(II)和铁(III)之间的层内反铁磁交换相互作用J = -2.8 cm(-1)。将温度降低至接近20 K会导致磁有序现象发生，并出现具有长程反铁磁自旋取向的低温相。在临界温度以上和以下的温度下，通过穆斯堡尔光谱研究证实了磁相变。从室温及16 K收集的同步辐射X射线衍射数据得到的1的结构信息表明，反铁磁有序是由相邻层的χ-甲基吡啶基团之间增强的π-π相互作用引起的。
