Novel chiral three-dimensional iron(III) compound exhibiting magnetic ordering at T(c) = 40 K.
Novel chiral three-dimensional iron(III) compound exhibiting magnetic ordering at T(c) = 40 K.
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DOI：
10.1021/ic011100o
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发表时间：
2002-03
影响因子：
4.6
通讯作者：
D. Armentano;G. De Munno;F. Lloret;A. Palii;M. Julve
中科院分区：
文献类型：
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作者：
D. Armentano;G. De Munno;F. Lloret;A. Palii;M. Julve
本文报道了式[（NH（4））（2）[Fe（2）O（ox）（2）Cl（2）]·2 H（2）O]（n）（1）（ox =草酸根二价阴离子）的铁（III）化合物的制备和晶体结构测定。配合物1属于正交晶系，空间群Fdd 2，a = 14.956（7）A，B = 23.671（9）A，c = 9.026（4）A，Z = 8。配合物1的结构是由手性阴离子三维网络[Fe（2）O（ox）（2）Cl（2）]（2-）组成，其中Fe（III）离子通过单氧代和双二齿双氧代基团连接。通过这些桥连配体的金属-金属分离分别为3.384（2）和5.496（2）A。铵阳离子和结晶水分子位于由铁原子限定的螺旋准六边形隧道中。赝六边形隧道中最长的铁-铁距离为15.778（2），最短的铁-铁距离为8.734（2）。铁原子是六配位的：一个末端氯配位体和五个氧原子，氧代基团的氧原子和四个来自两个顺式配位的草酸盐配位体，在金属原子周围建立了一个扭曲的八面体环境。Fe-O（oxo）键距[1.825（2）A]明显短于Fe（III）-O（ox）键距[平均值2.103（4）A]和Fe（III）-Cl键距[2.314（2）A]。在2.0-300 K的温度范围内的磁化率测量结果表明，在195 K处出现磁化率最大值，并在T（c）= 40 K的较低温度区向磁有序态转变。通过氧桥的强反铁磁耦合（J = -46.4 cm（-1），哈密顿量为H = -JS（A）.S（B））解释了磁化率最大值，而由于手性三维网络内的反对称磁交换引起的约0.3度的弱自旋倾斜解释了磁有序。由1在5 K时的磁滞回线获得的矫顽场（H（c））和剩余磁化强度（M（r））的值为4000 G和0.016 μ（B）。
The preparation and crystal structure determination of the iron(III) compound of formula [(NH(4))(2)[Fe(2)O(ox)(2)Cl(2)].2H(2)O](n) (1) (ox = oxalate dianion) are reported here. Complex 1 crystallizes in the orthorhombic system, space group Fdd2, with a = 14.956(7) A, b = 23.671(9) A, c = 9.026(4) A, and Z = 8. The structure of complex 1 consists of the chiral anionic three-dimensional network [Fe(2)O(ox)(2)Cl(2)](2-) where the iron(III) ions are connected by single oxo and bisbidentate oxalato groups. The metal-metal separations through these bridging ligands are 3.384(2) and 5.496(2) A, respectively. Ammonium cations and crystallization water molecules are located in the helical pseudohexagonal tunnels defined by iron atoms. The longest iron-iron distance in the pseudohexagonal tunnel is 15.778(2) A whereas the shortest one is 8.734(2) A. The iron atoms are hexacoordinated: a terminal chloro ligand and five oxygen atoms, that of the oxo group and four from two cis coordinated oxalate ligands, build a distorted octahedral environment around the metal atom. The Fe-O(oxo) bond distance [1.825(2) A] is significantly shorter than the Fe(III)-O(ox) [average value 2.103(4) A] and Fe(III)-Cl bond distances [2.314(2) A]. Magnetic susceptibility measurements of 1 in the temperature range 2.0-300 K reveal the occurrence of a susceptibility maximum at 195 K and a transition toward a magnetically ordered state in the lower temperature region with T(c) = 40 K. The strong antiferromagnetic coupling through the oxo bridge (J = -46.4 cm(-1), the Hamiltonian being H = -JS(A).S(B)) accounts for the susceptibility maximum whereas a weak spin canting of approximately 0.3 degrees due to the antisymmetric magnetic exchange within the chiral three-dimensional network is responsible for the magnetic ordering. The values of coercive field (H(c)) and remnant magnetization (M(r)) obtained from the hysteresis loop of 1 at 5 K are 4000 G and 0.016 micro(B).