Chemistry and physics of the novel molecular-based compound exhibiting a spontaneous magnetization below Tc = 14 K, MnCu(obbz).cntdot.1H2O (obbz = oxamidobis(benzoato)). Comparison with the antiferromagnet MnCu(obbz).cntdot.5H2O. Crystal structure and magnetic properties of NiCu(obbz).cntdot.6H2O
Chemistry and physics of the novel molecular-based compound exhibiting a spontaneous magnetization below Tc = 14 K, MnCu(obbz).cntdot.1H2O (obbz = oxamidobis(benzoato)). Comparison with the antiferromagnet MnCu(obbz).cntdot.5H2O. Crystal structure and magnetic properties of NiCu(obbz).cntdot.6H2O
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DOI：
10.1021/ja00197a036
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发表时间：
1989-07
影响因子：
15
通讯作者：
K. Nakatani;J. Carriat;Y. Journaux;O. Kahn;F. Lloret;J. Renard;Y. Pei;J. Sletten;M. Verdaguer
中科院分区：
文献类型：
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作者：
K. Nakatani;J. Carriat;Y. Journaux;O. Kahn;F. Lloret;J. Renard;Y. Pei;J. Sletten;M. Verdaguer
合成了三个化合物MnCu(Obbz)-5H20、MnCu(Obbz)·1H20和NiCu(Obbz)-6H20，分别简称为MnCu5H20、MnCuLH2“和NICU。确定了NICU的晶体结构。NiCu属单斜晶系，空间群为P2/n，晶胞参数为a=7.764(1)，b=12.559(3)，c=20.083(3)，≈=97.56，Z=4。其结构由八面体Ni(II)和草酰胺基桥连的方形平面铜离子组成。NiCu不同于MnCu5H20或MnCu1H20，它们都不是以适合X射线工作的单晶形式获得的。为了获得有关它们结构的信息，我们研究了它们在锰和铜边的XANES和EXAFS谱，以及它们的粉末X射线谱。MnCu5H20和MnCu1H20具有非常相似的结构，前者的化合物中有四个非配位的水分子。Cu(Il)为拉长四方晶系，而Mn(II)为八面体晶系。MnCu5H20和MnCu1H20的第一壳层半径分别为2.17(2)和2.16(2)。这些数据符合如下结构：Mn(II)将被六个氧原子包围；其中两个原子MnCu1H20属于草酰胺基，一个属于羧基，一个属于赤道平面上的水分子；位于顶端的氧原子将属于其他羧基，形成一个二维或三维网络。研究了NICU在4.2-300K温度范围内的磁性能。它们是典型的孤立杂多体，其双四重态能隙37/2等于-156(3)cm“1。MnCu5H20的磁性在4K以下是交替的双金属链的特征，在对T图中具有最小值，即单位MnCu的摩尔磁化率和温度T。在2.3K时，由于三维反铁磁有序，对MnCu5H20产生了一个尖锐的极大值。相反，当T接近临界温度T_c=14K时，MnCu-1H_(20)的T曲线出现偏离，在T_0以下，MnCu-1H_20表现出自发磁化。比较了MnCu5H20和MnCu1H20的磁化强度M随磁场的变化关系。对于这两种化合物，饱和磁化强度对应于每个MnCu单位产生的自旋S=2。此外，在4.2K时，MnCu-1H20表现出软磁的=f(H)磁滞回线特征，并在不同温度下记录了MnCu5H20和MnCu1H20的X带EPR谱，线宽的比较表明，MnCu1H20的磁有序机制是自然的交换作用机制而不是偶极机制。分子基铁磁体的发展前景
The three compounds MnCu (obbz)-5H20, MnCu (obbz)· 1H20, and NiCu (obbz)-6H20, hereafter abbreviated as MnCu-5H20, MnCu-lH2Ó, and NiCu respectively, have been synthesized, obbz stands for oxamidobis (benzoato). The crystal structure of NiCu has been determined. NiCu crystallizes in the monoclinic system, space group P2\/n, with a= 7.764 (1) Á, b= 12.559 (3) Á, c= 20.083 (3) Á, ß= 97.56, and Z= 4. The structure consists of isolated heterodinuclear units with octahedral Ni (II) and square-planar Cu (II) ions bridged by an oxamido group. NiCu is not isomorphous to MnCu-5H20 or to MnCu-lH20, neither of which has been obtained in the formof single crystals suitable for X-ray work. To get information on their structure, we have studied their XANES and EXAFS spectra at both Mn and Cu edges, as well as their powder X-ray patterns. MnCu-5H20 and MnCu-lH20 have very similar structures, with four noncoordinated water molecules in the former compound. Cu (Il) is in elongated tetragonal surroundings and Mn (II) in octahedral surroundings. The radius of the first shell around Mn (II) is equal to 2.17 (2) Á for MnCu-5H20 and 2.16 (2) Á for MnCu-lH20. Those data are consistent with the following structure: Mn (II) would be surrounded by six oxygen atoms; two of these atoms MnCu-lH20 belong to an oxamido group, one to a carboxylato group, and one to a water molecule in the equatorial plane; the oxygen atoms in the apical positions would belong to other carboxylato groups, forming a two-or three-dimensional network. The magnetic properties of NiCu were studied in the 4.2-300K temperature range. They are typical of an isolated heteropair with a doublet-quartet energy gap 37/2 equal to-156 (3) cm" 1. Themagnetic properties of MnCu-5H20, down to 4 K, are characteristics of alternating bimetallic chains with a minimum inthe versus T plot, being the molar magnetic susceptibility per MnCu unit and T the temperature. At 2.3 K, for MnCu-5H20 shows a sharp maximum due to a three-dimensional antiferromagnetic ordering. In contrast, the versus T plot for MnCu-lH20 diverges when T approaches the critical temperature Tc= 14 K. Below T0, MnCu-lH20 exhibits a spontaneous magnetization. The field dependences of the magnetization M for MnCu-5H20 and MnCu-lH20 have been compared. For both compounds, thesaturation magnetization corresponds to a S= 2 resulting spin per MnCu unit. Moreover, MnCu-lH20 at 4.2 K exhibits an= f (H) hysteresis loop characteristicof a soft magnet.The powder X-band EPR spectra of MnCu-5H20 and MnCu-lH20 have been recorded at various temperatures down to 15 K. The comparison of the line widths suggests that the mechanism of the magnetic ordering observed for MnCu-lH20 is of exchange interaction naturerather than of dipolar nature. The perspectives in thefield of the molecular-based ferromagnets