CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF [LN2CU4] HEXANUCLEAR CLUSTERS (WHERE LN = TRIVALENT LANTHANIDE) - MECHANISM OF THE GD(III)-CU(II) MAGNETIC INTERACTION
CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF [LN2CU4] HEXANUCLEAR CLUSTERS (WHERE LN = TRIVALENT LANTHANIDE) - MECHANISM OF THE GD(III)-CU(II) MAGNETIC INTERACTION
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DOI：
10.1021/ja00058a029
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发表时间：
1993-03-10
影响因子：
15
通讯作者：
TROMBE, JC
中科院分区：
文献类型：
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作者：
ANDRUH, M;RAMADE, I;TROMBE, JC
合成了六核簇合物[Ln2Cu4(Fsaaep)4(NO3)6].0.5(CH3OH.H2O)(简写为[Ln2Cu4])，Ln为三价稀土，(Fsaaep)2-为3-(N-2-(吡啶乙基)甲酰亚胺)水杨酸衍生的配体。解析了Ln=Pr的化合物的晶体结构。该化合物属正交晶系，空间群为P2(1)2(1)2(1)。晶格参数为a=18.746(4)埃，b=24.196(4)埃，c=17.053(4)埃，Z=4。结构由[Pr2Cu4]实体组成，其中金属离子形成一个椅子状的六边形。这两个Pr原子位于包含四个铜原子的双层的两侧。铜的环境是拉长的扭曲的八面体，Pr的环境是双折叠的正方形反棱镜。研究了[La2Cu4]和[Gd2Cu4]的磁化率和磁化强度。就磁性而言，六核团簇可以看作是两个独立的Cu(II)Ln(III)Cu(II)三联体。[La2Cu4]的磁化率数据表明，通过闭壳稀土离子的相互作用很弱，相互作用参数为J(CuCu)=-3.13 cm-1(相互作用哈密顿量为H=-JS(A)·S(B))。[Gd_2Cu4]的磁化率数据表明，Cu(II)Gd(III)Cu(II)三元系的基态自旋为S=9/2，Gd(III)-Cu(II)相互作用是铁磁性的，相互作用参数J(GdCu)=6.0 cm-1。在2 K和30 K下测量的磁化强度与磁场的关系证实了基态和Gd(III)-Cu(II)相互作用的性质。本论文的核心是研究Gd(III)-Cu(II)相互作用的机理。这种相互作用的铁磁性质归因于Gd(III)Cu(II)基态组态和Gd(II)Cu(III)电荷转移激发组态之间的耦合，其中一个电子从单占据的3d型铜轨道转移到一个空的5d型Gd轨道。对J(GdCu)进行了半定量估算，与由磁学数据推算的值符合得很好。强调Gd(III)-Cu(II)相互作用是非常特殊的，因为由于4f轨道的收缩，通常涉及4f-3d重叠密度的机制是不起作用的。
The hexanuclear clusters [Ln2Cu4(fsaaep)4(NO3)6].0.5(CH3OH.H2O) (abbreviated as [Ln2Cu4]) have been synthesized; Ln is a trivalent lanthanide and (fsaaep)2- is the ligand deriving from 3-(N-2-(pyridylethyl)formimidoyl)salicylic acid. The crystal structure of the compound with Ln = Pr has been solved. This compound crystallizes in the orthorhombic system, space group P2(1)2(1)2(1). The lattice parameters are a = 18.746(4) angstrom, b = 24.196(4) angstrom, c = 17.053(4) angstrom, and Z = 4. The structure consists of [Pr2Cu4] entities in which the metal ions form a chair-shaped hexagon. The two praseodymium atoms are located on both sides of a double layer containing the four copper atoms. The copper environments are elongated distorted octahedra, and the praseodymium environments are bicapped square antiprisms. The magnetic susceptibility and the magnetization of [La2Cu4] and [Gd2Cu4] have been investigated. As far as the magnetic properties are concerned, the hexanuclear clusters may be viewed as two independent Cu(II)Ln(III)Cu(II) triads. The magnetic susceptibility data for [La2Cu4] have revealed a weak Cu(II)-Cu(II) interaction through the closed-shell rare earth ion characterized by the interaction parameter J(CuCu) = -3.13 cm-1 (the interaction Hamiltonian being of the form H = -JS(A).S(B)). The magnetic susceptibility data for [Gd2Cu4] have shown that the ground-state spin for the Cu(II)Gd(III)Cu(II) triad is S = 9/2; the Gd(III)-Cu(II) interaction is ferromagnetic with an interaction parameter J(GdCu) = 6.0 cm-1. The field dependence of the magnetization measured at both 2 and 30 K confirms the nature of the ground state and of the Gd(III)-Cu(II) interaction. The heart of the paper is devoted to the mechanism of the Gd(III)-Cu(II) interaction. The ferromagnetic nature of this interaction is attributed to the coupling between the Gd(III)Cu(II) ground configuration and the Gd(II)Cu(III) charge-transfer excited configuration in which an electron is transferred from the singly-occupied 3d-type copper orbital toward an empty 5d-type gadolinium orbital. A semiquantitative estimate of J(GdCu) is performed which agrees fairly well with the value deduced from the magnetic data. It is emphasized that the Gd(III)-Cu(II) interaction is quite peculiar in the sense that owing to the contraction of the 4f orbitals the usual mechanisms involving 4f-3d overlap densities are inoperative.