Antiferromagnetic versus ferromagnetic exchange interactions in bis(μ-O(oximate))dinickel(II) units for a series of closely related cube shaped carboxamideoximate-bridged Ni(4) complexes. A combined experimental and theoretical magneto-structural study.
Antiferromagnetic versus ferromagnetic exchange interactions in bis(μ-O(oximate))dinickel(II) units for a series of closely related cube shaped carboxamideoximate-bridged Ni(4) complexes. A combined experimental and theoretical magneto-structural study.
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DOI：
10.1021/ic101435b
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发表时间：
2010-11
影响因子：
4.6
通讯作者：
M. Palacios;A. Mota;Jesus E. Perea-Buceta;Fraser J. White;E. Brechin;E. Colacio
中科院分区：
文献类型：
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作者：
M. Palacios;A. Mota;Jesus E. Perea-Buceta;Fraser J. White;E. Brechin;E. Colacio
本文报道了三种四金属Ni(II)簇合物的合成、晶体结构、实验和理论磁化学表征，即[Ni(4)(L)(4)(Cl)(2)(MeOH)(2)](ClO(4))(2)·4MeOH(1)，[Ni(4)(L)(4)(N(3))(2)(MeOH)(2)](ClO(4))(2)·2MeOH(2)，和[Ni(4)(L1)(4)(pyz)(2)(PhCOO)(2)(MeOH)(2)](ClO(4))(2)·7MeOH(3)(其中HL和HL1分别代表联吡啶-2-甲胺和嘧啶-2-甲胺)。在这些化合物的Ni(4)(2+)单元中，扭曲的八面体Ni(II)离子被羧胺亚胺配体桥联，形成扭曲的四面体排列。具有C(2)对称性的Ni(4)(2+)单元也可以看作是以单[O原子]和双[NO肟基]桥基为原子边的立方体，它定义了两个几乎正方形的Ni(O)(2)Ni环和四个不规则的六方Ni(NO)(2)Ni环。为了分析1-3的磁性，我们考虑了最简单的双J模型，其中J(1)=J(2)(属于Ni(O)(2)Ni方环的Ni(II)离子之间的交换作用)和J(A)=J(B)=J(C)=J(D)(属于Ni-(NO)(2)Ni六方环的Ni(II)离子之间的交换作用)，其中哈密顿H=-J(1)(S(1)S(2)+S(3)S(4))-J(A)(S(1)S(3)+S(1)S(4)+S(2)S(3)+S(2)S(4)由实验磁化率数据拟合得到的J(1)和J(A)值分别为-5.8 cm(-1)和-22.1 cm(-1)；磁结构结果和密度泛函理论计算表明，Ni(μ-O)(2)Ni方环内的交换作用取决于Ni-O-Ni桥角(θ)和NO桥基团相对于Ni(O)(2)Ni平面的离面夹角(τ)，而通过定义六角环侧面的Ni-N-O(Ni)-Ni交换路径传播的相互作用取决于Ni-N-O-Ni扭转角(α)。在这两种情况下，都获得了理论磁-结构关联，这使得可以预测预期的铁磁相互作用的角度。对于化合物3，除了θ角和τ角外，通过苯甲酸桥的轴向磁交换路径的存在也可能通过轨道反互补对该化合物中观察到的F相互作用做出贡献，这一点得到了密度泛函计算的支持。密度泛函理论计算表明，随着Ni(μ-O)(2)Ni方环O-Ni-O面间二面角的增大，反铁磁交换增大。
The syntheses, crystal structures, and the experimental and theoretical magnetochemical characterization for three tetrametallic Ni(II) clusters, namely, [Ni(4)(L)(4)(Cl)(2)(MeOH)(2)](ClO(4))(2)·4MeOH (1), [Ni(4)(L)(4)(N(3))(2)(MeOH)(2)](ClO(4))(2)·2MeOH (2), and [Ni(4)(L1)(4)(pyz)(2)(PhCOO)(2)(MeOH)(2)](ClO(4))(2)·7MeOH (3) (where HL and HL1 represent bipyridine-2-carboxamideoxime and pyrimidine-2-carboxamideoxime, respectively) are reported. Within the Ni(4)(2+) units of these compounds, distorted octahedral Ni(II) ions are bridged by carboxamideoximato ligands to adopt a distorted tetrahedral disposition. The Ni(4)(2+) unit, of C(2) symmetry, can also be viewed as a cube with single [O-atom] and double [NO oxime] bridging groups as atom edges, which define two almost square-planar Ni(O)(2)Ni rings and four irregular hexagonal Ni(NO)(2)Ni rings. To analyze the magnetic properties of 1-3, we have considered the simplest two-J model, where J(1) = J(2) (exchange interactions between the Ni(II) ions belonging to the Ni(O)(2)Ni square rings) and J(a) = J(b) = J(c) = J(d) (exchange interactions between the Ni(II) ions belonging to the Ni-(NO)(2)Ni hexagonal rings) with the Hamiltonian H = -J(1)(S(1)S(2) + S(3)S(4)) - J(a)(S(1)S(3) + S(1)S(4) + S(2)S(3) + S(2)S(4)). The J(1) and J(a) values derived from the fitting of the experimental susceptibility data are -5.8 cm(-1) and -22.1 cm(-1) for 1; -2.4 cm(-1) and -22.8 cm(-1) for 2, and +15.6 cm(-1) and -10.8 cm(-1) for 3. The magneto-structural results and density-functional theory (DFT) calculations demonstrate that the exchange interactions inside the Ni(μ-O)(2)Ni square rings depend on the Ni-O-Ni bridging angle (θ) and the out-of-plane angle of the NO oximate bridging group with respect to the Ni(O)(2)Ni plane (τ), whereas the interactions propagated through the Ni-N-O(Ni)-Ni exchange pathways defining the side of the hexagonal rings depend on the Ni-N-O-Ni torsion angle (α). In both cases, theoretical magneto-structural correlations were obtained, which allow the prediction of the angle for which ferromagnetic interactions are expected. For compound 3, the existence of the axial magnetic exchange pathway through the syn-syn benzoate bridge may also contribute (in addition to the θ and τ angles) to the observed F interaction in this compound through orbital countercomplementarity, which has been supported by DFT calculations. Finally, DFT calculations clearly show that the antiferromagnetic exchange increases when the dihedral angle between the O-Ni-O planes of the Ni(μ-O)(2)Ni square ring, β, increases.