Experimental and Theoretical Study of the Antisymmetric Magnetic Behavior of Copper inverse-9-Metallacrown-3 Compounds

Use of PhPyCNO−/X− “blends” (PhPyCNOH = phenyl 2-pyridyl ketoxime; X− = OH−, alkanoato, ClO4−) in copper chemistry yielded trinuclear clusters that have been characterized as inverse-9-metallacrown-3 compounds and accommodate one or two guest ligands. The magnetic behavior showed a large antiferromagnetic interaction and a discrepancy between the low-temperature magnetic behavior observed experimentally and that predicted from a magnetic model. The discrepancy between the Brillouin curve and the experimental result provides clear evidence of the influence of the antisymmetric interaction. Introducing the antisymmetric terms derived from the fit of the susceptibility data into the magnetization formula caused the simulated curve to become nearly superimposable on the experimental one. The EPR data indicated that the compound [Cu3(PhPyCNO)3(μ3-OH)(2,4,5-T)2] (1), where 2,4,5-T is 2,4,5-trichlorophenoxyacetate, has isosceles or lower magnetic symmetry (δ ≠ 0), that antisymmetric exchange is important (G ≠ 0), and that ΔE > hν. The structures of the complexes 1 and [Cu3(PhPyCNO)3(μ3-OH)(H2O)(ClO4)2] (2) were determined using single-crystal X-ray crystallography. Theoretical calculations based on density functional theory were performed using the full crystal structures of 1, 2, [Cu3(PhPyCNO)3(OH)(CH3OH)2(ClO4)2] (3), and [Cu3(PhPyCNO)3(μ3-OMe)(Cl)(ClO4)] (4). The geometries of the model compounds [Cu3(κ3N,N,O-HNCHCHNO)3(μ3-OH)(μ2-HCOO)(HCOO)] (5), [Cu3(κ3N,N,O-HNCHCHNO)3(μ2-HCOO)(HCOO)]+ (6), [Cu3(κ3N,N,O-HNCHCHNO)3(μ3-O)]+ (7), and [Cu3(κ3N,N,O-HNCHCHNO)3]3+ (8) were optimized at the same level of theory for both the doublet and quartet states, and vibrational analysis indicated that the resulting equilibrium geometries corresponded to minima on the potential energy surfaces. Both eg and t2g magnetic orbitals seem to contribute to the magnetic exchange coupling. The latter contribution, although less important, might be due to overlap of the t2g orbitals with the p-type orbitals of the central triply bridging oxide ligand, thereby affecting its displacement from the Cu3 plane and contributing to the antiferromagnetic coupling. The crucial role of the triply bridging oxide (μ3-O) ligand on the antiferromagnetic exchange coupling between the three Cu(II) magnetic centers is further evidenced by the excellent linear correlation of the coupling constant J with the distance of the μ3-O ligand from the centroid of the Cu3 triangle.

利用PhPyCNO−/X−“混合物”（PhPyCNOH = 苯基2-吡啶基甲酰肟；X− = OH−, 烷酸根，ClO4−）在铜化学中的应用，成功制备了具有逆-9-金属冠-3结构的核簇化合物，这些化合物能够容纳一个或两个配体。其磁性表现显示出显著的抗铁磁性相互作用，以及实验观察到的低温磁性行为与基于磁性模型的预测之间存在差异。布里渊曲线与实验结果的差异提供了不对称相互作用影响的明确证据。将拟合磁化率数据得到的非对称项引入磁化公式中，导致模拟曲线与实验曲线几乎完全重合。电子顺磁共振（EPR）数据表明，化合物[Cu3(PhPyCNO)3(μ3-OH)(2,4,5-T)2]（1），其中2,4,5-T代表2,4,5-三氯苯氧基乙酸，具有等腰或较低磁对称性（δ ≠ 0），非对称交换作用至关重要（G ≠ 0），且ΔE > hν。复合物1和[Cu3(PhPyCNO)3(μ3-OH)(H2O)(ClO4)2]（2）的结构是通过单晶X射线晶体学确定的。基于密度泛函理论，对1、2、[Cu3(PhPyCNO)3(OH)(CH3OH)2(ClO4)2]（3）和[Cu3(PhPyCNO)3(μ3-OMe)(Cl)(ClO4)]（4）的全晶体结构进行了理论计算。模型化合物[Cu3(κ3N,N,O-HNCHCHNO)3(μ3-OH)(μ2-HCOO)(HCOO)]（5）、[Cu3(κ3N,N,O-HNCHCHNO)3(μ2-HCOO)(HCOO)]+（6）、[Cu3(κ3N,N,O-HNCHCHNO)3(μ3-O)]+（7）和[Cu3(κ3N,N,O-HNCHCHNO)3]3+（8）的几何结构在相同理论水平上进行了优化，以双态和四态状态为基准，振动分析表明所得到的平衡几何结构对应于势能面上的极小值。eg和t2g磁轨道似乎都对磁交换耦合有贡献。后者的贡献，尽管相对较小，可能是由于t2g轨道与中心三桥连氧化物配体的p型轨道重叠，从而影响其相对于Cu3平面的位移，并有助于反铁磁性耦合。三桥连氧化物（μ3-O）配体在三个Cu(II)磁性中心之间的反铁磁性交换耦合中的关键作用，进一步得到了耦合常数J与μ3-O配体从Cu3三角形质心距离之间优秀线性相关性的证实。