Okada Keiji, Nagao Osami, Mori Hiroki, Kozaki Masatoshi, Shiomi Daisuke, Sato Kazunobu, Takui Takeji, Kitagawa Yasutaka, Yamaguchi Kizashi
Departments of Chemistry and Materials Science, Graduate School of Science, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
Inorg Chem. 2003 May 19;42(10):3221-8. doi: 10.1021/ic0207193.
Mn(hfac)(2) complexes of [2-(5-pyrimidinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H- imidazoline-1-oxyl 3-oxide] (1) and its 2-(3-pyridyl) analogue (2) were prepared. Both complexes formed similar dimer structures. However, their packing patterns were considerably different. The pyrimidine dimers were aligned to form a linear chain structure, and each dimer was weakly bound by two sets of O6-C2 short contacts. In the pyridine dimer complex, two structurally similar but independent dimers were alternatively arranged, and two dimer-dimer contacts, O6-C2 (3.13 A) and O6-C3 (3.30 A), were observed. The pyrimidine complex showed strong antiferromagnetic behavior in the high temperature region (150-300 K) and weak ferromagnetic behavior below 100 K. Two models were used to analyze these magnetic properties. One is a quintet-septet thermal equilibrium model with mean-field approximation, which can reproduce the round minimum observed at about 150 K in chi(p)T plots (J(1)/k(B) = -148 +/- 2 K with theta = +2.5 +/- 0.1 K). The other is a ferromagnetic S = 2 chain model to fit the chi(p)T values in the lower temperature region (J(S=2)/k(B) = +0.31 +/- 0.01 K). The pyridine complex showed antiferromagnetic interactions both in the high and low temperature regions. The magnetic behavior was similarly analyzed with the following parameters: J(1)/k(B) = -140 +/- 2 K with theta = -0.55 +/- 0.05 K, and J(S=2)/k(B) = -0.075 +/- 0.003 K. The ligand-ligand interactions for both of the complexes were theoretically analyzed. The calculated results agreed well with the experiments. The stronger antiferromagnetic behavior observed in both the complexes at high temperatures was attributed to the magnetic interaction between the Mn(II) and the coordinating nitroxide oxygen atom. The weaker ferromagnetic interaction, J(S=2)/k(B) = +0.31 +/- 0.01 K, in the pyrimidine complex was attributed to the coulombic O6-C2 contact. Antiferromagnetic interaction J(S=2)/k(B) = -0.075 +/- 0.003 K in the pyridine complex was attributed to the O6-C3 contact.
制备了2-(5-嘧啶基)-4,4,5,5-四甲基-4,5-二氢-1H-咪唑啉-1-氧基 3-氧化物及其 2-(3-吡啶基)类似物(2)的 Mn(hfac)(2)配合物。两种配合物都形成了相似的二聚体结构。然而，它们的堆积模式有很大不同。嘧啶二聚体排列形成线性链结构，每个二聚体通过两组 O6-C2 短接触弱结合。在吡啶二聚体配合物中，两个结构相似但独立的二聚体交替排列，观察到两个二聚体-二聚体接触，O6-C2(3.13 Å)和 O6-C3(3.30 Å)。嘧啶配合物在高温区域(150 - 300 K)表现出强反铁磁行为，在 100 K 以下表现出弱铁磁行为。使用两种模型分析这些磁性性质。一种是具有平均场近似的五重态-七重态热平衡模型，它可以重现χ(p)T 图中在约 150 K 处观察到的圆形最小值(J(1)/k(B)= -148 ± 2 K，θ = +2.5 ± 0.1 K)。另一种是铁磁 S = 2 链模型，用于拟合低温区域的χ(p)T 值(J(S=2)/k(B)= +0.31 ± 0.01 K)。吡啶配合物在高温和低温区域均表现出反铁磁相互作用。用以下参数类似地分析了磁性行为：J(1)/k(B)= -140 ± 2 K，θ = -0.55 ± 0.05 K，以及 J(S=2)/k(B)= -0.075 ± 0.003 K。对两种配合物的配体-配体相互作用进行了理论分析。计算结果与实验结果吻合良好。两种配合物在高温下观察到的较强反铁磁行为归因于 Mn(II)与配位氮氧化物氧原子之间的磁相互作用。嘧啶配合物中较弱的铁磁相互作用 J(S=2)/k(B)= +0.31 ± 0.01 K 归因于库仑 O6-C2 接触。吡啶配合物中的反铁磁相互作用 J(S=2)/k(B)= -0.075 ± 0.003 K 归因于 O6-C3 接触。
