Pentacobalt EMACs [Co5(μ5-dpzpda)4X2] (X = Clâ (1), NCSâ (2)) with fine-tuning of the supporting ligand based on the tripyridyldiamine ligand, N,Nâ²-di(pyrazin-2-yl)pyridine-2,6-diamine (H2dpzpda), and their reduced form (Ph4P)[Co5(μ5-dpzpda)4X2] (X = Clâ (3), NCSâ (4)) were first synthesized and structurally characterized. The structures of 1â4 showed direct CoâCo bonds with CoâCo distances in the range 2.2385(7)â2.2888(15) Ã
, and valence electrons delocalized through the whole metal chain with distances of longer than 9.06 Ã
. The distances of the inner CoâCo bonds and the Coâaxial ligands became longer after reduction, whereas no significant change was observed in the distances of the outer CoâCo bonds and CoâN (supporting ligand) bonds, which was consistent with the MO analysis. Electrochemical studies on both 1 and 2 showed one reversible oxidation and one reversible reduction at E1/2 = +0.82 and â0.05 V for 1, and at E1/2 = +0.89 and +0.02 V for 2, respectively. The redox reactions of the thiocyanate complex 4 happened at higher potentials than the chloride complex 3. A magnetism study of 1â4 revealed anomalous magnetic behaviour similar to that of heptacobalt EMACs, and a deviation from the CurieâWeiss law was observed. The ÏMT value at 300 K is 0.84 and 1.16 emu K molâ1 for 1 and 2, respectively, suggesting spin-equilibrium or a spin-admixture between doublet and quartet states arising from the Boltzmann distribution over different energy levels. Similar results were obtained for 3 and 4, showing intermediate ÏMT values between a diamagnetic and a triplet state of 0.15â0.96 emu K molâ1 in the temperature range 5â300 K. The structural and magnetic results were interpreted through an EHMO study.
五
钴 EMAC [Co5(μ5-dpzpda)4X2] (X = Cl-(1),
NCS-(2)),并基于三
吡啶二胺
配体 N,N-di(
吡嗪-2-基)
吡啶-2,6-二胺 (H2dpzpda) 及其还原形式 (Ph4P)[Co5(μ5-dpzpda)4X2] (X = Cl– (3),
NCS– (4))首先进行了合成并进行了结构表征。 1–4 的结构显示出直接的 Co–Co 键,Co–Co 距离在 2.2385(7)–2.2888(15) – 范围内,价电子在整个
金属链中离域,距离大于9.06 ×。还原后,内部Co-Co键和Co-轴
配体的距离变长,而外部Co-Co键和Co-N(支持
配体)键的距离没有观察到显着变化,这与 MO 分析一致。对 1 和 2 的电
化学研究表明,1 的 E1/2 = +0.82 和 ±0.05 V 时有一种可逆氧化,2 的 E1/2 = +0.89 和 +0.02 V 时有一种可逆还原。
硫氰酸盐配合物 4 的氧化还原反应发生在比
氯化物配合物 3 更高的电势下。1–4 的磁性研究揭示了与七
钴 EMAC 类似的异常磁性行为,并观察到与居里-韦斯定律的偏差。 1 和 2 在 300 K 时的
MT 值分别为 0.84 和 1.16 emu K MOl-1,这表明在不同能级上的玻尔兹曼分布产生的双重态和四重态之间的自旋平衡或自旋混合。 3 和 4 也获得了类似的结果,显示在 5–300 K 的温度范围内,抗磁性和三重态之间的中间 δ
MT 值为 0.15–0.96 emu K MOl–1。结构和磁性结果为通过 EHMO 研究进行解释。