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首页> 外文期刊>Chemistry: A European journal >A New Class of Ferromagnetically-Coupled Mixed Valence Vanadium(IV/V) Polyoxometalates
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A New Class of Ferromagnetically-Coupled Mixed Valence Vanadium(IV/V) Polyoxometalates

机译：新型的铁磁耦合混合价钒（IV / V）多金属氧酸盐

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摘要

Reaction of [V~(VI)OCl_2(thf)_2] with a bidentate nitrogen-donor ligand (L: phen = 1,10-phenanthroline, 5-mephen = 5-methyl-1,10-phenanthroline, bipy = 2,2'-bipyridine, 5,5'-me_2bipy = 5,5'-dimethyl-2,2'-bipy) in methyl alcohol, in the presnece of triethylamine, leads to the formation of hexameric [V_2~(IV)V_4~V] oxo-alkoxo-vanadates of the general formula [V_6O_12(mu_2-OCH_3)_4(L)_4]·xH_2O [L = phen (1·4H_2O), 5-mephen (2·6H_2O), bipy (3·4H_2O), 5,5'-me_2bipy (4·H_2O)]. X-ray structure analysis of 1·2H_2O and 4·8CH_3OH revealed a pair of V_3O_13N_4 trimeric units sharing two corners, with a centrosymmetric planar V_6-core. In addition, a fully oxidized V~V species [V_4~VO_8(OCH_3)_2(mu_3-OCH_3)_2(5,5'-me_2bipy)_2]·3CH_3OH (5·3CH_3OH) was isolated from the reaction mixture used for the synthesis of 4·H_2O. The crystal structure of 5·3CH_3OH revealed a dicubane-like framework with two missing vertices. Electron paramagnetic resonance (EPR) and variable temperature magnetic susceptibility studies for the hexamers 1·4H_2O and 3·4H_2O showed the complete localization of the single 3d electrons on the V~(IV) ions and unusual ferromagnetic interaction between the two paramagnetic vanadium(IV) ions separated by a distance of about 5.1 A. Furthermore, intermolecular antiferromagnetic interactions through pi-contacts of phenyl rings were observed for these species below 8 K. The ferromagnetic exchange coupling observed in the hexanuclear coupling observed in the hexanuclear compounds 1·4H_2O and 3·4H_2O is also discussed using ab initio UHF calculations on a model compound. The value of the exchange coupling constant (3.7 cm~(-1)) for this model compound, calculated using the broken symmetry approach, is in good agreement, both in sign and magnitude, with the experimental J values (6.00 cm~(-1) for 1·4H_2O and 8.54 cm~(-1) for 3·4H_2O).
机译：[V〜（VI）OCl_2（thf）_2]与二齿氮供体配体的反应（L：phen = 1,10-菲咯啉，5-mephen = 5-甲基-1,10-菲咯啉，bipy = 2，在三乙胺的存在下，在甲醇中的2'-联吡啶，5,5'-me_2bipy = 5,5'-二甲基-2,2'-bipy导致六聚体[V_2〜（IV）V_4〜 V]通式为[V_6O_12（mu_2-OCH_3）_4（L）_4]·xH_2O的含氧-烷氧基钒酸盐[L = phen（1·4H_2O），5-mephen（2·6H_2O），bipy（3·4H_2O ），5,5'-me_2bipy（4·H_2O）]。对1·2H_2O和4·8CH_3OH的X射线结构分析显示，一对V_3O_13N_4三聚体单元共享两个角，且具有中心对称的平面V_6-核。此外，从用于反应的反应混合物中分离出完全氧化的V〜V物质[V_4〜VO_8（OCH_3）_2（mu_3-OCH_3）_2（5,5'-me_2bipy）_2]·3CH_3OH（5·3CH_3OH）。合成4·H_2O。 5·3CH_3OH的晶体结构显示出具有两个缺失顶点的类似二氢呋喃的骨架。六聚体1·4H_2O和3·4H_2O的电子顺磁共振（EPR）和可变温度磁化率研究表明，单个3d电子在V〜（IV）离子上完全定位，并且两个顺磁性钒（IV）之间存在异常的铁磁相互作用）离子相距约5.1A。此外，对于低于8 K的这些物种，通过苯环的pi接触观察到分子间反铁磁相互作用。在六核化合物1·4H_2O和还使用从头开始的UHF计算对模型化合物进行了3·4H_2O的讨论。使用破坏对称方法计算的该模型化合物的交换耦合常数（3.7 cm〜（-1））的值和幅度与实验J值（6.00 cm〜（- 1）对于1·4H_2O和8.54 cm〜（-1）对于3·4H_2O）。

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