Electronic and magnetic metal–metal interactions in dinuclear oxomolybdenum(V) complexes across bis-phenolate bridging ligands with different spacers between the phenolate termini: ligand-centred vs. metal-centred redox activity
Electronic and magnetic metal–metal interactions in dinuclear oxomolybdenum(V) complexes across bis-phenolate bridging ligands with different spacers between the phenolate termini: ligand-centred vs. metal-centred redox activity
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双核氧代钼 (V) 配合物跨双酚盐桥接配体（酚盐末端之间具有不同间隔基）的电子和磁性金属-金属相互作用：以配体为中心与以金属为中心的氧化还原活性
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发表时间：
2001
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通讯作者：
C. Screttas
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作者：
S. Bayly;Elizabeth R. Humphrey;Cecilia G. Paredes;Zöe R. Bell;J. Jeffery;J. McCleverty;M. Ward;F. Totti;D. Gatteschi;S. Courric;B. R. Steele;C. Screttas
制备了一系列双核配合物，其中两个 {MoV(TpMe,Me)(O)Cl} 片段（缩写为 Mo；TpMe,Me = 三(3,5-二甲基吡唑-1-基)硼氢化物）连接到双对酚桥配体 [(4,4'-OC6H4)–X–(4,4'-C6H4O)]2− 的任一端。配合物为 Mo2(CC) (X = CHCH)、Mo2(CC)2 (X = CHCH–CHCH)、Mo2(CC)3 (X = CHCH–CHCH–CHCH)、Mo2(th) (X = 2,5-噻吩二基)、Mo2(th)2 (X = 2,5:2′,5′-联噻吩二基)、Mo2(th)3 (X = 2,5:2′,5′:2″,5″-三噻吩二基)、Mo2(CC) (X = CC)、Mo2(NN) (X = NN)、Mo2(CO) [X = C(O)] 和 Mo2(C2ΦC2) [X = CHCH(1,4-C6H4)CHCH]。为了了解不同的间隔基团 X 如何有效地介导两个氧化还原活性顺磁性 Mo 中心之间的电子和磁性相互作用，我们进行了电化学、UV/VIS/NIR 光谱电化学和磁性测量。电子相互作用是通过两个连续的单电子氧化之间的氧化还原分离来确定的，这两个单电子氧化形式上是Mo(VI)-Mo(V)对；研究发现，桥连配体中的噻吩基单元在维持长距离电子通信方面比相当长度的对亚苯基或乙烯基间隔基更有效。偶氮（NN）键提供比乙烯基或乙炔基间隔基弱得多的电子相互作用。 UV/VIS/NIR光谱电化学研究表明，虽然第一次氧化以金属为中心，产生在近红外区域具有特征性强酚盐→Mo(VI) LMCT跃迁的Mo(VI)–Mo(V)物种，但双重氧化络合物的光谱具有醌的特征：因此，氧化时形成的物种序列为[Mo(V)(μ-二醇)Mo(V)]0
→ [Mo(V)(μ-二醇)Mo(VI)]+ → [Mo(V)(μ-醌)Mo(V)]2+，具有与第二次氧化相关的内部电荷重新分布。半经验ZINDO计算对此提供了一些支持。 Mo2(CC)、Mo2(th)、Mo2(NN)和Mo2(CC)的磁化率测量表明，正如基于自旋极化图所预期的那样，它们都是弱反铁磁耦合的，磁相互作用的强度顺序与电子耦合的顺序相反，使得Mo2(th)提供最强的电子相互作用，但提供最弱的磁相互作用。
A series of dinuclear complexes has been prepared in which two {MoV(TpMe,Me)(O)Cl} fragments (abbreviated as Mo; TpMe,Me = tris(3,5-dimethylpyrazol-1-yl)hydroborate) are attached to either end of a bis-p-phenolate bridging ligand [(4,4′-OC6H4)–X–(4,4′-C6H4O)]2−. The complexes are Mo2(CC) (X = CHCH), Mo2(CC)2 (X = CHCH–CHCH), Mo2(CC)3 (X = CHCH–CHCH–CHCH), Mo2(th) (X = 2,5-thiophenediyl), Mo2(th)2 (X = 2,5:2′,5′-bithiophenediyl), Mo2(th)3 (X = 2,5:2′,5′:2″,5″-terthiophenediyl), Mo2(CC) (X = CC), Mo2(NN) (X = NN), Mo2(CO) [X = C(O)] and Mo2(C2ΦC2) [X = CHCH(1,4-C6H4)CHCH]. Electrochemical, UV/VIS/NIR spectroelectrochemical and magnetic measurements have been carried out in order to see how effectively the different spacer groups X mediate electronic and magnetic interactions between the two redox-active, paramagnetic, Mo centres. The electronic interactions were determined from the redox separation between the two successive one-electron oxidations which are formally Mo(VI)–Mo(V) couples; it was found that thienyl units in the bridging ligand are much more effective at maintaining electronic communication over long distances than p-phenylene or ethenyl spacers of comparable lengths. The azo (NN) linkage afforded a much weaker electronic interaction than the ethenyl or ethynyl spacers. UV/VIS/NIR spectroelectrochemical studies showed that whereas the first oxidation is metal-centred to give Mo(VI)–Mo(V) species with characteristic intense phenolate→Mo(VI) LMCT transitions in the near-IR region, the spectra of the doubly oxidised complexes are characteristic of quinones: thus, the sequence of species formed on oxidation is [Mo(V)(μ-diolate)Mo(V)]0
→ [Mo(V)(μ-diolate)Mo(VI)]+ → [Mo(V)(μ-quinone)Mo(V)]2+, with an internal charge redistribution associated with the second oxidation. Semi-empirical ZINDO calculations provide some support for this. Magnetic susceptibility measurements on Mo2(CC), Mo2(th), Mo2(NN) and Mo2(CC) show that all are weakly antiferromagnetically coupled, as expected on the basis of a spin-polarisation picture, with the order of strength of the magnetic interaction being the reverse of the order for electronic coupling, such that Mo2(th) affords the strongest electronic interaction but the weakest magnetic interaction.