Liu Isiah Po-Chun, Bénard Marc, Hasanov Hasan, Chen I-Wen Peter, Tseng Wei-Hsiang, Fu Ming-Dung, Rohmer Marie-Madeleine, Chen Chun-hsien, Lee Gene-Hsiang, Peng Shie-Ming
Department of Chemistry, National Taiwan University, 1, Roosevelt Rd., Sec. 4, Taipei 106, Taiwan.
Chemistry. 2007;13(31):8667-77. doi: 10.1002/chem.200700750.
Two new linear pentanickel complexes [Ni5(bna)4(Cl)2][PF6]2 (1) and [Ni5(bna)4(Cl)2][PF6]4 (2; bna=binaphthyridylamide), were synthesized and structurally characterized. A derivative of 1, [Ni5(bna)4(NCS)2][NCS]2 (3), was also isolated for the purpose of the conductance experiments carried out in comparison with [Ni5(tpda)4(NCS)2] (4; tpda=tripyridyldiamide). The metal framework of complex 2 is a standard [Ni5]10+ core, isoelectronic with that of [Ni5(tpda)4Cl2] (5). Also as in 5, complex 2 has an antiferromagnetic ground state (J=-15.86 cm(-1)) resulting from a coupling between the terminal nickel atoms, both in high-spin sate (S=1). Complex 1 displays the first characterized linear nickel framework in which the usual sequence of NiII atoms has been reduced by two electrons. Each dinickel unit attached to the naphthyridyl moieties is assumed to undergo a one-electron reduction, whereas the central nickel formally remains NiII. DFT calculations suggest that the metal framework of the mixed-valence complex 1 should be described as intermediate between a localized picture corresponding to NiII-NiI-NiII-NiI-NiII and a fully delocalized model represented as (Ni2)3+-NiII-(Ni2)3+. Assuming the latter model, the ground state of 1 results from an antiferromagnetic coupling (J=-34.03 cm(-1)) between the two (Ni2)3+ fragments, considered each as a single magnetic centre (S=3/2). An intervalence charge-transfer band is observed in the NIR spectrum of 1 at 1186 nm, suggesting, in accordance with DFT calculations, that 1 should be assigned to Robin-Day class II of mixed-valent complexes. Scanning tunnelling microscopy (STM) methodology was used to assess the conductance of single molecules of 3 and 4. Compound 3 was found approximately 40% more conductive than 4, a result that could be assigned to the electron mobility induced by mixed-valency in the naphthyridyl fragments.
合成并表征了两种新型线性五镍配合物[Ni5(bna)4(Cl)2][PF6]2 (1)和[Ni5(bna)4(Cl)2][PF6]4 (2；bna = 联萘啶酰胺)。还分离出了1的衍生物[Ni5(bna)4(NCS)2][NCS]2 (3)，用于与[Ni5(tpda)4(NCS)2] (4；tpda = 三吡啶二酰胺)进行对比的电导实验。配合物2的金属骨架是标准的[Ni5]10+核，与[Ni5(tpda)4Cl2] (5)的等电子体。与5一样，配合物2由于末端镍原子之间的耦合而具有反铁磁基态(J = -15.86 cm(-1))，两者均处于高自旋态(S = 1)。配合物1展示了首个经表征的线性镍骨架，其中常见的NiII原子序列减少了两个电子。假定连接到萘啶基部分的每个二镍单元经历单电子还原，而中心镍形式上仍为NiII。密度泛函理论计算表明，混合价配合物1的金属骨架应描述为介于对应于NiII-NiI-NiII-NiI-NiII的局域图像和表示为(Ni2)3+-NiII-(Ni2)3+的完全离域模型之间。假定为后一种模型，1的基态源于两个(Ni2)3+片段之间的反铁磁耦合(J = -34.03 cm(-1))，每个片段视为一个单一磁中心(S = 3/2)。在1的近红外光谱中于1186 nm处观察到一个价间电荷转移带，这表明根据密度泛函理论计算，1应归为罗宾-戴II类混合价配合物。使用扫描隧道显微镜(STM)方法评估了3和4单分子的电导。发现化合物3的导电性比4高约40%，该结果可归因于萘啶基片段中混合价诱导的电子迁移率。
