Eisenhart Reed J, Rudd P Alex, Planas Nora, Boyce David W, Carlson Rebecca K, Tolman William B, Bill Eckhard, Gagliardi Laura, Lu Connie C
∥Max Planck Institut für Chemische Energiekonversion (MPI-CEC), Stiftstraße 34-36, 45470 Mülheim an der Ruhr, Germany.
Inorg Chem. 2015 Aug 3;54(15):7579-92. doi: 10.1021/acs.inorgchem.5b01163. Epub 2015 Jul 13.
Into the metalloligand Cr[N(o-(NCH2P((i)Pr)2)C6H4)3] (1, CrL) was inserted a second chromium atom to generate the dichromium complex Cr2L (2), which is a homobimetallic analogue of the known MCrL complexes, where M is manganese (3) or iron (4). The cationic and anionic counterparts, MCrL and MCrL, respectively, were targeted, and each MCr pair was isolated in at least one other redox state. The solid-state structures of the MCrL redox members are essentially the same, with ultrashort metal-metal bonds between 1.96 and 1.74 Å. The formal shortness ratios (r) of these interactions are between 0.84 and 0.74 and are interpreted as triple to quintuple metal-metal bonds with the aid of theory. The trio of (d-d)(10) species Cr2L (2(red)), MnCrL (3), and FeCrL (4(ox)) are S = 0 diamagnets. On the basis of M-Cr bond distances and theoretical calculations, the strength of the metal-metal bond across the (d-d)(10) series increases in the order Fe < Mn < Cr. The methylene protons in the ligand are shifted downfield in the (1)H NMR spectra, and the diamagnetic anisotropy of the metal-metal bond was calculated as -3500 × 10(-36), -3900 × 10(-36), and -5800 × 10(-36) m(3) molecule(-1) for 2(red), 3, and 4(ox) respectively. The magnitude of diamagnetic anisotropy is, thus, affected more by bond polarity than by bond order. A comparative vis-NIR study of quintuply bonded 2(red) and 3 revealed a large red shift in the δ(4) → δ(3)δ* transition energy upon swapping from the (Cr2)(2+) to the (MnCr)(3+) core. Complex 2(red) was further investigated by resonance Raman spectroscopy, and a band at 434 cm(-1) was assigned as the Cr-Cr bond vibration. Finally, 4(ox) exhibited a Mössbauer doublet with an isomer shift of 0.18 mm/s that suggests a primarily Fe-based oxidation to Fe(I).
在金属配体Cr[N(o-(NCH2P((i)Pr)2)C6H4)3]（1，CrL）中插入第二个铬原子，生成二铬配合物Cr2L（2），它是已知的MCrL配合物（其中M为锰（3）或铁（4））的同双核类似物。分别针对阳离子和阴离子对应物MCrL和MCrL，并且每个MCr对都以至少一种其他氧化态被分离出来。MCrL氧化还原成员的固态结构基本相同，金属 - 金属键超短，键长在1.96至1.74 Å之间。这些相互作用的形式短程比（r）在0.84至0.74之间，并借助理论解释为三重至五重金属 - 金属键。(d-d)(10)物种Cr2L（2(red)）、MnCrL（3）和FeCrL（4(ox)）这三种物质都是S = 0的抗磁体。基于M - Cr键距离和理论计算，(d-d)(10)系列中金属 - 金属键的强度按Fe < Mn < Cr的顺序增加。配体中的亚甲基质子在(1)H NMR光谱中向低场移动，并且对于2(red)、3和4(ox)，金属 - 金属键的抗磁各向异性分别计算为-3500×10(-36)、-3900×10(-36)和-5800×10(-36) m(3) molecule(-1)。因此，抗磁各向异性的大小受键极性的影响比受键级的影响更大。对五重键合的2(red)和3进行的比较可见 - 近红外研究表明，从(Cr2)(2+)核心交换到(MnCr)(3+)核心时，δ(4) → δ(3)δ*跃迁能量发生了很大的红移。通过共振拉曼光谱对配合物2(red)进行了进一步研究，434 cm(-1)处的一条谱带被指定为Cr - Cr键振动。最后，4(ox)表现出一个穆斯堡尔双峰，其同质异能位移为0.18 mm/s，这表明主要是基于铁的氧化为Fe(I)。
