Nearest- and Next-Nearest-Neighbor Ru(II)/Ru(III) Electronic Coupling in Cyanide-Bridged Tetra-Ruthenium Square Complexes.

详细信息    查看全文

• 作者：Ju-Ling Lin ; Chia-Nung Tsai ; Sheng-Yi Huang ; John F. Endicott ; Yuan-Jang Chen ; Hsing-Yin Chen
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：September 5, 2011
• 年：2011
• 卷：50
• 期：17
• 页码：8274-8280
• 全文大小：895K
• 年卷期：v.50,no.17(September 5, 2011)
• ISSN：1520-510X

文摘

Electrochemical properties of cyanide-bridged metal squares, [Ru₄]⁴⁺ and [Rh₂鈥揜u₂]⁶⁺, clearly demonstrate the role of the nearest (NN) metal moiety in mediating the next-nearest neighbor (NNN) metal-to-metal electronic coupling. The differences in electrochemical potentials for successive oxidations of equivalent Ru(II) centers in [Ru₄]⁴⁺ are 螖E_1/2 = 217 mV and 256 mV and are related to intense, dual metal-to-metal-charge-transfer (MMCT) absorption bands. This contrasts with a small value of 螖E_1/2 = 77 mV and no MMCT absorption bands observed to accompany the oxidations of [Rh₂鈥揜u₂]⁶⁺. These observations demonstrate NN-mediated superexchange mixing by the linker Ru of NNN Ru(II) and Ru(III) moieties and that this mixing results in a NNN contribution to the ground state stabilization energy of about 90 卤 20 meV. In contrast, the classical Hush model for mixed valence complexes with the observed MMCT absorption parameters predicts a NNN stabilization energy of about 6 meV. The observations also indicate that the amount of charge delocalization per Ru(II)/Ru(III) pair is about 4 times greater for the NN than the NNN couples in these CN-bridged complexes, which is consistent with DFT modeling. A simple fourth-order secular determinant model is used to describe the effects of donor/acceptor mixing in these complexes.