How Do Nitriles Compare with Isoelectronic Alkynyl Groups in the Electronic Communication between Iron Centers Bridged by Phenylenebis- and -tris(nitrile) Ligands? An Electronic and Crystal-Structure

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• 作者：Laure虂line Bonniard ; Samia Kahlal ; Abdou K. Diallo ; Ca虂tia Ornelas ; Thierry Roisnel ; Gabriele Manca ; Joa虄o Rodrigues ; Jaime Ruiz ; Didier Astruc ; Jean-Yves Saillard
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：January 3, 2011
• 年：2011
• 卷：50
• 期：1
• 页码：114-124
• 全文大小：1082K
• 年卷期：v.50,no.1(January 3, 2011)
• ISSN：1520-510X

文摘

Density functional theory (DFT) calculations on the model [{FeCp(dpe)}₂{1,4-C₆H₄(CN)₂}]²⁺ (3²⁺; dpe = diphosphinoethane) of salts of the cations [{FeCp(dppe)}₂{1,4-C₆H₄(CN)₂}]²⁺ (1²⁺; dppe = 1,2-bis[diphenyldiphosphino]ethane) and [{FeCp*(CO)₂}₂{1,4-C₆H₄(CN)₂}]²⁺ (2²⁺), for which the X-ray crystal structures have been determined, as well as on its isomer [{FeCp(dpe)}₂{1,3-C₆H₄(CN)₂}]²⁺ (4²⁺) and on the related complex [{FeCp(dpe)}₃{1,3,5-C₆H₃(CN)₃}]³⁺ (5²⁺), indicate that the highest occupied molecular orbitals (HOMOs) of these compounds are localized on the metal centers with negligible participation of the C₆ ring. Thus, the poly(nitrile)phenylene ligand efficiently quenches the electronic communication between the metal centers. This is at variance with the related isoelectronic polyacetylene phenylene complexes, in which the iron centers have been shown to be electronically coupled. Consistently, apart from the case of 3³⁺, which shows some degree of delocalization, all of the oxidized forms of 3²⁺, 4²⁺, and 5²⁺ can be described as class II, localized mixed-valent species, in agreement with the electrochemical data showing two close oxidation potentials around 1 V vs FeCp*₂. This is at variance with the p-phenylene-briged biethynyldiiron analogue, for which extended electronic delocalization was earlier shown to provide greater degree of delocalization of the mixed valency. Time-dependent DFT calculations on 3²⁺, 4²⁺, and 5²⁺ indicate that the lowest-energy absorption band is associated with metal-to-ligand charge-transfer transitions involving the metallic HOMOs and the two lowest unoccupied molecular orbitals that derive from the lowest 蟺*(phenylene) orbitals with some 蟺*(CN) bonding admixture.