Determining the Conformational Landscape of 蟽 and 蟺 Coupling Using para-Phenylene and 鈥淎viram鈥揜atner鈥?Bridges

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• 作者：Daniel E. Stasiw ; Jinyuan Zhang ; Guangbin Wang ; Ranjana Dangi ; Benjamin W. Stein ; David A. Shultz ; Martin L. Kirk ; Lukasz Wojtas ; Roger D. Sommer
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：July 29, 2015
• 年：2015
• 卷：137
• 期：29
• 页码：9222-9225
• 全文大小：347K
• ISSN：1520-5126

文摘

The torsional dependence of donor鈥揵ridge鈥揳cceptor (D鈥揃鈥揂) electronic coupling matrix elements (H_DA, determined from the magnetic exchange coupling, J) involving a spin S_D = 1/2 metal semiquinone (Zn-SQ) donor and a spin S_A = 1/2 nitronylnitroxide (NN) acceptor mediated by the 蟽/蟺-systems of para-phenylene and methyl-substituted para-phenylene bridges and by the 蟽-system of a bicyclo[2.2.2]octane (BCO) bridge are presented and discussed. The positions of methyl group(s) on the phenylene bridge allow for an experimentally determined evaluation of conformationally dependent (蟺) and conformationally independent (蟽) contributions to the electronic and magnetic exchange couplings in these D鈥揃鈥揂 biradicals at parity of D and A. The trend in the experimental magnetic exchange couplings are well described by CASSCF calculations. The torsional dependence of the pairwise exchange interactions are further illuminated in three-dimensional, 鈥淩amachandran-type鈥?plots that relate D鈥揃 and B鈥揂 torsions to both electronic and exchange couplings. Analysis of the magnetic data shows large variations in magnetic exchange (J 鈮?1鈥?75 cm^鈥?) and electronic coupling (H_DA 鈮?450鈥?000 cm^鈥?) as a function of bridge conformation relative to the donor and acceptor. This has allowed for an experimental determination of both the 蟽- and 蟺-orbital contributions to the exchange and electronic couplings.