Control of Exchange Interactions in [pi] Dimers of 6-Oxophenalenoxyl Neutral [pi] Radicals: Spin-Density Distributions and Multicentered-Two-Electron Bonding Governed by Topological Symmetry and Substitution atthe8-Position

• Published in: Chemistry : a European journal Vol. 19; no. 36; p. 11904
• Main Authors: Nishida, Shinsuke, Kawai, Junya, Moriguchi, Miki, Ohba, Tomohiro, Haneda, Naoki, Fukui, Kozo, Fuyuhiro, Akira, Shiomi, Daisuke, Sato, Kazunobu, Takui, Takeji, Nakasuji, Kazuhiro, Morita, Yasushi
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 02.09.2013
• Subjects: Crystal structure
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201301783

The tri-tert-butylphenalenyl (TBPLY) radical exists as a π dimer in the crystal form with perfect overlapping of the singly occupied molecular orbitals (SOMOs) causing strong antiferromagnetic exchange interactions. 2,5-Di-tert-butyl-6-oxophenalenoxyl (6OPO) is a phenalenyl-based air-stable neutral π radical with extensive spin delocalization and is a counter analogue of phenalenyl in terms of the topological symmetry of the spin density distribution. X-ray crystal structure analyses showed that 8-tert-butyl- and 8-(p-XC6H4)-6OPOs (X=I, Br) also form π dimers in the crystalline state. The π-dimeric structure of 8-tert-butyl-6OPO is seemingly similar to that of TBPLY even though its SOMO-SOMO overlap is small compared with that of TBPLY. The 8-(p-XC6H4) derivatives form slipped stacking π dimers in which the SOMO-SOMO overlaps are greater than in 8-tert-butyl-6OPO, but still smaller than in TBPLY. The solid-state electronic spectra of the 6OPO derivatives show much weaker intradimer charge-transfer bands, and SQUID measurements for 8-(p-BrC6H4)-6OPO show a weak antiferromagnetic exchange interaction in the π dimer. These results demonstrate that the control of the spin distribution patterns of the phenalenyl skeleton switches the mode of exchange interaction within the phenalenyl-based π dimer. The formation of the relevant multicenter-two-electron bonds is discussed. [PUBLICATION ABSTRACT]