Control of Exchange Interactions in π Dimers of 6-Oxophenalenoxyl Neutral π Radicals: Spin-Density Distributions and Multicentered-Two-Electron Bonding Governed by Topological Symmetry and Substitution at the 8-Position.
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.
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan), Fax: (+81) 6-6850-5395; Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 5 Sanban-cho, Chiyoda-ku, Tokyo 102-0075 (Japan).
Shinsuke
S
Nishida
Junya
J
Kawai
Miki
M
Moriguchi
Tomohiro
T
Ohba
Naoki
N
Haneda
Kozo
K
Fukui
Akira
A
Fuyuhiro
Daisuke
D
Shiomi
Kazunobu
K
Sato
Takeji
T
Takui
Kazuhiro
K
Nakasuji
Yasushi
Y
Morita
X‐ray diffraction; absorption; density functional calculations; magnetic properties; radicals