title: Solid-state EPR strategies for the structural characterization of paramagnetic NO adducts of frustrated Lewis pairs (FLPs).
abstract: Anisotropic interactions present in three new nitroxide radicals prepared by N,N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs) have been characterized by continuous-wave (cw) and pulsed X-band EPR spectroscopies in solid FLP-hydroxylamine matrices at 100 K. Anisotropic g-tensor values and (11)B, (14)N, and (31)P hyperfine coupling tensor components have been extracted from continuous-wave lineshape analyses, electron spin echo envelope modulation (ESEEM), and hyperfine sublevel correlation spectroscopy (HYSCORE) experiments with the help of computer simulation techniques. Suitable fitting constraints are developed on the basis of density functional theory (DFT) calculations. These calculations reveal that different from the situation in standard nitroxide radicals (TEMPO), the g-tensors are non-coincident with any of the nuclear hyperfine interaction tensors. The determination of these interaction parameters turns out to be successful, as the cw- and pulse EPR experiments are highly complementary in informational content. While the continuous-wave lineshape is largely influenced by the anisotropic hyperfine coupling to (14)N and (31)P, the ESEEM and HYSCORE spectra contain important information about the (11)B hyperfine coupling and nuclear electric quadrupolar interaction. The set of cw- and pulsed EPR experiments, with fitting constraints developed by DFT calculations, defines an efficient strategy for the structural analysis of paramagnetic FLP adducts.
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, P.O. Box 369, 13560-970 São Carlos, São Paulo, Brazil.
authors.forename: Marcos
authors.initials: M
authors.lastname: de Oliveira
authors.affiliation: Laboratorium für Physikalische Chemie, ETH Zürich, Vladimir-Prelog-Weg 2, 8049 Zürich, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wiegand
authors.affiliation: Organisch-Chemisches Institut, WWU Münster, Corrensstraße 40, D 48149 Münster, Germany.
authors.forename: Lisa-Maria
authors.initials: LM
authors.lastname: Elmer
authors.affiliation: Organisch-Chemisches Institut, WWU Münster, Corrensstraße 40, D 48149 Münster, Germany.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Sajid
authors.affiliation: Organisch-Chemisches Institut, WWU Münster, Corrensstraße 40, D 48149 Münster, Germany.
authors.forename: Gerald
authors.initials: G
authors.lastname: Kehr
authors.affiliation: Organisch-Chemisches Institut, WWU Münster, Corrensstraße 40, D 48149 Münster, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Erker
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, P.O. Box 369, 13560-970 São Carlos, São Paulo, Brazil.
authors.forename: Claudio José
authors.initials: CJ
authors.lastname: Magon
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, P.O. Box 369, 13560-970 São Carlos, São Paulo, Brazil.
authors.forename: Hellmut
authors.initials: H
authors.lastname: Eckert