Aminoxyl Radicals of B/P Frustrated Lewis Pairs: Refinement of the Spin-Hamiltonian Parameters by Field- and Temperature-Dependent Pulsed EPR Spectroscopy

Autor(es)

de Oliveira, Jr., Marcos ^[1] ; Knitsch, Robert ^[2] ; Sajid, Muhammad ^[3] ; Stute, Annika ^[3] ; Elmer, Lisa-Maria ^[3] ; Kehr, Gerald ^[3] ; Erker, Gerhard ^[3] ; Magon, Claudio J. ^[1] ; Jeschke, Gunnar ^[4] ; Eckert, Hellmut ^{[1, 2]}

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Fis Sao Carlos, POB 369, BR-13560970 Sao Carlos, SP - Brazil

^[2] WWU Munster, Inst Phys Chem, Corrensstr 30, D-48149 Munster - Germany

^[3] WWU Munster, Inst Organ Chem, Corrensstr 30, D-48149 Munster - Germany

^[4] ETH, Phys Chem Lab, Vladimir Prelog Weg 2, CH-8049 Zurich - Switzerland

• Tipo de documento: Artigo Científico
• Fonte: PLoS One; v. 11, n. 6 JUN 23 2016.
• Citações Web of Science: 4

Resumo

Q-band and X-band pulsed electron paramagnetic resonance spectroscopic methods (EPR) in the solid state were employed to refine the parameters characterizing the anisotropic interactions present in six nitroxide radicals prepared by N, N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs). The EPR spectra are characterized by the g-anisotropy as well as by nuclear hyperfine coupling between the unpaired electron and the B-11/B-10, N-14 and P-31 nuclear magnetic moments. It was previously shown that continuous-wave spectra measured at X-band frequency (9.5 GHz) are dominated by the magnetic hyperfine coupling to N-14 and P-31, whereas the g-tensor values and the B-11 hyperfine coupling parameters cannot be refined with high precision from lineshape fitting. On the other hand, the X-band electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) spectra are completely dominated by the nuclear hyperfine coupling to the B-11 nuclei, allowing a selective determination of their interaction parameters. In the present work this analysis has been further validated by temperature dependent ESEEM measurements. In addition, pulsed EPR data measured in the Q-band (34 GHz) are reported, which present an entirely different situation: the g-tensor components can be measured with much higher precision, and the ESEEM and HYSCORE spectra contain information about all of the B-10, B-11, N-14 and P-31 hyperfine interaction parameters. Based on these new results, we report here high-accuracy and precision data of the EPR spin Hamiltonian parameters measured on six FLP-NO radical species embedded in their corresponding hydroxylamine host structures. While the ESEEM spectra at Q-band frequency turn out to be very complex (due to the multinuclear contribution to the overall signal) in the HYSCORE experiment the extension over two dimensions renders a better discrimination between the different nuclear species, and the signals arising from hyperfine coupling to B-10, B-11, N-14 and P-31 nuclei can be individually analyzed. (AU)

• Processo FAPESP: 13/23490-3 - Técnicas de ressonância magnética empregadas no estudo da correlação estrutura/propriedades em vidros e vitrocerâmicas fotônicos
• Beneficiário: Marcos de Oliveira Junior
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 13/07793-6 - CEPIV - Centro de Ensino, Pesquisa e Inovação em Vidros
• Beneficiário: Edgar Dutra Zanotto
• Modalidade de apoio: Auxílio à Pesquisa - Centros de Pesquisa, Inovação e Difusão - CEPIDs
• Processo FAPESP: 15/04063-2 - Ambientes de coordenação de íons terra-rara em vidros fotônicos analisados por técnicas de ressonância paramagnética eletrônica pulsada
• Beneficiário: Marcos de Oliveira Junior
• Modalidade de apoio: Bolsas no Exterior - Estágio de Pesquisa - Pós-Doutorado