Electron Spin-Spin Exchange Coupling Mediated by the Porphyrin System
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- 作者：David A. Shultz ; Christopher P. Mussari ; Krishna Kumar Ramanathan ; and Jeff W. Kampf
- 刊名：Inorganic Chemistry
- 出版年：2006
- 出版时间：July 24, 2006
- 年：2006
- 卷：45
- 期：15
- 页码：5752 - 5759
- 全文大小：190K
- 年卷期：v.45,no.15(July 24, 2006)
- ISSN：1520-510X
文摘
The syntheses and electron paramagnetic resonance (EPR) spectral characterizations of porphyrins (1-3) substitutedwith two radical groups bound to trans-meso positions are described. One of these compounds, 3, has beenstudied by variable-temperature magnetic susceptibility and has been structurally characterized. Biradical porphyrin3 is monoclinic, space group P21/n, with a = 12.239(2) Å, b = 17.819(3) Å, c = 34.445(7) Å, 
= 90
, 
=97.466(3), 
= 90, and Z = 2. The bis(nitroxide) porphyrins 1 and 2 exhibit fluid solution EPR spectra consistentwith 
J 
a. No evidence was observed for conformational modulation of J by rotation about single bonds asshown by the lack of change of the EPR spectra as a function of temperature. The bis(semiquinone) porphyrin 3exhibits frozen-solution EPR spectra with zero-field splitting and a 
ms = 2 transition characteristic of a tripletstate. The intensity of the ms = 2 transition of 3 was measured as a function of temperature, and the data fitaccording to a singlet-triplet model to yield J(3,solution) = -75 cm-1 (H = - 2J
1·2). Polycrystalline samplesof porphryin 3 were examined by variable-temperature magnetometry. The paramagnetic susceptibility data werefit using a modified Bleaney-Bowers equation to give J(3,solid) = -29 cm-1 (H = - 2J1·2). The antiferromagneticJ values are consistent with the 
topology of the porphyrin ring.
= 90, =97.466(3), = 90, and Z = 2. The bis(nitroxide) porphyrins 1 and 2 exhibit fluid solution EPR spectra consistentwith J a. No evidence was observed for conformational modulation of J by rotation about single bonds asshown by the lack of change of the EPR spectra as a function of temperature. The bis(semiquinone) porphyrin 3exhibits frozen-solution EPR spectra with zero-field splitting and a ms = 2 transition characteristic of a tripletstate. The intensity of the ms = 2 transition of 3 was measured as a function of temperature, and the data fitaccording to a singlet-triplet model to yield J(3,solution) = -75 cm-1 (H = - 2J1·2). Polycrystalline samplesof porphryin 3 were examined by variable-temperature magnetometry. The paramagnetic susceptibility data werefit using a modified Bleaney-Bowers equation to give J(3,solid) = -29 cm-1 (H = - 2J1·2). The antiferromagneticJ values are consistent with the topology of the porphyrin ring.