Shultz David A, Mussari Christopher P, Ramanathan Krishna Kumar, Kampf Jeff W
Department of Chemistry, North Carolina State University, Raleigh, NC 27695-8204, USA.
Inorg Chem. 2006 Jul 24;45(15):5752-9. doi: 10.1021/ic060209z.
The syntheses and electron paramagnetic resonance (EPR) spectral characterizations of porphyrins (1-3) substituted with two radical groups bound to trans-meso positions are described. One of these compounds, 3, has been studied by variable-temperature magnetic susceptibility and has been structurally characterized. Biradical porphyrin 3 is monoclinic, space group P2(1)/n, with a = 12.239(2) A, b = 17.819(3) A, c = 34.445(7) A, alpha = 90 degrees , beta = 97.466(3) degrees , gamma = 90 degrees , and Z = 2. The bis(nitroxide) porphyrins 1 and 2 exhibit fluid solution EPR spectra consistent with |J| >> |a|. No evidence was observed for conformational modulation of J by rotation about single bonds as shown by the lack of change of the EPR spectra as a function of temperature. The bis(semiquinone) porphyrin 3 exhibits frozen-solution EPR spectra with zero-field splitting and a Deltam(s) = 2 transition characteristic of a triplet state. The intensity of the Deltam(s) = 2 transition of 3 was measured as a function of temperature, and the data fit according to a singlet-triplet model to yield J(3,solution) = -75 cm(-1) (H = - 2Jŝ1.ŝ2). Polycrystalline samples of porphryin 3 were examined by variable-temperature magnetometry. The paramagnetic susceptibility data were fit using a modified Bleaney-Bowers equation to give J(3,solid) = -29 cm(-1) (H = - 2Jŝ(1).ŝ(2)). The antiferromagnetic J values are consistent with the pi topology of the porphyrin ring.
本文描述了在反式中位位置连接有两个自由基基团的卟啉（1 - 3）的合成及其电子顺磁共振（EPR）光谱表征。其中一种化合物3，已通过变温磁化率进行了研究，并进行了结构表征。双自由基卟啉3为单斜晶系，空间群P2(1)/n，a = 12.239(2) Å，b = 17.819(3) Å，c = 34.445(7) Å，α = 90°，β = 97.466(3)°，γ = 90°，Z = 2。双（氮氧化物）卟啉1和2在流体溶液中的EPR光谱表明|J| >> |a|。未观察到通过单键旋转对J进行构象调制的证据，这表现为EPR光谱随温度变化而无变化。双（半醌）卟啉3在冷冻溶液中的EPR光谱具有零场分裂和三重态特征的Δm(s) = 2跃迁。测量了3的Δm(s) = 2跃迁强度随温度的变化，数据根据单重态 - 三重态模型拟合，得到J(3,溶液) = -75 cm(-1)（H = - 2Jŝ1.ŝ2）。通过变温磁强计对卟啉3的多晶样品进行了检测。顺磁磁化率数据使用修正的Bleaney - Bowers方程拟合，得到J(3,固体) = -29 cm(-1)（H = - 2Jŝ(1).ŝ(2)）。反铁磁J值与卟啉环的π拓扑结构一致。
