Nakamura Kenichiro, Ikezaki Akira, Ohgo Yoshiki, Ikeue Takahisa, Neya Saburo, Nakamura Mikio
Department of Chemistry, School of Medicine, Toho University, Ota-ku, Tokyo 143-8540, Japan.
Inorg Chem. 2008 Nov 17;47(22):10299-307. doi: 10.1021/ic800674d. Epub 2008 Oct 18.
The electronic structures of six-coordinate iron(III) octaethylmonoazaporphyrins, [Fe(MAzP)L 2] (+/-) ( 1), have been examined by means of (1)H NMR and EPR spectroscopy to reveal the effect of meso-nitrogen in the porphyrin ring. The complexes carrying axial ligands with strong field strengths such as 1-MeIm, DMAP, CN (-), and (t)BuNC adopt the low-spin state with the (d xy ) (2)(d xz , d yz ) (3) ground state in a wide temperature range where the (1)H NMR and EPR spectra are taken. In contrast, the complexes with much weaker axial ligands, such as 4-CNPy and 3,5-Cl 2Py, exhibit the spin transition from the mainly S = 3/2 at 298 K to the S = 1/2 with the (d xy ) (2)(d xz , d yz ) (3) ground state at 4 K. Only the THF complex has maintained the S = 3/2 throughout the temperature range examined. Thus, the electronic structures of 1 resemble those of the corresponding iron(III) octaethylporphyrins, [Fe(OEP)L 2] (+/-) ( 2). A couple of differences have been observed, however, in the electronic structures of 1 and 2. One of the differences is the electronic ground state in low-spin bis( (t)BuNC) complexes. While [Fe(OEP)( (t)BuNC) 2] (+) adopts the (d xz , d yz ) (4)(d xy ) (1) ground state, like most of the bis( (t)BuNC) complexes reported previously, [Fe(MAzP)( (t)BuNC) 2] (+) has shown the (d xy ) (2)(d xz , d yz ) (3) ground state. Another difference is the spin state of the bis(3,5-Cl 2Py) complexes. While [Fe(OEP)(3,5-Cl 2Py) 2] (+) has maintained the mixed S = 3/2 and 5/2 spin state from 298 to 4 K, [Fe(MAzP)(3,5-Cl 2Py) 2] (+) has shown the spin transition mentioned above. These differences have been ascribed to the narrower N4 cavity and the presence of lower-lying pi* orbital in MAzP as compared with OEP.
通过¹H NMR和EPR光谱研究了六配位铁（III）八乙基单氮杂卟啉Fe(MAzP)L₂（1）的电子结构，以揭示卟啉环中中位氮的影响。带有强场强轴向配体（如1-MeIm、DMAP、CN⁻和tBuNC）的配合物在进行¹H NMR和EPR光谱测量的较宽温度范围内采用低自旋态，基态为(dxy)²(dxz, dyz)³。相反，带有弱得多的轴向配体（如4-CNPy和3,5-Cl₂Py）的配合物表现出自旋转变，从298 K时主要的S = 3/2转变为4 K时S = 1/2且基态为(dxy)²(dxz, dyz)³。在所研究的整个温度范围内，只有THF配合物保持S = 3/2。因此，1的电子结构类似于相应的铁（III）八乙基卟啉Fe(OEP)L₂（2）。然而，在1和2的电子结构中观察到了一些差异。其中一个差异是低自旋双（tBuNC）配合物的电子基态。虽然Fe(OEP)(tBuNC)₂像之前报道的大多数双（tBuNC）配合物一样采用(dxz, dyz)⁴(dxy)¹基态，但Fe(MAzP)(tBuNC)₂表现出(dxy)²(dxz, dyz)³基态。另一个差异是双（3,5-Cl₂Py）配合物的自旋态。虽然Fe(OEP)(3,5-Cl₂Py)₂在298 K至4 K范围内保持混合的S = 3/2和5/2自旋态，但Fe(MAzP)(3,5-Cl₂Py)₂表现出上述自旋转变。这些差异归因于与OEP相比，MAzP中N4空腔更窄且存在能量较低的π*轨道。
