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Characterization of Water Coordination to Ferrous Nitrosyl Complexes with fac-N2O, cis-N2O2, and N2O3 Donor Ligands
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2015-06-19 00:00:00 , DOI: 10.1021/acs.inorgchem.5b00788
John McCracken 1 , Patrick J. Cappillino 2, 3 , Joshua S. McNally 2 , Matthew D. Krzyaniak 1 , Michael Howart 1 , Paul C. Tarves 2 , John P. Caradonna 2
Affiliation  

Electron paramagnetic resonance (EPR) experiments were done on a series of S = 3/2 ferrous nitrosyl model complexes prepared with chelating ligands that mimic the 2-His-1-carboxylate facial triad iron binding motif of the mononuclear nonheme iron oxidases. These complexes formed a comparative family, {FeNO}7(N2Ox)(H2O)3–x with x = 1–3, where the labile coordination sites for the binding of NO and solvent water were fac for x = 1 and cis for x = 2. The continuous-wave EPR spectra of these three complexes were typical of high-spin S = 3/2 transition-metal ions with resonances near g = 4 and 2. Orientation-selective hyperfine sublevel correlation (HYSCORE) spectra revealed cross peaks arising from the protons of coordinated water in a clean spectral window from g = 3.0 to 2.3. These cross peaks were absent for the {FeNO}7(N2O3) complex. HYSCORE spectra were analyzed using a straightforward model for defining the spin Hamiltonian parameters of bound water and showed that, for the {FeNO}7(N2O2)(H2O) complex, a single water conformer with an isotropic hyperfine coupling, Aiso = 0.0 ± 0.3 MHz, and a dipolar coupling of T = 4.8 ± 0.2 MHz could account for the data. For the {FeNO}7(N2O)(H2O)2 complex, the HYSCORE cross peaks assigned to coordinated water showed more frequency dispersion and were analyzed with discrete orientations and hyperfine couplings for the two water molecules that accounted for the observed orientation-selective contour shapes. The use of three-pulse electron spin echo envelope modulation (ESEEM) data to quantify the number of water ligands coordinated to the {FeNO}7 centers was explored. For this aspect of the study, HYSCORE spectra were important for defining a spectral window where empirical integration of ESEEM spectra would be the most accurate.

中文翻译:

具有fac -N 2 O,顺式-N 2 O 2和N 2 O 3供体配体的亚硝酸亚铁配合物水配位的表征

电子顺磁共振(EPR)实验在一系列完成小号= 3 / 2与螯合配位体来制备亚硝基亚铁络合物模型模仿2-他-1-羧酸面部三联铁结合单核非血红素铁氧化酶基序。这些复合物形成的比较家庭,{} FeNO水平7(N 2 ö X)(H 2 O)3- XX = 1-3,其中对于NO和溶剂水的结合不稳定配位点分别为FAC X = 1和x = 2的顺式。这三种配合物的连续波EPR光谱是高自旋的典型特征小号= 3 / 2的过渡金属离子与邻近共振= 4和2。取向选择性超精细分段的相关性(HYSCORE)光谱显示在一个干净的光谱窗口从配位水的质子产生的从交叉峰= 3.0〜2.3。{FeNO} 7(N 2 O 3)络合物不存在这些交叉峰。使用直接模型定义结合水的自旋哈密顿参数对HYSCORE光谱进行了分析,结果表明,对于{FeNO} 7(N 2 O 2)(H 2 O)络合物,具有各向同性超精细偶联的单一水构象异构体,= 0.0±0.3兆赫,和一个偶极耦合Ť = 4.8±0.2兆赫可以解释的数据。对于{FeNO} 7(N 2 O)(H 2 O)2络合物,分配给配位水的HYSCORE交叉峰显示出更大的频率色散,并通过离散取向和超精细偶合对两个水分子进行了分析,这是观察到的。方向选择轮廓形状。使用三脉冲电子自旋回波包络调制(ESEEM)数据来量化与{FeNO} 7配位的水配体的数量探索中心。对于该研究的这一方面,HYSCORE光谱对于定义光谱窗口至关重要,在该窗口中,ESEEM光谱的经验积分将是最准确的。
更新日期:2015-06-19
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