Pyrazole/imidazole and pyrazolato/imidazolato complexes of pentacyanoferrate(II/III) and pentaammineruthenium(II/III). LMCT transitions of low-spin d5 complexes
Pyrazole/imidazole and pyrazolato/imidazolato complexes of pentacyanoferrate(II/III) and pentaammineruthenium(II/III). LMCT transitions of low-spin d5 complexes
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五氰基高铁酸盐(II/III)和五氨合钌(II/III)的吡唑/咪唑和吡唑根/咪唑根络合物。
DOI：
10.1021/ic00186a009
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发表时间：
1984
影响因子：
4.6
通讯作者：
R. Shepherd
中科院分区：
文献类型：
--
作者：
Craig R. Johnson;W. Henderson;R. Shepherd
低自旋d5配合物（CN）5 FeL 2-和（NH3）5 RuL 3+与L=咪唑、吡唑或这些母体五元环的许多衍生物（甲基化咪唑和吡唑、苯并咪唑、次黄嘌呤、咖啡因、组氨酸）配位时观察到配体-金属电荷转移带。LMCT光谱带出现在可见光和UV区域。跃迁的起源可以根据咪唑和吡唑的HOMO来确定。吡咯NH的去质子化产生相应的咪唑酯或吡唑酯复合物，LMCT光谱向水溶液光谱的较低能量偏移。对33个咪唑和6个吡唑配体进行了HOMO数据和归属。吡唑配合物在25.0 ℃下的pAfa，μ= 0.10（NaClO 4），已通过分光光度滴定法测定，除非另有说明（配合物，pXa）：（NH3）5 RuL 3+，5.98;（NH3）5CoL 3+，6.07（玻璃电极，μ= 1.0）;（CN）5 FeL 2-，~ 11;（CN）5CoL 2-，10.9（1H NMR滴定，μ= 1.0）。其他配位配体pXa在25 ℃下测定如下：（NH3）5Co（咪唑）3+，9.99（μ= 1.0）;（CN）5Co（ImH）2-，11.4;（NH3）5Co（3-MePyzH）3+，6.7（玻璃电极）;（NH3）5 Ru（3，5-Me 2 PyH）3+，7.21;（NH3）5 Ru（1，2，4-三唑）3+，4.3。当咪唑和吡唑配位到（NH3）5 Ru 3+时，吡咯NH的酸性对于咪唑增加5.3个数量级，对于吡唑增加8.2个数量级，表明中心Ru（III）离子和去质子化位点之间的距离的影响。讨论了不同配位金属中心对萃取的影响以及咪唑或吡唑的贡献对萃取的影响。本文讨论了DL ~+、（NH_3）_5CoL ~（3+）、（CN）_5CoL ~（2+）、（NH_3）_5RuL ~（2+）和（CN）_5FeL ~（3-）（L= 3-甲基吡唑）配合物的NMR谱。研究了1-甲基咪唑金属中心D ~+、（NH_3）_5Co ~（3+）、CH_3 Hg ~+、（CN）_5Co ~（2-）、（NH_3）_5 Ru ~（2+）、（CN）_5 Fe ~（3-）的配位对配合物NMR谱的影响。在这些配合物中，退离作用掩盖了TIP等其它因素，除了（NH3）5 Ru 2+和（CN）5 Fe 3-中心的背键作用使远位（1-甲基咪唑的H（5）或CH 3和吡唑的H（4）和H（5））的位移相反外，所有配位的吡唑、3-甲基吡唑和1-甲基咪唑的共振都向低场移动。组氨酸的咪唑侧链是许多金属酶的配位环境的一部分。[1]咪唑在许多蛋白质的金属位点的结合表明，这种配体具有特别适合其生物学作用的性质。化合物1的咪唑（ImH（1））和咪唑酯（Im”）络合物
Ligand-to-metal charge-transfer bands are observed for the low-spin d5 complexes (CN) 5FeL2-and (NH3) 5RuL3+ with coordination of L= imidzole, pyrazole, or numerous derivatives of these parent five-membered rings (methylated imidazoles and pyrazoles, benzimidazoles, hypoxanthine, caffeine, histidines). The LMCT spectral bands appear in the visible and UV regions. The origin of the transitions may be assigned on the basis of HOMO’s of imidazole and pyrazole. Deprotonation of the pyrrole NH produces the respective imidazolate or pyrazolate complex, with the LMCT spectra shifted to lower energy for aqueous solution spectra. Data and assignments based on HOMO’s of ligands are made for 33 imidazoles and 6 pyrazoles. The pAfa’s of pyrazole complexes at 25.0 C, µ= 0.10 (NaC104), have been determined by spectrophotometric titration unless otherwise specified (complex, pXa):(NH3) 5RuL3+, 5.98;(NH3) 5CoL3+, 6.07 (glass electrode, µ= 1.0);(CN) 5FeL2",~ 11;(CN) 5CoL2-, 10.9 (* H NMR titration, µ= 1.0). Other coordinated ligand pXa’s were determined at 25 C as follows:(NH3) 5Co (imidazole) 3+, 9.99 (µ= 1.0);(CN) 5Co (ImH) 2-, 11.4;(NH3) 5Co (3-MePyzH) 3+, 6.7 (glass electrode);(NH3) 5Ru (3, 5-Me2PyH) 3+, 7.21;(NH3) 5Ru (l, 2, 4-triazole) 3+, 4.3. When imidazole and pyrazole are coordinated to (NH3) 5Ru3+, the acidity of the pyrrole NH increases 5.3 orders of magnitude for imidazole and 8.2 orders of magnitude for pyrazole, indicative of the influence of distance between the central Ru (III) ion and the site of deprotonation. The influence of withdrawal by varying the coordinated metal center and the influence of donation by imidazolate or pyrazolate is discussed. The NMR spectra for complexes of DL+,(NH3) 5CoL3+,(CN); CoL2~,(NH3) 5RuL2+, and (CN) 5FeL3-(L= 3-methylpyrazole) are discussed. The influence of coordination of the following metalcenters of 1-methylimidazole on the NMR spectrum of the respective complexes is reported: D+,(NH3) 5Co3+, CH3Hg+,(CN) sCo2-,(NH3) 5Ru2+,(CN) 5Fe3-. withdrawal overshadows other factors such as TIP in these complexes, and all resonances are shifted downfield for coordinated pyrazole, 3-methylpyrazole, and 1-methylimidazole except for (NH3) 5Ru2+ and (CN) 5Fe3-centers where back-bonding reverses the shiftof remote sites (H (5) or CH3 of 1-methylimidazole and H (4) and H (5) of pyrazole). IntroductionThe imidazole side chain of the amino acid histidine is known to form part of the coordination environment of a large number of metalloenzymes. 1 The incorporation of imidazole in the metal sites of numerous proteins suggests that this ligand has properties particularly suited to its biological role. The imidazole (ImH (1)) and imidazolate (Im") complexes of