Solid-state 25Mg NMR spectroscopic and computational studies of organic compounds. square-pyramidal magnesium(II) ions in aqua(magnesium) phthalocyanine and chlorophyll a.
Solid-state 25Mg NMR spectroscopic and computational studies of organic compounds. square-pyramidal magnesium(II) ions in aqua(magnesium) phthalocyanine and chlorophyll a.
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DOI：
10.1021/jp061350w
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发表时间：
2006-08
期刊：
影响因子：
--
通讯作者：
A. Wong;R. Ida;X. Mo;Z. Gan;J. Poh;Gang Wu
中科院分区：
文献类型：
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作者：
A. Wong;R. Ida;X. Mo;Z. Gan;J. Poh;Gang Wu
我们报道了两种含镁有机化合物的固态(25 Mg)核磁共振波谱研究：单吡啶化水(镁)酞菁(MgPc.H(2)O.Py)和叶绿素a(Chla)。这些化合物中的每一个都含有一个与四个氮原子配位的镁(II)离子和一个方形金字塔几何构型的水分子。用Hahn-ECHO和四极Carr-Purcell Meiom-Gill(QCPMG)脉冲序列，在11.7T(对(1)H为500 MHz)下，对(25)个富镁样品(99.1%(25)个镁原子)进行了固态(25)mg核磁共振谱的测量。在19.6T(对(1)H为830 MHz)下，在25 mg自然丰度(10.1%)下记录了Chla的固体(25)mg核磁共振谱。(25)镁四极参数由光谱分析得到：MgPc.H(2)0.Py，C(Q)=13.0+/-0.1 MHz，Eta(Q)=0.00+/-0.05，Chla，C(Q)=12.9+/-0.1 MHz，Eta(Q)=1.00+/-0.05。这项工作是第一次用固体(25)镁核磁共振波谱表征了方锥几何构型的镁离子。在限制HarteFock(RHF)、密度泛函理论(DFT)和二阶Møller-Plesset微扰理论(MP2)水平上对这两种化合物的电场梯度(EFG)和化学屏蔽张量进行了大量的量子力学计算。在RHF和MP2水平上计算的(25)Mg核四极耦合常数在cc-pV5Z基组上表现出合理的基组收敛(在实验值的7%以内)；然而，B3LYP结果显示在cc-pVTZ基组之外有很大的发散。本文还报道了一种新的晶体结构--MgPc.H(2)OPy。
We report a solid-state (25)Mg NMR spectroscopic study of two magnesium-containing organic compounds: monopyridinated aqua(magnesium) phthalocyanine (MgPc.H(2)O.Py) and chlorophyll a (Chla). Each of these compounds contains a Mg(II) ion coordinating to four nitrogen atoms and a water molecule in a square-pyramidal geometry. Solid-state (25)Mg NMR spectra for MgPc.H(2)O.Py were obtained at 11.7 T (500 MHz for (1)H) for a (25)Mg-enriched sample (99.1% (25)Mg atom) using both Hahn-echo and quadrupole Carr-Purcell Meiboom-Gill (QCPMG) pulse sequences. Solid-state (25)Mg NMR spectra for Chla were recorded at (25)Mg natural abundance (10.1%) at 19.6 T (830 MHz for (1)H). The (25)Mg quadrupole parameters were determined from spectral analyses: MgPc.H(2)O.Py, C(Q) = 13.0 +/- 0.1 MHz and eta(Q) = 0.00 +/- 0.05; Chla, C(Q) = 12.9 +/- 0.1 MHz and eta(Q) = 1.00 +/- 0.05. This work represents the first time that Mg(II) ions in a square-pyramidal geometry have been characterized by solid-state (25)Mg NMR spectroscopy. Extensive quantum mechanical calculations for electric-field-gradient (EFG) and chemical shielding tensors were performed at restricted Hartee-Fock (RHF), density functional theory (DFT), and second-order Møller-Plesset perturbation theory (MP2) levels for both compounds. Computed (25)Mg nuclear quadrupole coupling constants at the RHF and MP2 levels show a reasonable basis-set convergence at the cc-pV5Z basis set (within 7% of the experimental value); however, B3LYP results display a drastic divergence beyond the cc-pVTZ basis set. A new crystal structure for MgPc.H(2)O.Py is also reported.