Swiderski G, Kalinowska M, Wojtulewski S, Lewandowski W
Department of Chemistry, Białystok Technical University, Zamenhofa 29, 15-435 Białystok, Poland.
Spectrochim Acta A Mol Biomol Spectrosc. 2006 May 1;64(1):24-33. doi: 10.1016/j.saa.2005.06.034. Epub 2005 Aug 10.
The experimental IR, Raman, and 1H NMR spectra of picolinic acid, as well as magnesium, calcium, strontium, and barium picolinates were registered, assigned and studied. Characteristic changes in the spectra of metal picolinates in comparison with the spectrum of ligand were observed, which lead to the conclusion that perturbation of the aromatic system of picolinates increases along with the series Mg-->Ca-->Sr-->Ba. Theoretical structures of beryllium and magnesium picolinates, as well as theoretical IR spectrum of magnesium picolinate were calculated in B3PW91/6-311++G(d, p) level. On the basis of calculated bond lengths in pyridine ring geometric, aromaticity indexes HOMA were calculated. The idea of these indexes is based on the fact that the essential factor in aromatic stabilization is the pi delocalization manifested in: planar geometry, equalization of the bond lengths and angles, and symmetry. The decidedly lower value of HOMA for magnesium picolinate (i.e. 0.545; 0.539) than that for beryllium picolinate (i.e. 0.998; 0.998) indicate higher aromatic properties of Be picolinate than of Mg picolinate. The comparison of theoretical and literature experimental structures of magnesium picolinate was done. The experimental structure contains two water molecules, so the calculations for hydrated magnesium picolinate were carried on, and the influence of coordinated water molecule on the structure of picolinates was discussed. The HOMAs for hydrated experimental and calculated Mg picolinate amount to 0.870; 0.743, and 0.900; 0.890, respectively, whereas for anhydrous structure, it is as described above, i.e. 0.545; 0.539. Thus, the calculations clearly showed that water molecules coordinated to the central atom weakens the effect of metal on the electronic system of ligand.
记录、归属并研究了吡啶甲酸以及吡啶甲酸镁、钙、锶和钡的实验红外光谱、拉曼光谱和¹H核磁共振光谱。观察到吡啶甲酸盐金属盐光谱相对于配体光谱的特征变化，这导致得出结论：吡啶甲酸盐芳香体系的扰动随着Mg→Ca→Sr→Ba系列而增加。在B3PW91/6 - 311++G(d, p)水平上计算了吡啶甲酸铍和镁的理论结构以及吡啶甲酸镁的理论红外光谱。基于吡啶环几何结构中计算出的键长，计算了芳香性指数HOMA。这些指数的概念基于这样一个事实，即芳香稳定化的关键因素是π离域，表现为：平面几何结构、键长和键角的均等化以及对称性。吡啶甲酸镁的HOMA值（即0.545；0.539）明显低于吡啶甲酸铍的HOMA值（即0.998；0.998），表明吡啶甲酸铍的芳香性质高于吡啶甲酸镁。对吡啶甲酸镁的理论结构和文献实验结构进行了比较。实验结构包含两个水分子，因此对水合吡啶甲酸镁进行了计算，并讨论了配位水分子对吡啶甲酸盐结构的影响。水合实验和计算得到的吡啶甲酸镁的HOMA值分别为0.870；0.743和0.900；0.890，而无水结构的HOMA值如上所述，即0.545；0.539。因此，计算结果清楚地表明，与中心原子配位的水分子削弱了金属对配体电子体系的影响。
