基于密度泛函理论(DFT)M06L方法对一系列单锰取代的Keggin型POM吸附大气小分子X(X=H2O,N2,O2,NO,N2O,CO和CO2)配合物的分子几何,电子结构和成键性质进行了系统研究.由于POM的多阴离子性质,铯盐Cs4[PW11O39MnⅢH2O]被用来考虑抗衡离子效应.DFT-M06L计算表明,当改变4个Cs抗衡阳离子的位置时,多酸阴离子的几何结构和电子结构参数几乎没有变化.当不考虑抗衡离子效应,在气相和溶液中单独优化多酸阴离子([PW11O39MnⅢH2o]4-)时,其主要几何和电子参数没有显著变化.比较不同白旋态的能量表明[PW11O39MnⅡX]4-(X=H2O、N2、N2O、CO和CO2)的最低能量态是高自旋五重态,[PW11O39MnⅢ O2]4-为三重态,而[PW11O39MnⅢNO]4-则为双重态.这些大气小分子在类卟啉POM配体上的吸附能量按照以下顺序增加:N2＜N2O＜CO≈CO2＜O2＜H2O＜NO.POM-Mn-NO配合物具有较大的吸附能.Mulliken布居分析表明,NO配体与多酸中MnⅢ中心的相互作用主要来自于中间白旋态的MnⅢ中心与NO分子之间的反铁磁性耦合相互作用.%Geometries,electronic structure,and bonding nature of a series of mono-manganese-substituted Keggin-type (POMs) with atmospheric small molecules X (X=H2O,N2,O2,NO,N2O,CO and CO2) have been studied based on density functional theory (DFT) method with M06L functional.Due to the poly-anionic nature of polyoxometalates (POMs),the counterions effects have firstly been considered by means of a full treatment of the cesium salt CS4 [PW11O39MnⅢH2O].DFT-M06L calculations show that the key geometric a nd electronic parameters are almost constants as change of the four Cs counterions.The optimized calculations for [PW11O39MnⅢ H2O]4-both in gas phase and solution provide an analogous result,no significant variation of key geometric and electronic parameters was found when compared with the cesium salt.The calculated relative energy of different spin states indicates that the lowest energy spin state is the high-spin quintet state for [PW11O39MnⅢX]4-(X=H2O,N2,N2O,CO and CO2),triplet state for [PW11O39MnⅢO2]4-,and doublet state for [PW11O39MnⅢNO]4-.The calculated adsorption energy of those atmospheric small molecules over the porphyrin-like POM ligand increases in the following order:N2＜N2O＜CO ≈CO2＜O2＜H2O＜NO.The Mn-NO POM complex provides considerable adsorption energy.Mulliken population analysis shows that coordination of NO ligand to the Mn Ⅲ center in its doublet ground state arises from an antiferromagnetic coupling between an intermediate-spin MnⅢ center and NO unit.
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