The redox and acidic properties of α-Keggin anions[PW_(11)O_(39)ME]^(4−)(M=Nb,Ta;E=O,S,Se)have been investigated by using the density functional theory(DFT)method.The calculated results for the studied clusters are c...The redox and acidic properties of α-Keggin anions[PW_(11)O_(39)ME]^(4−)(M=Nb,Ta;E=O,S,Se)have been investigated by using the density functional theory(DFT)method.The calculated results for the studied clusters are consistent with the hypothesis that the substitution of one O atom by S or Se atoms in polyoxometalates(POMs)modifies the relative energy of the lowest unoccupied molecular orbital,inducing slight changes in the redox properties of POMs.The electronic structures and reduction energies of[PW_(11)O_(39)ME]^(4−)(M=Nb,Ta;E=O,S,Se)confirm that the substitution of one O atom by S and Se atoms in POMs enhances the redox properties,which is in good agreement with the cyclic voltammetry characterization of α-[PW+(11)NbO_(40)]^(4−) and α-[PW_(11)NbSO_(39)]^(4−).The bonding energies for adding the first proton to the anions and for ammonia coordination to the protonated α-[PW_(11)O_(39)NbE]^(4−)(E=O,S,Se)were simulated to study the basicity of external oxygen sites and the acidity.The results show that the protonation energy becomes more positive after substitution by S and Se,indicating that the substitution enhances the acidity of POMs.The adsorption energy of ammonia in the case of α-[PW_(11)O_(39)NbE]^(4−)(E=S,Se)is more negative than that of α-[PW_(11)O_(40)NbO]^(4−),which also provides the same result as mentioned above.展开更多
基金financial support by the NSFC(21073030 and 21131001)the Program for New Century Excellent Talents in University(NCET-10-318)+1 种基金the Doctoral Fund of the Ministry of Education of China(20100043120007)the Science and Technology Development Planning of Jilin Province(20100104 and 20100320).
文摘The redox and acidic properties of α-Keggin anions[PW_(11)O_(39)ME]^(4−)(M=Nb,Ta;E=O,S,Se)have been investigated by using the density functional theory(DFT)method.The calculated results for the studied clusters are consistent with the hypothesis that the substitution of one O atom by S or Se atoms in polyoxometalates(POMs)modifies the relative energy of the lowest unoccupied molecular orbital,inducing slight changes in the redox properties of POMs.The electronic structures and reduction energies of[PW_(11)O_(39)ME]^(4−)(M=Nb,Ta;E=O,S,Se)confirm that the substitution of one O atom by S and Se atoms in POMs enhances the redox properties,which is in good agreement with the cyclic voltammetry characterization of α-[PW+(11)NbO_(40)]^(4−) and α-[PW_(11)NbSO_(39)]^(4−).The bonding energies for adding the first proton to the anions and for ammonia coordination to the protonated α-[PW_(11)O_(39)NbE]^(4−)(E=O,S,Se)were simulated to study the basicity of external oxygen sites and the acidity.The results show that the protonation energy becomes more positive after substitution by S and Se,indicating that the substitution enhances the acidity of POMs.The adsorption energy of ammonia in the case of α-[PW_(11)O_(39)NbE]^(4−)(E=S,Se)is more negative than that of α-[PW_(11)O_(40)NbO]^(4−),which also provides the same result as mentioned above.
