On the origin of the inverted stability order of the reverse-Keggin [(MnO4)(CH3)12Sb12O24]6-: a DFT study of alpha, beta, gamma, delta, and epsilon isomers.
Density functional theory calculations have been carried out to investigate the alpha, beta, gamma, delta, and epsilon isomers of [(MnO(4))Me(12)Sb(12)O(24)](6-) (Me = CH(3)) anions, which are simplified Baker-Figgis models of Keggin-type antimonate complexes in experiments. It is found that the stability order of the five isomers (alpha < beta < gamma < delta < epsilon) perfectly reverses to the well-known trend of the classical Keggin [PW(12)O(40)](3-) anions (alpha > beta > gamma > delta > epsilon), despite their significant similarities in frameworks. On the basis of the building block decomposition method, the stabilizing effect of the edge-sharing [Sb(2)(mu-O)(2)Me(2)] fragment inside gamma, delta, and epsilon structures is confirmed and found to originate from its two energy-favorable components rather than itself as an indivisible unit. Similar behavior is also held by the destabilizing [W(2)(mu-O)(2)O(2)] fragment in [PW(12)O(40)](3-); however, the well-accepted electrostatic repulsion between the short W(VI)-W(VI) contacts cannot be taken as direct evidence. Notably, in the assembly of the [(MnO(4))Me(12)Sb(12)O(24)](6-) structure, all of the octahedral building units incline to compress axially and elongate horizontally, and this is exactly opposite to the deformation pattern observed in the building blocks of Keggin tungstates, which tend to elongate axially and compress horizontally, thus giving rise to the inverted stability order. Furthermore, energy decomposition analysis reveals that the intrinsic property of the anion comes from the spatial arrangements of the metal-oxygen cage and does not change significantly with the type and charge of the encapsulated anion.
Zhang
Fu-Qiang
FQ
Department of Chemistry, Shangqiu Normal University, Shangqiu 476000, People's Republic of China.
Guan
Wei
W
Zhang
Yin-Tang
YT
Xu
Mao-Tian
MT
Li
Jian
J
Su
Zhong-Min
ZM
D000965:Antimony / Q000737:chemistry*; D003198:Computer Simulation; D007536:Isomerism; D008345:Manganese / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D013237:Stereoisomerism
D009942:Organometallic Compounds; D008345:Manganese; D000965:Antimony