The crystal structure of the title complex has been determined. The crystal is space P1 with parameters: a=1.3943(3)nm,b=1.4635(3)m,c=1. 2792(3)nm, α=94.32(3)°,β=116.27(3)°,γ=109.08(3)°，Z=2， V=2. 1362(8)nm^3, Dc=1.542g/cm^3,F(000)=1004, and the structure is refined to final R=0.0401,Rw=0.1076. Four carboxylate ligands are divided into two types. Two of the carboxylate ligands are bidentate (μ-COO) and bridging each pair of endo-and exo-cyclic tin atoms by using both oxygen atoms. The others are monodentate and coordinate each exo cyclic tin atom. Both endo-and exo-cyclic tin atoms are all five- coordination with coordination geometry of monocapped distorted trigonal bipyramid. Two conjugate systems (acryloxy group and Cp ring) can not be coplanar with the central endo-cyclic Sn2O2 unit. The NMR data indicate the existence of a dynamic process of the carboxylic coordination tautomers. Comparing the crystal {[(n-Bu)2Sn(FcCO2)]2O}2 ·4C6H6 (A) with {[(n-Bu)2Sn(FcCO2)]2O}2 (B), we put forward a waggling mechanism to explain this phenomenon, namely, the oxygen atoms of carboxylic groups vacillate quickly within the plane of their carboxylic groups. This is owing to the fluctuations of electron cloud to result in re-distribution or re-adjustment of Sn— O bonds considering completely both the strong and weak interactions between Sn atoms and O atoms rather than the internal rotation about the Sn— O(carboxylic) bonds.

Key words: FERROCENE P, ACRYLIC ACID P, ORGANO TIN COMPOUNDS, CRYSTAL STRUCTURE, COORDINATE CHEMISTRY