Bis(bicyclo[2.2.1]hept-5-ene-2-carboxylato)-1κ2 O,O′;4κ2 O,O′-di-μ2-chlorido-1:2κ2 Cl;3:4κ2 Cl-octamethyl-1κ2 C,2κ2 C,3κ2 C,4κ2 C-di-μ3-oxido-1:2:3κ3 O;2:3:4κ3 O-tetratin(IV)

In the title compound, [Sn4(CH3)8(C8H9O2)2Cl2O2], the tetranuclear complex molecule has crystallographically imposed inversion symmetry. The coordination polyhedron about the two central Sn atoms is distorted trigonal–bipyramidal, whilst the two peripheral metal atoms bonded to the carboxylate groups have a distorted octahedral coordination geometry. In the crystal, molecules are connected by long Sn⋯O contacts [3.139 (11) Å], forming chains along [011].

In the title compound, [Sn 4 (CH 3 ) 8 (C 8 H 9 O 2 ) 2 Cl 2 O 2 ], the tetranuclear complex molecule has crystallographically imposed inversion symmetry. The coordination polyhedron about the two central Sn atoms is distorted trigonalbipyramidal, whilst the two peripheral metal atoms bonded to the carboxylate groups have a distorted octahedral coordination geometry. In the crystal, molecules are connected by long SnÁ Á ÁO contacts [3.139 (11) Å ], forming chains along [011].

Related literature
For the biological activity of organotin compounds, see: Dubey & Roy (2003). For a related structure, see: Li et al. (2006).

Comment
In recent years, organotin compounds have attracted more and more attention due to their wide range of industrial applications and biological activities (Dubey & Roy, 2003). As a part of our ongoing investigations in this field, we have synthesized the title compound and present its crystal structure here.
The tetranuclear complex molecule of the title compound ( Fig. 1) has crystallographically imposed inversion symmetry.
The tin atoms have two different coordination modes, one atom (Sn2) is coordinated in a distorted trigonal-bipyramidal geometry by one µ 3 oxo oxygen atom and two methyl groups forming the equatorial plane, and by an µ 3 oxo oxygen atom and the chloride anion at the apices; the other tin metal (Sn1) has a distorted octahedral coordination geometry, with three O atoms and one Cl atom in equatorial positions and the axial position occupied by two methyl groups. The Sn-O bond distances involving the carboxylate group (Sn1-O2 = 2.115 (8) Å; Sn1-O3 = 2.699 (9) Å) are comparable to those found in a related organotin carboxylate (Li et al., 2006). The shortest Sn···Sn separation within the Sn 4 core is 3.2898 (10) Å.

Experimental
The reaction was carried out under a nitrogen atmosphere. Bicyclo[2.2.1]heptane-2-carboxylic acid (1 mmol) and sodium ethoxide (1 mmol) were added to a stirred solution of benzene (30 ml) in a Schlenk flask After stirring the solution for 30 min, dimethyltin dichloride (2 mmol) was added and the reaction mixture was stirred for 12 h at room temperature. The