Crystal structures of two bi­cyclo­[5.1.0]octa­nes: potassium trans-bi­cyclo­[5.1.0]octane-4-carboxyl­ate monohydrate and cis-bi­cyclo­[5.1.0]octan-4-yl 4-bromo­benzene­sulfonate

The crystal structures of the trans-fused compound potassium trans-bi­cyclo­[5.1.0]octane-4-carboxyl­ate monohydrate, K(+)·C(9)H(13)O(2) (−)·H(2)O, (I), and of cis-bi­cyclo­[5.1.0]octan-4-yl 4-bromo­benzene­sulfonate, C(14)H(17)BrO(3)S, (II), have been determined. Compound (I) represents the smallest trans-fused cyclo­propane structure known to date, and features the expected shortening of the bridging C—C bond relative to the other cyclo­propane bond lengths, in contrast to the cis-fused system, (II), where all of the cyclo­propane bond lengths are the same. The bicyclic ring system of (I) is disordered across a crystallographic mirror plane. The geometries of the cis-fused and trans-fused ring systems are compared.