The 119 Sn cross polarization-magic angle spinning NMR spectrum of bis[1,3-bis(3-oxapentamethylenecarbamoylthioacetato)-1,1,3,3-tetrabutyl-1,3-distannoxane], {[(C 4 H 9 ) 2 SnO 2 CCH 2 S C(O)N(CH 2 CH 2 ) 2 O] 2 O} 2 , which consists of two resonances of similar chemical shifts and symmetry (d iso = Γ152, Γ202 ppm; asymmetry, k = 0.38), implies the existence of two fivecoordinate tin sites in the centrosymmetric dimer. The assignment has been corroborated by X-ray diffraction analysis on the compound that has been crystallized from ethanol; the crystal structure shows two tin atoms in cis-C 2 SnO 3 trigonal-bipyramidal coordination [C-Sn-C = 131.5(1), 131.3(2) Β°]. The analysis also reveals the presence of two lattice ethanol molecules that are hydrogen-bonded to the dimer [OΓ Γ ΓO = 2.779(5) A Λ]. When exposed to air, the distannoxane loses ethanol. The unsolvated distannoxane is more active than cis-platin when screened against MCF-7 (mammary cancer), EVSA-T (mammary cancer), WiDr (colon cancer), IGROV (ovarian cancer), M19 MEL (melanoma), A498 (renal cancer) and H226 (lung cancer) cell lines.