Structural chemistry of organotin carboxylates XV. Diorganostannate esters of dicyclohexylammonium hydrogen oxalate. Synthesis, crystal structure and in vitro antitumour activity of bis(dicyclohexyl‐ammonium) bisoxalatodi‐n‐butylstannate and bis(dicyclohexylammonium) μ‐oxalatobis(aquadi‐n‐butyloxalatostannate)

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AbstractDicyclohexylamine, oxalic acid dihydrate and di‐n‐butyltin oxide were reacted in 2:2:1 or 2:3:2 stoichiometries in ethanol solution to yield, respectively bis(dicyclohexylammonium) bisoxalatodi‐n‐butylstannate (1) and bis(dicyclohexylammonium) μ‐oxalatobis(aquadi‐n‐butyloxalatostannate) (2); the hydrate was also obtained upon recrystallization of 1 from moist acetonitrile solution. The crystal structures of the two ammonium stannates have been determined at room temperature. In 1, the tin atom in the dianion exists in a skewtrapezoidal bipyramidal geometry with the basal plane being defined by two bidentate oxalate ligands; each ligand forms asymmetric SnO bonds [SnO 2.348(4), 2.110(4) Å and 2.112(4), 2.363(4) Å]. The apical sites are occupied by the two organo groups disposed over the weaker SnO bonds. In 2, the two tin centres of the dianion are connected via a tetradentate oxalate ligand situated about a centre of inversion and each tin atom exists in a pentagonal bipyramidal geometry. The pentagonal plane is defined by four oxygen atoms, two from the central ligand [SnO 2.282(4), 2.473(4)Å] and two from a ‘terminal’ oxalate ligand [SnO 2.239(4), 2.210(4)Å], and the fifth site is occupied by a water molecule of crystallization [SnO 2.422(4)Å]; the apical sites are filled by the n‐butyl groups. Both compounds feature extended hydrogen‐bonded networks involving the oxygen atoms of the dianion and the N‐bound hydrogen atoms. Crystals of 1 are monoclinic, space group P21/n, with cell dimensions a = 13.408(3), b = 22.461(4), c = 13.996(2)Å, β = 100.97(2)°; full‐matrix least‐squares refinement on 3305 reflections with I≥2.5σ(I) converged to R = 0.042 and Rw = 0.046. Crystals of 2 are monoclinic, space group P21/n, a = 13.729(3), b = 14.694(2), c = 14.889(2)Å, β = 104.83(2)º; refinement on 2093 reflections converged to R = 0.030 and Rw = 0.031. The two di‐n‐butylstannates were screened in vitro against the mammary MCF‐7 and WiDr colon carcinoma cell lines, and were found to be as active as cisplatin, a clinically used antineoplastic drug.