### Two isomers Ba5Mg4C54O48H114 and Pb5Mg4C54O48H114

Erika Samolová, Michal Dušek
Published: 17 August 2022

Abstract: There are reported two related structures of Ba5Mg4C54O48H114 (dodeca(aqua-6κ3O,7κ3O,8κ3O,9κ3O)-tris(μ2-propanoato-1:6κ2O,1κO′)-tris(μ-propanoato-2:7κ2O,2κO′-tris(μ-propanoato-3:8κ2O,3κO′)-tris(μ-propanoato-4:9κ2O,4κO′)-hexakis(μ3-propanoato-1:5κ2O,2:5κ2O′;1:5κ2O,3:5κ2O′;1:5κ2O,4:5κ2O′;2:5κ2O,3:5κ2O′;2:5κ2O,4:5κ2O′;3:5κ2O,4:5κ2O′)-pentabarium tetramagnesium), (I), and Pb5Mg4C54O48H114 (dodeca(aqua-1κ3O,2κ3O,3κ3O,4κ3O)-hexakis(μ3-propanoato-1:5κ2O,2:5κ2O′;1:5κ2O,3:5κ2O′;1:5 κ2O,4:5κ2O′;2:5κ2O,3:5κ2O′;2:5κ2O,4:5κ2O′;3:5κ2O,4:5κ2O′)tetramagnesium lead(II) tris(propanoato-κ2O,O′)plumbate(II)), (II). The title structures are compositional isomers which crystallize in the same space group type. The structure of (I) comprises molecules with symmetry 4 ‾ 3 m $\overline{4}3m$ . The structure (II) comprises the complex cation {Pb(C3H5O2)6[Mg(H2O)3]4}4+ with the symmetry 4 ‾ 3 m $\overline{4}3m$ and four anions [tris(propanoato-κ2O,O′)plumbate(II)], [Pb(C3H5O2)3] , with 3m symmetry. The central cations Ba12+ and Pb12+ in (I) and in the cation {Pb(C3H5O2)6[Mg(H2O)3]4}4+ of the structure (II), respectively, have similar structural features which are comparable to the environment of the Ba2+ cation in BaCa2(C3H5O2)6 [Stadnicka, K. & Glazer, A. M. (1980). Acta Cryst. B36, 2977–2985]. The molecules in (I) and the ions in (II) are interconnected by Owater‒H⋯Opropanoate hydrogen bonds of a moderate strength. The ethyl chains are disordered which is common in propanoates. However, there are unprecedented features in the title structures: 1) The central atom Pb12+ is the first known example of a Pb2+ cation which is surrounded by six carboxylates in a bidentate bridging mode, i.e. by 12 oxygens. 2) The anion [tris(propanoato-κ2O,O′)plumbate(II)] has a constitution with unusually prominent stereochemical activity of the 6s2 electron pair of the cation Pb2+ completing the coordination to the tetrahedral one. Thus, its formula can be expressed as [Pb[ψ−4t](C3H5O2)3]. 3) In both title structures, there are propanoate molecules with disordered carboxylate oxygens.
Keywords: positional disorder of the carboxylate oxygens / positional disorder of the ethyl chains / propanoates / stereochemical 6s2 lone pair activity in Pb2+

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