Abstract
The title compound, {[Ba7(C3H5O2)14]·0.946C3H6O2·4H2O} n , is represented by a metal-organic framework structure that is held together by Ba-O-Ba bonds, as well as by O-H⋯O hydrogen bonds of moderate strength. The structure comprises of four independent Ba2+ cations (one of which is situated on a twofold rotation axis), seven independent propionate and two independent water mol-ecules. The bond-valence sums of all the cations indicate a slight overbonding. There is also an occupationally, as well as a positionally disordered propionic acid mol-ecule present in the structure. Its occupation is slightly lower than the full occupation while the disordered mol-ecules occupy two positions related by a rotation about a twofold rotation axis. In addition, the methyl group in the symmetry-independent propionic acid mol-ecule is also disordered, and occupies two positions. Each propionic acid mol-ecule coordinates to just one cation from a pair of symmetry-equivalent Ba2+ sites and is simultaneously bonded by an O-H⋯Opropionate hydrogen bond. This means that on a microscopic scale, the coordination number of the corresponding Ba2+ site is either 9 or 10. The methyl as well as hy-droxy hydrogen atoms of the disordered propionic acid mol-ecule were not determined.
Highlights
The title compound, {[Ba7(C3H5O2)14]Á0.946C3H6O2Á4H2O}n, is represented by a metal–organic framework structure that is held together by Ba—O—Ba bonds, as well as by O—HÁ Á ÁO hydrogen bonds of moderate strength
The structure comprises of four independent Ba2+ cations, seven independent propionate and two independent water molecules
Its occupation is slightly lower than the full occupation while the disordered molecules occupy two positions related by a rotation about a twofold rotation axis
Summary
A relatively low number of structurally determined metal propionates with divalent cations are known so far, as manifested by comparison of the numbers of propionates, acetates and formates with alkaline-earth cations which were retrieved from the Cambridge Structural Database (Groom et al, 2016; version 5.40 from November 2018). Numerical details of hydrogenbonding interactions are provided, excluding the Opropionic acid—HÁ Á ÁOpropionate hydrogen bond along O16Á Á ÁO4vii [2.706 (13) A ; symmetry code: (vii) Àx + 1, Ày, Àz + 1] that is donated by the free propionic acid molecule This molecule is disordered over two positions related by (Àx + 1, y, Àz + 12) about a twofold rotation axis (Wyckoff position c). Tionality included in PLATON (Spek, 2015), yielded a value of 0.431 This means that the occupation of the disordered molecule is not full; analysis of the bond-valence sum for Ba32+ still points to a slight overbonding (Table 1) even without the presence of propionic acid. The displacement parameter of C24b was constrained to that of C22 (Fig. 5a)
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