Crystal structures of catena-poly[[μ-aqua-di-aqua(μ(3)-2-methyl-propano-ato-κ(4) O:O,O':O')calcium] 2-methyl-propano-ate dihydrate], catena-poly[[μ-aqua-di-aqua-(μ(3)-2-methyl-propano-ato-κ(4) O:O,O':O')strontium] 2-methyl-propano-ate dihydrate] and catena-poly[[μ-aqua-di-aqua-(μ(3)-2-methyl-propano-ato-κ(4) O:O,O':O')(calcium/strontium)] 2-methyl-propano-ate dihydrate].

The crystal structures of catena-poly[[μ-aqua-di-aqua-(μ(3)-2-methyl-propano-ato-κ(4) O:O,O':O')calcium] 2-methyl-propano-ate dihydrate], {[Ca(C(4)H(7)O(2))(H(2)O)(3)](C(4)H(7)O(2))·2H(2)O} (n) , (I), catena-poly[[μ-aqua-di-aqua-(μ(3)-2-methyl-propano-ato-κ(4) O:O,O':O')strontium] 2-methyl-propano-ate dihydrate], {[Sr(C(4)H(7)O(2))(H(2)O)(3)](C(4)H(7)O(2))·2H(2)O} (n) , (II), and catena-poly[[μ-aqua-di-aqua-(μ(3)-2-methyl-propano-ato-κ(4) O:O,O':O')(calcium/strontium)] 2-methyl-propano-ate dihydrate], {[(Ca,Sr)(C(4)H(7)O(2))(H(2)O)(3)](C(4)H(7)O(2))·2H(2)O} (n) , (III), are related. (III) can be considered as an Sr-containing solid solution of (I), with Ca(2+) and Sr(2+) occupationally disordered in the ratio 0.7936†(16):0.2064†(16). (I)/(III) and (II) are homeotypic with different space groups of Pbca and Cmce, respectively. All the title crystal structures are composed of hydro-philic sheets containing the cations, carboxyl-ate groups as well as water mol-ecules. The hydro-phobic layers, which consist of 2-methyl-propano-ate chains, surround the hydro-philic sheets from both sides, thus forming a sandwich-like structure extending parallel to (001). The cohesion forces within these sheets are the cation-oxygen bonds and O-H⋯O hydrogen bonds of moderate strength. Stacking of these sandwiches along [001] is consolidated by van der Waals forces. The structures contain columns defined by the cation-oxygen inter-actions in which just one symmetry-independent 2-methyl-propano-ate anion is included, together with three water mol-ecules. These mol-ecules participate in an irregular coordination polyhedron composed of eight O atoms around the cation. Additional water mol-ecules as well as the second 2-methyl-propano-ate anion are not part of the coordination sphere. These mol-ecules are connected to the above-mentioned columns by O-H⋯O hydrogen bonds of moderate strength. In (II), the Sr(2+) cation, two of the coordinating water mol-ecules and both anions are situated on a mirror plane with a concomitant positional disorder of the 2-methyl-propyl groups; the non-coordinating water mol-ecule also shows positional disorder of its hydrogen atom.