Crystal structure analysis of [Ca(O3SC18H37)2(DMSO)2], a lamellar coordination polymer and its relevance for model studies in biomineralization

Abstract

Single crystals of a one-dimensional Ca coordination polymer of the surfactant octadecyl sulfonate (C₁₈H₃₇SO₃⁻) have been grown from hot DMSO solution. The X-ray structure analysis of the compound [Ca(O₃SC₁₈H₃₇)₂(DMSO)₂] (1) shows a lamellar interdigitated arrangement of hydrophobic tails of the amphiphilic ligands. Each Ca ion is coordinated by four different sulfonate groups, and its nearly octahedral coordination environment is completed by two dimethyl sulfoxide (DMSO) ligands. The octadecyl sulfonate ligand coordinates to Ca ions in a µ₂-bridging mode, which contrasts to information from literature suggesting a µ₃-bridging coordination mode. Since the growth of highly oriented calcite single crystals underneath Langmuir monolayers of this particular surfactant is often regarded as textbook example of a heteroepitaxy (“template”) mechanism in biomineralization, we present a critical discussion of the crystal structure of the title compound in this context.