Crystal and solution structures of calcium complexes relevant to problematic waste disposal: calcium gluconate and calcium isosaccharinate

The single‐crystal structures of calcium d‐gluconate and calcium α‐d‐isosaccharinate have been determined using X‐ray diffraction at 100 K. Surprisingly, given its significance in industrial and medical applications, the structure of calcium d‐gluconate has not previously been reported. Unexpectedly...

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Bibliographic Details
Published in:	Acta crystallographica Section B, Structural science, crystal engineering and materials Vol. 74; no. 6; pp. 598 - 609
Main Authors:	Bugris, V., Dudás, Cs, Kutus, B., Harmat, V., Csankó, K., Brockhauser, S., Pálinkó, I., Turner, Peter, Sipos, P.
Format:	Journal Article
Language:	English
Published:	5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01-12-2018 Blackwell Publishing Ltd
Subjects:	Calcium Coordination numbers Coordination polymers Crystal structure gluconate Hydrogen bonds intermediate‐level waste repositories isosaccharinate Ligands low‐level waste repositories Metals Molecular conformation Polymers Radiation Synchrotron radiation Waste disposal X-ray diffraction
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Summary:	The single‐crystal structures of calcium d‐gluconate and calcium α‐d‐isosaccharinate have been determined using X‐ray diffraction at 100 K. Surprisingly, given its significance in industrial and medical applications, the structure of calcium d‐gluconate has not previously been reported. Unexpectedly, the gluconate crystal structure comprises coordination polymers. Unusually, the calcium coordination number is nine. Adjacent metal centres are linked by three μ‐oxo bridges, with a metal–metal separation of 3.7312 (2) Å. One of the gluconate ligands contradicts a suggestion from 1974 that a straight chain conformation is associated with an intramolecular hydrogen bond. This ligand binds to three adjacent metal centres. The use of synchrotron radiation provided an improved crystal structure with respect to that previously reported for the isosaccharinate complex, allowing the location of the hydroxy hydrogen sites to be elucidated. In contrast to the gluconate structure, there are no μ‐oxo bridges in the isosaccharinate coordination polymer and the isosaccharinate bridging coordination is such that the distance between adjacent metal centres, each of which is eight‐coordinate, is 6.7573 (4) Å. Complementing the crystal structure determinations, modelling studies of the geometries and coordination modes for the aqueous [CaGluc]+ and [CaIsa]+ complexes are presented and discussed. The crystal structures of calcium d‐gluconate and calcium α‐d‐isosaccharinate nave been determined, the latter using a synchrotron source, and found to be coordination polymers. Computational studies complement the structure determinations.
ISSN:	2052-5206 2052-5192 2052-5206
DOI:	10.1107/S2052520618013720