Crystal structure of dicesium hydrogen citrate from laboratory single-crystal and powder X-ray diffraction data and DFT comparison.

Alagappa Rammohan,James A Kaduk,Amy A Sarjeant

doi:10.1107/s2056989017000792

Abstract

The crystal structure of dicesium hydrogen citrate, 2Cs+·C6H6O72-, has been solved using laboratory X-ray single-crystal diffraction data, refined using laboratory powder X-ray data, and optimized using density functional techniques. The Cs+ cation is nine-coordinate, with a bond-valence sum of 0.92 valence units. The CsO9 coordination polyhedra share edges and corners to form a three-dimensional framework. The citrate anion is located on a mirror plane. Its central hy-droxy/carboxyl-ate O-H⋯O hydrogen bond is short, and (unusually) inter-molecular. The centrosymmetric end-end carboxyl-ate hydrogen bond is exceptionally short (O⋯O = 2.416 Å) and strong. These hydrogen bonds contribute 16.5 and 21.7 kcal mol-1, respectively, to the crystal energy. The hydro-phobic methyl-ene groups occupy pockets in the framework.

Highlights

The crystal structure of dicesium hydrogen citrate, 2Cs+C6H6O72, has been solved using laboratory X-ray single-crystal diffraction data, refined using laboratory powder X-ray data, and optimized using density functional techniques
We report here synthesis and crystal structure of another alkali metal citrate salt, 2Cs+HC6H5O72
A single crystal was mounted in inert oil and transferred to the cold gas stream of a Bruker Kappa APEX CCD area detector system equipped with a Cu K sealed tube with MX optics

Summary

Chemical context

In the course of a systematic study of the crystal structures of group 1 (alkali metal) citrate salts to understand the anion’s conformational flexibility, ionization, coordination tendencies, and hydrogen bonding, we have determined several new crystal structures. Most of the new structures were solved using X-ray powder diffraction data (laboratory and/or synchrotron), but single crystals were used where available. The general trends and conclusions about the sixteen new compounds and twelve previously determined structures are being reported separately (Rammohan & Kaduk, 2017a). Eleven of the new structures – NaKHC6H5O7, NaK2C6H5O7, Na3C6H5O7, NaH2C6H5O7, Na2HC6H5O7, K3C6H5O7, Rb2HC6H5O7, Rb3C6H5O7(H2O), Rb3C6H5O7, Na5H(C6H5O7), and CsH2C6H5O7 – have been published recently (Rammohan & Kaduk, 2016a,b,c,d,e, 2017b,c,d,e,f, Rammohan et al, 2016), and two additional structures – KH2C6H5O7 and KH2C6H5O7(H2O)2 – have been communicated to the Cambridge Structural Database (CSD) We report here synthesis and crystal structure of another alkali metal citrate salt, 2Cs+HC6H5O72

Structural commentary

Database survey

Synthesis and crystallization

Refinement

DFT calculations