Structure of Anhydrous Alkali-Metal Formates

Single-crystal X-ray diffraction has yielded new crystal structures for cesium formate (CsOOCH) and rubidium
formate (RbOOCH). The cesium formate structure has the same unit cell and space group as that published from
powder X-ray diffraction data (Masuda, Y.; Yahata, A.; Ogawa, H. Inorg. Chem. 1995, 34, 3130−3133) but differs
radically in the placement and orientation of the formate ions. The new crystal structure has been successfully
modeled with an empirical force field based on pair potentials, whereas it proved impossible to develop a force
field that gave an adequate description of the powder structure. For rubidium formate, the gross structure is similar
to that previously published (Masuda, Y.; Morita, W.; Yahata, A.; Yukawa, Y. Thermochim. Acta 1998, 318, 39−43), but the space group includes a mirror plane (Pbcm rather than Pbc21). From this information, we have been
able to analyze the effect of the cation size on the crystal structure for alkali-metal formates.