Hydrogen bond studies. LXXXIV. An X-ray diffraction study of the structures of KHCO₃ and KDCO₃ at 298, 219 and 95 K

Abstract

The crystal structures of normal and deuterated potassium hydrogen carbonate, KHCO3 and KDCO3, have been studied at 298, 219 and 95K using three-dimensional single-crystal X-ray data collected on a semi-automatic Stoe-Philips Weissenberg diffractometer. Both unit cells are monoclinic, containing four formula units and having the centrosymmetric space group P2~/a (chosen to conform with previous work on KHCO3). The cell dimensions at 298K for KHCO3 are: a=15.1725 (11), b=5.6283 (5), c=3.7110 (4) A, fl=104.631 (6) °, V=306.62 A3; and for KDCOa: a=15.1948 (9), b=5.6307 (3), c= 3.7107 (3) A, fl= 104-567 (5) °, V= 307.27 A s. The KHCO3 structure, comprising (HCO3) 2-dimers and K + ions, is isomorphous with its deuterated counterpart. The heavy atoms of each HCOs ion within the centrosymmetric dimer are closely coplanar at all temperatures, the separation between these planes being ~0.22 A. The two symmetry-related O-H...O hydrogen bonds within the dimer have lengths 2"585 (2), 2.592 (2) and 2.591 (2) A at 298, 219 and 95K, respectively. The corresponding lengths in KDCO3 are: 2.607 (2), 2.613 (2) and 2.606 (2) A, implying length increases of 0.022, 0.021 and 0.015 A on deuteration at the three temperatures. The final R(F) values obtained for the refinements of KHCO3 were 0.037, 0.028 and 0.031, respectively. The corresponding values for KDCO3 were 0.034, 0.033 and 0.033.

Hydrogen bond studies. XCII. Disorder in (HCO3)22− and (DCO3)2−2 dimers: a neutron diffraction study of KHCO3 and KDCO3

“…Suitably large single crystals of KHCO3 were grown without difficulty in the same way as the X-ray crystals (Thomas et al, 1974). The crystal used for data collection had a volume of 62.7 mm 3.…”

“…Using the final room-temperature non-hydrogen atom positions from the earlier X-ray investigation (Thomas et al, 1974) as starting values, a series of refinements was made assuming an ordered structure. No evidence for believing that this was not the case had materialized from the earlier X-ray work, even at low temperatures.…”

“…The internal geometries of the disordered (HCO3)~-and (DCO3)~-ions as obtained from refinements 7 (KHCO3) and 6 (KDCO3). The X-ray values (Thomas et al, 1974) are also included for comparison below the neutron values. The figure has been simplified by drawing the centrosymmetrically related H and D atoms as dashed circles.…”

“…It was to this end that the hydrogen-bond situation within the (HCO3) 2-dimers occurring in KHCO3 was studied by X-ray diffraction methods at both room and low temperatures (Thomas, Tellgren & Olovsson, 1974). This work appeared to dispel the earlier suspicion that disorder existed in the structure (Hamilton & Ibers, 1968).…”

Neutron diffraction study of deuterated imidazolium hydrogen maleate: an evaluation of isotope effect on the hydrogen-bond length

“…However, in all these compounds some symmetry operates on the O...O bond causing the effect of isotopic substitution within the bond to be obscured. Isotope-effect studies on compounds having crystallographically unrestricted O...O hydrogen bonds have so far been limited to the crystal structures of KHCO 3 (X-ray) (Thomas, Tellgren & Olovsson, 1974), bis(3-amino-3-methyl-2-butanone oximato)-nickel(II) chloride monohydrate, [Ni(ao-H)2]C1.H20, (neutron) (Hsu, Schlemper & Fair, 1980), quinolinic acid (neutron) (Takusagawa & Koetzle, 1978 0567-7408/80/051104-05501.00…”