B-Potassium sulphate, K2SO4, and potassium chromate, K2CrO4, are isostructural and crystallize in the orthorhombic space group Pnam (z=4) with unit-cell dimensions a=7-476 (3), b= 10.071 (4), c= 5.763 (2)/~, and a= 7.663 (3), b= 10.388 (4), c= 5.922 (3) A respectively. X-ray intensity data sets were collected for the two compounds with a 4-circle diffractometer and the atomic parameters were refined by full-matrix least-squares methods, the R values (on F) converging to 5.1 and 3.3 % respectively. The shortest contacts between potassium and oxygen in the crystals are in the range 2.68 to 2.79/1~, and amongst the shortest contacts there is one potassium atom approximately collinear with each of the bond axes within the anion. The anions have crystallographic, ally imposed rn symmetry. The three independent sulphur-oxygen bond lengths in potassium sulphate are 1-459 (4), 1.473 (4) and 1-472 (5) A. The three independent chromium-oxygen bond lengths in potassium chromate are 1.636 (3), 1.651 (2), and 1.643 (3) A. The crystal forces acting upon the atoms in the anions were calculated using an electrostatic model with a range of charges on the atoms. The crystal force tends to compress the bonds within the anions and there was a linear variation of the observed bond lengths with the calculated force for all reasonable values of the assumed charges. In the absence of crystal forces, the bond lengths are calculated to be 1.473 A for the sulphate anion and 1.653/~, for the chromate anion; applying a thermal motion correction using the riding model yields the best estimate for the sulphur-oxygen bond length in the sulphate anion as 1.486/~ and the chromium-oxygen bond length in the chromate anion as 1.670 .~. A force constant can be derived for the anion bonds and comparison of this with the corresponding force constant derived from infrared spectroscopy indicates that the effective charges upon the atoms in the crystals are approximately 2.0 (for sulphur or chromium), 1.0 (for potassium) and -1.0 (for oxygen). The crystal force calculations were also applied to potassium manganate and potassium selenate using previously reported atomic parameters; the best estimate of the bond lengths in the manganate and selenate anions is 1.675 and 1.650/~ respectively.

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Szmmary The X-ray crystal structure of CsB,HI4 shows the presence of three BH, groups and two B-H-B groups in the open face of the B, cluster: in solution, the llB(28.87 MHz) and lH(220 MHz) n.m.r. spectra indicate pseudo-threefold symmetry with nine terminal B-H bonds and five more labile hydrogen atoms.THE structure of the BgH14-anion has been predicted1 on the basis of the known structure of the isoelectronic adduct MeCNB,H13, but no definitive evidence has been presented for its structure, although n.m.r. data have been reported., This paper gives the results of a single-crystal X-ray structure determination of CsB,H14 and relates this to the UB and 1H n.m.r. spectra of the B9H14-anion in various solvents over a range of temperature.

The crystal and molecular parameters of cesium tetrachlorocuprate have been refined using an X-ray diffraction intensity data set. The crystal system is orthorhombic, space group Pnam, with four formula weights per unit cell; the unit cell parameters are a = 9.7599 ( 12), b = 12.3967 (12), and c = 7.6091 (9) A. A total of 1786 independent reflections were used in least-squares refinement of the molecular parameters, leading to a final R factor (on F) of 5.5%. The anion has crystallographically imposed m symmetry and the three independent copper-chlorine bond lengths are 2.244 (4), 2.235 (4), and 2.220 (3) A. The crystal forces acting upon the bonds within the anion were calculated, and after correction for their effects and for thermal motion the copper-chlorine bond length in an isolated anion is 2.283 A. The charge distribution within the anion is estimated to be [Cu°60-(3) (a) M.