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Ab initio SCF molecular orbital calculations have been performed on the free Cu(OH2)62+ complex in D2h symmetry. Two extrema in the adiabatic electron energy potential surface were obtained corresponding to a tetragonal distortion from the regular Th symmetry of the octahedral complex, as expected from the Jahn-Teller theorem in a case with strong E-e type vibronic coupling. The tetragonally elongated octahedral structure with Cu-20ax at 2.25 AA and Cu-40eq at 2.06 AA gave a slightly lower energy (72 cm-1) than the compressed geometry with Cu-20ax at 2.02 AA and Cu-40eq at 2.17 AA. The calculated Jahn-Teller energy is 650 cm-1 from that of the regular Th symmetry with Cu-60 at 2.115 AA. EXAFS measurements were performed on aqueous Cu2+ solutions and showed a greater distortion with Cu-40eq at 1.99 AA and Cu-20ax at about 2.29 AA. Infrared absorption spectroscopic measurements were made on the O-D stretching vibrations of HDO molecules in aqueous Cu2+ and Ni2+ solutions with added D2O in order to study the hydrogen bonds from the hydrated ions. A distorted Cu(OH2)62+ ion is expected to form hydrogen bonds of unequal strength because of the stronger polarisation of the more strongly bonded equatorial water molecules. Two bands ascribed to the hydration of the Cu2+ ion were obtained, the more intense corresponding to the strongest hydrogen bonds at approximately=2400 cm-1, and the weaker at approximately=2530 cm-1, whereas for Ni2+ only one band at approximately=2420 cm-1 was found. With the use of a correlation between RO...O versus nu OD from crystal structure data the mean hydrogen-bonded O...O distances to the second hydration shell are estimated to about 2.74 AA from the equatorial water molecules and 2.88 AA from the axial. The IR data show that the distortions induced by the Jahn-Teller effect on the second hydration sphere are visible on a vibrational timescale, despite the fast intramolecular inversion of the distortion axis between the three principal octahedral directions. The splitting of the nu OD bands in the Tutton salts Cs2(M(OH2)6)(SO4)2, M=Cu or Ni, with some added D2O has also been measured and compared to crystal structure data of the hydrogen bonded distances. The separation of about 107 cm-1 between the two groups of O-D stretching vibrations found in the Cu salt can be ascribed to a static Jahn-Teller effect.

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A full-matrix least-squares refinement using Jost's 1961 data reduced R(hkl) for 760 reflexions to 0.076.The refined bond lengths of the (PO3)~ chain, P-O (bridge) 1.610 and P-O (terminal) 1.479/~, agree with results for (RbPO3)z.The crystal structure of sodium Kurrol salt, type A, a polyphosphate of composition (NaPO3)z, was determined by Jost (1961). The structure was then refined by means of difference syntheses using only hOl and hkO data, although sign determination was carried out by direct methods for the layers hll to h51 also. The present three-dimensional refinement by least squares uses all the data except the separate hkO reflexions, which are probably more affected by absorption than the others. No absorption corrections were applied.Of a possible 1000 reflexions in the layers hOl to h51 (ca. 60% of the Cu sphere), 760 were observed. The starting point of the new refinement, which was carried out (in Glasgow) with the full-matrix leastsquares program of Smith and Cruickshank, was the set of atomic coordinates and isotropic vibrational parameters from the earlier refinement. Atomic form factors for neutral atoms were taken from International Tables for X-ray Crystallography (1962). The weighting scheme used was of the form Vw= ([1 --exp (-PI( sin20)/22)]where the constants took the final values P1=500, 1°2=0.01, P3=0.001 and P4=0.00001. Initially, atomic coordinates, isotropic vibrational parameters and layer scale factors were refined. After three cycles, the vibrational parameters were allowed to vary anisotropically, with the layer scale factors, but not the overall scale factor, held constant at their converged values. Complete convergence was attained in six more cycles; final R(hkl) =0.076 for the 760 observed reflexions. A final difference synthesis showed no peaks over 1 e./~ -3. Librational corrections were considered, but are of rather dubious value in an infinite chain structure; however, calculations based on the P207 group and individual PO4 tetrahedra were carried out; the results, which gave corrections of less than a half an e.s.d., were not applied. The final atomic coordinates, vibrational parameters and their e.s.d, are given in Table 1.