STRUCTURE OF HEXAAQUACOPPER(II) BROMATE

[Cu(H2O)6](BrO3)2, M(r) = 427.44, cubic, Pa3BAR, a = 10.3240 (6) angstrom, V = 1100.38 (4) angstrom 3, Z = 4, D(x) = 2.580 g cm-3, lambda(Mo K-alphaBAR) = 0.71073 angstrom, mu = 92.32 cm-1, F(000) = 828, T = 296 K, R = 0.038 for 336 unique reflections having I > sigma-I. The single type of copper ion (site symmetry 3BAR) is coordinated by six water-molecule O atoms, each at an observed distance of 2.079 (4) angstrom, in an array which is virtually regular octahedral, the nominal 90-degrees angles measuring 89.95 (15) and 90.05 (15)-degrees. Thus, this is not a typical Cu(II) complex in which (consistent with a static Jahn-Teller effect) a distorted octahedral array displays '(2 + 2 + 2)' coordination; rather, it is the sixth strict example of a Cu(II) static structure inconsistent with the Jahn-Teller theorem. The presence of a dynamic Jahn-Teller effect is supported by the data. The single type of bromate ion has an observed Br-O bond length 1.649 (3) angstrom and O-Br-O bond angle 104.17 (15)-degrees. The bromate ion was found to manifest rigid-body behavior but, consistent with a dynamic Jahn-Teller effect, the copper-oxygen complex did not. The Br-O bond length corrected for rigid-body motion is 1.663 angstrom. Refinement of the positional parameters of the two inequivalent H atoms permitted a detailed analysis of hydrogen bonding, which occurs principally between the oxygen octahedra and the bromate groups. This structure is isomorphic with those of hexaaquanickel(II) chlorate, hexaaquacobalt(II) bromate and hexaaquanickel(II) bromate, all of which have been reported recently from this laboratory. It is of interest that a tetrahydrated phase crystallized at room temperature from a saturated aqueous copper(II) chlorate solution, whereas a hexahydrated phase crystallized from a saturated aqueous copper(II) bromate solution treated in the same manner.