A model for trivalent actinides in media containing high carbonate concentrations - Structural characterization of the lanthanide tetracarbonate [Co(NH3)(6)][Na(mu-H2O)(H2O)(4)](2)[Ho(CO3)(4)]center dot 4H(2)O

The identity of the limiting Ho-III species in aqueous solutions with high carbonate concentrations has been determined to be Ho(CO3)(4)(5-). Single c rystals of [Co(NH3)(6)][Na(mu -H2O)(H2O)(4)](2)[Ho(CO3)(4)]. 4H(2)O were ob tained by the addition of [Co(NH3)(6)](3+) to an aqueous 0.04 m solution of Ho-III in 2.1 M Na2CO3. The asymmetric unit contains the anion, [Ho(CO3)(4 )](5-), a [Co(NH3)(6)](3+) cation and two Na+ cations, which are bound to H 2O molecules in an edge-sharing bioctahedral geometry. The [Ho(CO3)(4)](5-) anion is eight coordinate with four bidentate carbonate ligands bound to t he Ho atom. The molecule has essentially C-2 nu symmetry with two coplanar carbonates making a vane, which is perpendicular to a similar vane produced by the other two carbonate ligands. An alternative way to this view molecu le is through the geometry of the C atoms, which are found in a distorted t etrahedron. The average Ho-O distance was determined to be 2.361(5) Angstro m, while the average Ho-C distance was 2.784(6) A. The IR and Raman spectra were determined in both the solid state and solution in order to confirm t he solution speciation. The Raman data show a single CO32- stretch for the solid at 1062 cm(-1), The solution data show multiple peaks with the most p rominent being at 1048 cm(-1), which is consistent with the literature repo rts of an equilibrium mixture. The IR data for the solids confirm the X-ray results showing bidentate carbonate ligands by the splitting of the nu (3) band of the CO32-. The crystal data for [Co(NH3)(6)][Na(mu -H2O)(H2O)(4)]( 2)[Ho(Co-3)(4)]. 4H(2)O are as follows: monoclinic space group P2/n, a = 8. 7091(5) Angstrom, b = 10.8744(6) Angstrom, c = 15.7971(9) Angstrom, beta = 93.117(1)degrees, Z = 2, R1 = 0.0307, wR2 = 0.0756.