The structure of aqua-hydroxo double salts

The preparation and structure of two so-called aqua-hydroxo double salts of cobalt(III) are reported. X-ray structural analysis showed the compounds not to be double salts of two distinct mononuclear cations but to contain one binuclear cation in which the two equivalent cobalt atoms are bridged by a hydrogen oxide ligand (μ-H₃O₂). Compound 1, trans-{[Co(en)₂NO₂]₂(H₃O₂)}(C1O₄)₃·2H₂O forms monoclinic crystals, space group P2₁/n, with a = 12.098(2) Å, b = 8.981(1) Å, c = 14.415(2) Å, β = 93.39(2)°, V = 1563(1) ų and Z = 2. Compound 2, trans-{[Co(en)₂NCS]₂(H₃O₂)}(CF₃SO₃)₃·H₂O forms triclinic crystals, space group P1 with a = 12.864(2) Å, b = 14.429(2) Å, c = 11. 177(1) Å, α = 105.21(3)°, β = 100.33(2)°, γ = 65.96(2)°, V = 1822(1) ų and Z = 2. The two structures were refined by least-squares methods to residuals of R = 0.077, R_w = 0.087 and R = 0.063, R_w = 0.069, respectively. In 1, the dimer resides on a crystallographic inversion center and the O⋯O separation in the H₃O₂ bridge is 2.412(9) Å. In 2 there is no crystallographic symmetry imposed upon the dimer but the two CoO(H₃O₂) distances are identical within the experimental error. The O⋯O length in the H₃O₂ unit is 2.415(6) Å.