Intercalated brucite-type layered cobalt(II) hydroxysulfate

In an attempt to synthesize new cobalt(II) sulfate framework structures using 1,4-diazabicyclo[2.2.2]octane as a template, crystals of poly[0.35-[hexaaquacobalt(II)] [tri-μ-hydroxido-μ-sulfato-dicobalt(II)]], {[Co(H2O)6]0.35[Co2(OH)3(SO4)]}n, were obtained as a mixture with [Co(H2O)6]SO4 crystals. The crystal structure can be described as being constructed from discrete brucite-type [Co4(OH)6(SO4)2] layers, each of which is built up from edge-shared [Co(OH)6] and [Co(OH)4(OSO3)2] octahedra, with partial intercalation by [Co(H2O)6]2+ ions. The absence of ca 30% of the [Co(H2O)6]2+ cations indicates partial oxidation of cobalt(II) to cobalt(III) within the layer.

In an attempt to synthesize new cobalt (II)
Unlike the Co 5 (OH) 6 (SO 4 ) 2 (H 2 O) 4 structure, the sulfate anion acts as a monodentate ligand and is coordinate covalently connected to the layered Co2 ion via the apical O atom, leaving the three basal O atoms pointing into the interlayered space  (Allen, 2002

Refinement
Hydrogen atoms were located by difference Fourier methods. The positions of these were refined subject to weak bond length restraints. Displacement parameters for the hydrogen atoms were set at 1.5 times the isotropic diaplcement parameter of the oxygen atom.
Prior to the refinement of site ocupancy of [Co(H 2 O) 6 ] 2+ , all atoms were located using Fourier difference methods.
The displacement parameters of the intercalating ion were anomalously large. There were large maxima and minima in the residual electron density: e-max = 2.59 e Å -3 (centered on Co2); e-min = -2.58 e Å -3 . At this stage wR(F 2 ) = 0.1914.

Refinement of the occupancy of the [Co(H 2 O) 6 ] 2+ cation resulted in a significant improvement in the quality of the fit
to the data: e-max = 1.044 e Å -3 ; e-min = -1.046 e Å -3 and wR(F 2 ) = 0.132.
Careful inspection of the diffraction images did not reveal any weak reflections which might indicate ordering of the partially occupied cation. Fig. 1

Special details
Geometry. All e.s. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.