Potassium aquaterbium(III) oxalate sulfate

Single crystals of KTb(C2O4)(SO4)(H2O), potassium aquaterbium(III) oxalate sulfate, were obtained under hydrothermal conditions. In the crystal structure, the Tb(III) atom is coordinated by four O atoms from two oxalate anions, three O atoms from three sulfate anions and one O atom from a water molecule within a TbO8 distorted square antiprismatic coordination. The potassium and terbium(III) atoms are bridged by the oxalate and sulfate groups, forming a three-dimensional structure. The coordination mode of the oxalate has not yet been reported. O—H⋯O hydrogen bonding between the water molecules and the oxygen atoms of oxalate and sulfate anions is also observed.


S1. Comment
Recently, rationally design of novel inorganic componds based on alkali metal ions and rare earth ions are currently of great interest because of their potential applications in photoluminescent fields. For purpose of enriching the chemistry field of this compound family, we have successfully synthesized the title compound.
In the title compound, the coordination environments of the rare earth Tb III cations consist of eight O atoms which are associated with one water molecule, two sulfate groups and two oxalates. Tb III cations are at the shared apex of two dicapped rectangular pyramids (Fig.1) Oxalates are of considerable interest because many of them are natural minerals and in addition, the oxalate anion can adopt different coordination modes to bind metals to form infinite chains, sheets and networks, leading to the rich structural chemistry (Lu et al., 2004;Dean et al., 2004;Audebrand et al., 2003). In the title compound, the oxalate ligand has an unique coordination mode (κ 3 -κ 2 -µ 4 )-(κ 3 -κ 2 -µ 4 )-µ 6 -ox 2-. Fig.2 shows coordination mode of the oxalate and sulfate ligands in the title compuond.
Two adjacent Tb III ions were connected through the oxalates to form one-dimensional chain structure (see Fig.3), and then were connected through the sulfate anions and water molecules to form the three-dimensional framework (see Fig.4).

S2. Experimental
A mixture of FeSO 4 .7H 2 O (0.1 mmol),Tb(NO 3 ) 3 .5H 2 O (0.1 mmol) and oxalic acid (0.2 mmol) in H 2 O (10 mL) was adjust to pH=6.8 with KOH aqueous solution, sealed in a 25 mL Teflon-lined bomb at 430 K for 4 days and then slowly cooled to room temperature at a rate of 5° K per hour. Colorless block crystals were obtained by filtration.The structure was determined by single-crystal diffraction.

S3. Refinement
Water H atoms were located in a difference Fourier maps and refined to restraint with O-H distance of 0.97Å and Uĩso(H) = 1.2Ueq(O). In order improve the R and wR factors,weak diffraction reflections in high 2 theta angles were omitted.Because of difficulties in obtaining convergence in the refinement the anisotropy of the atomic displacement parameters of some O and C atoms were restrained.

Figure 1
A view of the environment of (a) the Tb atom, The symmetry codes are in Table 1.Displacement ellipsoids are drawn at the 50% probability level.    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 R-factors(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.