Redetermination of [EuCl2(H2O)6]Cl

The crystal structure of the title compound, hexaaquadichloridoeuropium(III) chloride, was redetermined with modern crystallographic methods. In comparison with the previous study [Lepert et al. (1983 ▶). Aust. J. Chem. 36, 477–482], it could be shown that the atomic coordinates of some O atoms had been confused and now were corrected. Moreover, it was possible to freely refine the positions of the H atoms and thus to improve the accurracy of the crystal structure. [EuCl2(H2O)6]Cl crystallizes with the GdCl3·6H2O structure-type, exhibiting discrete [EuCl2(H2O)6]+ cations as the main building blocks. The main blocks are linked with isolated chloride anions via O—H⋯Cl hydrogen bonds into a three-dimensional framework. The Eu3+ cation is located on a twofold rotation axis and is coordinated in the form of a Cl2O6 square antiprism. One chloride anion coordinates directly to Eu3+, whereas the other chloride anion, situated on a twofold rotation axis, is hydrogen bonded to six octahedrally arranged water molecules.

The crystal structure of the title compound, hexaaquadichloridoeuropium(III) chloride, was redetermined with modern crystallographic methods. In comparison with the previous study [Lepert et al. (1983). Aust. J. Chem. 36,[477][478][479][480][481][482], it could be shown that the atomic coordinates of some O atoms had been confused and now were corrected. Moreover, it was possible to freely refine the positions of the H atoms and thus to improve the accurracy of the crystal structure.
[EuCl 2 (H 2 O) 6 ]Cl crystallizes with the GdCl 3 Á6H 2 O structuretype, exhibiting discrete [EuCl 2 (H 2 O) 6 ] + cations as the main building blocks. The main blocks are linked with isolated chloride anions via O-HÁ Á ÁCl hydrogen bonds into a threedimensional framework. The Eu 3+ cation is located on a twofold rotation axis and is coordinated in the form of a Cl 2 O 6 square antiprism. One chloride anion coordinates directly to Eu 3+ , whereas the other chloride anion, situated on a twofold rotation axis, is hydrogen bonded to six octahedrally arranged water molecules.
Supporting information for this paper is available from the IUCr electronic archives (Reference: WM5012).

Experimental
The title compound was obtained by adding small portions of commercially

Refinement
The positions of all hydrogen atoms were identified from the difference Fourier map and were freely refined, applying one common isotropic displacement parameter to all six H atoms.
For better comparability of our structure model with the previous model by Lepert et al. (1983) we haved used the same setting in space group P2/n. In the crystal structure description given by Lepert et al. (1983) several misspellings of the atomic positions were adopted into the databases. The published model leads to diverging refinements if taken as starting values. We have analysed the misspellings and give a conclusive assignment of the atomic positions. If standardized by the program STRUCTURE-TIDY (Gelato & Parthé, 1987), the comparison of our model with the one given by Lepert et  al. (1983) shows, in addition to an origin shift of (0, 1/2, 0), that the y and z coordinates of atoms O1, O2 and O3 were permutated. In fact, y(O1) and z(O1) belong to y(O3) and z(O3), y(O2) and z(O2) belong to y(O1) and z(O1), and finally y(O3) and z(O3) belong to y(O2) and z(O2). If re-ordered in the given way, the refinement based on starting values from Lepert et al. (1983) lead to convergence in few cycles with satisfying results.

Figure 1
The cationic [Eu(H 2 O) 6 Cl 2 ] + unit in [Eu(H 2 O) 6 Cl 2 ]Cl. Ellipsoids are drawn at 75% probability level. Hydrogen atoms are drawn as small black spheres with arbitrary radius. [Symmetry code: (i) 3/2 -x, y, 1/2 -z; (ii) x, y, -1 + z; (iii) 3/2 -x, y,    The coordination sphere of the coordinating Cl1 atom is a distorted tetrahedron built from three water molecules and one europium atom. The water molecules coordinate via hydrogen bonds. [Symmetry codes: (i) 1 -x, -y, 1 -z; (ii) 1/2 + x, 1y, 1/2 + z; (iii) 3/2 -x, y 3/2 -z; (iv) x, y, 1 + z.]  The coordination sphere of the anionic Cl2 atom consists of six water molecules coordinating via their hydrogen atoms forming a distorted octahedron. [Symmetry codes: (i) 3/2 -x, y, 1/2 -z; (ii) x, y, 1 + z; (iii) 3/2 -x, 1 + y, 3/2 -z; (iv) x, 1 + y, z; (v) 1 -x, 1 -y, 1 -z; (vi) 1/2 + x, 1 -y, 1/2 + z.] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.63 e Å −3 Δρ min = −0.77 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.