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.

Related literature

For previous structure determinations of the title compound, see: Lepert et al. (1983); Bel'skii & Struchkov (1965). For the GdCl₃·6H₂O structure type and isotypic compounds, see: Marezio et al. (1961); Bell & Smith (1990); Burns & Peterson (1971); Graeber et al. (1966); Habenschuss & Spedding (1980); Hoch & Simon (2008); Junk et al. (1999); Reuter et al. (1994). For related structures, see: Demyanets et al. (1974); Reuter et al. (1994). For standardization of crystal data, see: Gelato & Parthé (1987).

Experimental

Crystal data

• [EuCl₂(H₂O)₆]Cl

• M_r = 366.41

• Monoclinic, P 2/n

• a = 9.6438 (12) Å

• b = 6.5322 (10) Å

• c = 7.929 (3) Å

• β = 93.653 (13)°

• V = 498.4 (2) ų

• Z = 2

• Ag Kα radiation

• λ = 0.56083 Å

• μ = 3.74 mm⁻¹

• T = 293 K

• 0.23 × 0.20 × 0.18 mm

Data collection

• Stoe IPDS I diffractometer

• Absorption correction: multi-scan (MulScanAbs in PLATON; Spek, 2009) T_min = 0.425, T_max = 0.510

• 13401 measured reflections

• 1762 independent reflections

• 1653 reflections with I > 2σ(I)

• R_int = 0.043

Refinement

• R[F² > 2σ(F²)] = 0.015

• wR(F²) = 0.032

• S = 1.03

• 1762 reflections

• 66 parameters

• All H-atom parameters refined

• Δρ_max = 0.63 e Å⁻³

• Δρ_min = −0.77 e Å⁻³

Table 1
Selected bond lengths (Å)

Eu1—O1	2.4618 (15)
Eu1—O2^i	2.4620 (18)
Eu1—O3	2.3078 (16)
Eu1—Cl1^ii	2.7690 (12)
Symmetry codes: (i) x, y, z-1; (ii) -x+1, -y, -z+1.

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯Cl2^i	0.74 (4)	2.36 (4)	3.081 (2)	166.08
O2—H2⋯Cl1^iii	0.81 (3)	2.54 (3)	3.351 (2)	174.97
O2—H3⋯Cl2^iv	0.76 (4)	2.51 (4)	3.2234 (19)	157.37
O3—H4⋯Cl1^i	0.72 (4)	2.35 (4)	3.036 (2)	160.44
O1—H5^v⋯Cl1	0.74 (2)	2.36 (3)	3.095 (2)	173.89
O3—H6⋯Cl2^vi	0.79 (4)	2.53 (4)	3.310 (2)	170.66
Symmetry codes: (i) x, y, z-1; (iii) ; (iv) x, y-1, z; (v) ; (vi) -x+1, -y+1, -z+1.

Data collection: X-AREA (Stoe & Cie, 2006); cell refinement: X-AREA; data reduction: X-AREA; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Crystal Impact, 2007); software used to prepare material for publication: SHELXL97.

Supporting information

S1. Comment

[EuCl₂(H₂O)₆]Cl crystallizes with the GdCl₃^.6H₂O structure type (Marezio et al., 1961), like many metal trichloride hexahydrates MCl₃^.6H₂O with M = Y (Bell & Smith, 1990), Ce (Reuter et al., 1994), Nd (Habenschuss & Spedding, 1980), Sm - Tm (Graeber et al., 1966), Am, Bk (Burns & Peterson, 1971), and three bromide hexahydrates MBr₃^.6H₂O with M = Pr, Dy (Junk et al., 1999) and Eu (Hoch & Simon, 2008). The first structure determination of the title compound was performed on the basis of film data (Bel'skii & Struchkov, 1965) and without determination of the hydrogen atom positions. A first exact structure determination with all atomic positions was performed by Lepert et al. (1983). However, the published data contain errors in the atomic coordinates. We have thus redetermined the structure on the basis of modern area detector data.

The Eu³⁺ cation in [EuCl₂(H₂O)₆]Cl is located on a twofold rotation axis and is coordinated in form of a distorted square antiprism defined by six water molecules and two chloride anions (Fig. 1, Table 1). Hydrogen bonds O—H···Cl connect the [EuCl₂(H₂O)₆]⁺ cations with the Cl^- counter-anions to a three-dimensional framework (Fig 2). The complexing chloride anion Cl1 is surrounded by three, the isolated chloride anion Cl2 by six H atoms (Figs. 3, 4), forming hydrogen bonds with Cl···H distances between 2.36 (4) and 2.54 (3) Å (Table 2) and are in good agreement with those in other chloride hydrates. The Eu^III—O distances in [EuCl₂(H₂O)₆]Cl range from 2.3078 (16) to 2.4620 (18) Å and are comparable with those in EuCl₃^.3H₂O (2.39–2.40 Å; Reuter et al., 1994), EuCl₃^.6H₂O (2.39–2.43 Å; Graeber et al., 1966), or EuCl(OH)₂ (2.35–2.44 Å; Demyanets et al., 1974) and also with those in EuBr₃^.6H₂O (Hoch & Simon, 2008).

Related literature

For previous structure determinations of the title compound, see: Lepert et al. (1983); Bel'skii & Struchkov (1965). For the GdCl₃.6H₂O structure type and isotypic compounds, see: Marezio et al. (1961); Bell & Smith (1990); Burns & Peterson (1971); Graeber et al. (1966); Habenschuss & Spedding (1980); Hoch & Simon (2008); Junk et al. (1999); Reuter et al. (1994). For related structures, see: Demyanets et al. (1974); Reuter et al. (1994). For standardization of crystal data, see: Gelato & Parthé (1987).

S2. Experimental

The title compound was obtained by adding small portions of commercially available Eu₂O₃ (Alfa Aesar, 99.99%) into concentrated aqueous HCl solution at 353 K until only minor amounts of undissolved Eu₂O₃ remained visible for several minutes. The surplus Eu₂O₃ finally was dissolved by dropwise addition of concentrated HCl to the solution until a clear colourless solution was obtained. The solution was allowed to cool to 293 K, yielding colourless single-crystal blocks of [EuCl₂(H₂O)₆]Cl.

S3. 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.

Computing details

Data collection: X-AREA (Stoe & Cie, 2006); cell refinement: X-AREA (Stoe & Cie, 2006); data reduction: X-AREA (Stoe & Cie, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Crystal Impact, 2007); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. The cationic [Eu(H2O)6Cl2]^+ unit in [Eu(H2O)6Cl2]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, 3/2 - z; (iv) 1 - x, -y, 1 - z; (v) 1/2 + x, -y, -1/2 + z.]
	Fig. 2. View along [010] on the crystal structure of [Eu(H2O)6Cl2]Cl. Small black spheres represent H atoms, blue ellipsoids represent Eu atoms, olive ellipsoids represent Cl atoms, turquoise ellipsoids represent O atoms. Grey polyhedra represent the coordination of H atoms around Cl atoms.
	Fig. 3. 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, 1 - y, 1/2 + z; (iii) 3/2 - x, y 3/2 - z; (iv) x, y, 1 + z.]
	Fig. 4. 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.]

Hexaaquadichloridoeuropium(III) chloride

Crystal data

[EuCl2(H2O)6]Cl	Z = 2
Mr = 366.41	F(000) = 348
Monoclinic, P2/n	Dx = 2.441 Mg m^−3
Hall symbol: -P 2yac	Ag Kα radiation, λ = 0.56083 Å
a = 9.6438 (12) Å	Cell parameters from 13548 reflections
b = 6.5322 (10) Å	µ = 3.74 mm^−1
c = 7.929 (3) Å	T = 293 K
β = 93.653 (13)°	Stretched cuboid, clear colourless
V = 498.4 (2) Å^3	0.23 × 0.20 × 0.18 mm

Data collection

Stoe IPDS I diffractometer	1762 independent reflections
Radiation source: fine-focus sealed tube	1653 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.043
ϕ scan	θmax = 25.5°, θmin = 3.0°
Absorption correction: multi-scan (MulScanAbs in PLATON; Spek, 2009)	h = −14→14
Tmin = 0.425, Tmax = 0.510	k = −10→10
13401 measured reflections	l = −11→11

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.015	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.032	All H-atom parameters refined
S = 1.03	w = 1/[σ^2(Fo^2) + (0.015P)^2] where P = (Fo^2 + 2Fc^2)/3
1762 reflections	(Δ/σ)max < 0.001
66 parameters	Δρmax = 0.63 e Å^−3
0 restraints	Δρmin = −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 F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Eu1	0.7500	0.150918 (18)	0.2500	0.01345 (3)
Cl1	0.44156 (5)	0.16532 (7)	0.76010 (6)	0.02588 (9)
Cl2	0.7500	0.62387 (11)	0.7500	0.02813 (13)
O1	0.85427 (18)	0.4256 (2)	0.0872 (2)	0.0275 (3)
O2	0.78164 (18)	0.0484 (2)	0.9561 (2)	0.0263 (3)
O3	0.56055 (17)	0.3002 (2)	0.1060 (2)	0.0278 (3)
H1	0.827 (4)	0.454 (6)	0.001 (5)	0.051 (4)*
H2	0.846 (3)	0.084 (5)	0.902 (4)	0.035 (3)*
H3	0.766 (4)	−0.063 (7)	0.933 (5)	0.058 (5)*
H4	0.551 (4)	0.265 (6)	0.020 (5)	0.052 (5)*
H5	0.881 (4)	0.520 (5)	0.129 (5)	0.040 (3)*
H6	0.491 (4)	0.319 (6)	0.152 (5)	0.044 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Eu1	0.01398 (5)	0.01346 (5)	0.01244 (6)	0.000	−0.00293 (3)	0.000
Cl1	0.02417 (18)	0.02396 (18)	0.0286 (2)	−0.00652 (16)	−0.00541 (16)	0.00198 (17)
Cl2	0.0297 (3)	0.0305 (3)	0.0235 (3)	0.000	−0.0033 (2)	0.000
O1	0.0368 (8)	0.0229 (6)	0.0214 (8)	−0.0100 (6)	−0.0085 (6)	0.0038 (5)
O2	0.0336 (7)	0.0277 (7)	0.0175 (7)	−0.0047 (6)	−0.0001 (6)	−0.0039 (5)
O3	0.0250 (6)	0.0317 (7)	0.0250 (8)	0.0067 (5)	−0.0113 (6)	−0.0028 (5)

Geometric parameters (Å, º)

Eu1—O1	2.4618 (15)	O2—H3	0.76 (4)
Eu1—O1^i	2.4618 (16)	O2—H2	0.81 (3)
Eu1—O2^ii	2.4620 (18)	O3—H4	0.72 (4)
Eu1—O2^iii	2.4620 (18)	O3—H6	0.79 (4)
Eu1—O3	2.3078 (16)	Cl1—H2	2.535 (4)
Eu1—O3^i	2.3078 (15)	Cl1—H4	2.3535 (4)
Eu1—Cl1^iv	2.7690 (12)	Cl1—H5^vi	2.36 (3)
Eu1—Cl1^v	2.7690 (12)	Cl2—H1^i	2.36 (4)
O1—H1	0.74 (4)	Cl2—H3^vii	2.5071 (4)
O1—H5	0.74 (4)	Cl2—H6^viii	2.53 (4)
Eu1—O1—H1	122 (3)	O1—Eu1—O2^ii	67.83 (6)
Eu1—O1—H1	122 (3)	O1^i—Eu1—Cl1^iv	105.35 (5)
Eu1—O1—H5	121 (3)	O1—Eu1—Cl1^iv	145.35 (4)
Eu1—O1—H5	121 (3)	O2^ii—Eu1—O2^iii	148.45 (8)
Eu1^ix—O2—H2	124 (3)	O2^ii—Eu1—Cl1^iv	83.83 (4)
Eu1^ix—O2—H2	124 (3)	O2^iii—Eu1—Cl1^iv	72.65 (4)
Eu1^ix—O2—H3	117 (3)	O3^i—Eu1—O1^i	76.70 (6)
Eu1^ix—O2—H3	117 (3)	O3—Eu1—O1^i	67.31 (6)
Eu1—O3—H4	112 (3)	O3^i—Eu1—O2^ii	116.15 (7)
Eu1—O3—H4	112 (3)	O3—Eu1—O2^ii	77.82 (6)
Eu1—O3—H6	120 (3)	O3^i—Eu1—O3	130.01 (8)
Eu1—O3—H6	120 (3)	O3^i—Eu1—Cl1^iv	146.64 (4)
O1^i—Eu1—O1	86.43 (9)	O3—Eu1—Cl1^iv	78.18 (5)
O1^i—Eu1—O2^ii	140.68 (5)	Cl1^iv—Eu1—Cl1^v	83.51 (2)

Symmetry codes: (i) −x+3/2, y, −z+1/2; (ii) x, y, z−1; (iii) −x+3/2, y, −z+3/2; (iv) −x+1, −y, −z+1; (v) x+1/2, −y, z−1/2; (vi) x−1/2, −y+1, z+1/2; (vii) x, y+1, z; (viii) −x+1, −y+1, −z+1; (ix) x, y, z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···Cl2^ii	0.74 (4)	2.36 (4)	3.081 (2)	166.08
O2—H2···Cl1^iii	0.81 (3)	2.54 (3)	3.351 (2)	174.97
O2—H3···Cl2^x	0.76 (4)	2.51 (4)	3.2234 (19)	157.37
O3—H4···Cl1^ii	0.72 (4)	2.35 (4)	3.036 (2)	160.44
O1—H5^vi···Cl1	0.74 (2)	2.36 (3)	3.095 (2)	173.89
O3—H6···Cl2^viii	0.79 (4)	2.53 (4)	3.310 (2)	170.66

Symmetry codes: (ii) x, y, z−1; (iii) −x+3/2, y, −z+3/2; (vi) x−1/2, −y+1, z+1/2; (viii) −x+1, −y+1, −z+1; (x) x, y−1, z.