Redetermination of the Tutton's salt Cs₂[Cu(H₂O)₆](SO₄)₂

The crystal structure of dicaesium hexa­aqua­copper(II) bis­[sulfate­(VI)], Cs₂[Cu(H₂O)₆](SO₄)₂, has been redetermined from single-crystal X-ray diffraction data. In comparison with the previous refinement based on single-crystal neutron data [Shields & Kennard (1972). Cryst. Struct. Commun. 1, 189–191], the results show an improved precision and benefit from inclusion of anisotropic displacement parameters for the non-H atoms. The structure is characterized by a mean Cu—O bond length of 2.094 Å. The [Cu(H₂O)₆] octa­hedron ( symmetry) is strongly distorted because of the Jahn–Teller effect, with a calculated distortion parameter Δ of 0.0054. The Cs⁺ cation is ninefold coordinated by seven O atoms and two water mol­ecules, with a mean Cs—O bond length of 3.238 Å.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](S-O) = 0.003 Å
• R factor = 0.034
• wR factor = 0.080
• Data-to-parameter ratio = 29.4

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT061_ALERT_3_B Tmax/Tmin Range Test RR' too Large .............       0.70

Alert level C
ABSTM02_ALERT_3_C  The ratio of expected to reported Tmax/Tmin(RR') is < 0.90
            Tmin and Tmax reported:      0.226     0.584
            Tmin(prime) and Tmax expected:      0.123     0.259
            RR(prime) =      0.812
            Please check that your absorption correction is appropriate.
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       0.44
PLAT068_ALERT_1_C Reported F000 Differs from Calcd (or Missing)...          ?
PLAT128_ALERT_4_C Non-standard setting of Space group P21/c   ....    P21/a
PLAT354_ALERT_3_C Short   O-H Bond (0.82A)   OW3    -   H32    ...       0.71 Ang.
PLAT720_ALERT_4_C Number of Unusual/Non-Standard Label(s) ........          3

Alert level G
ABSTM02_ALERT_3_G  When printed, the submitted absorption T values will be
            replaced by the scaled T values. Since the ratio of scaled T's
            is identical to the ratio of reported T values, the scaling
            does not imply a change to the absorption corrections used in
            the study.
            Ratio of Tmax expected/reported      0.443
            Tmax scaled      0.259 Tmin scaled      0.100
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K
PLAT794_ALERT_5_G Check Predicted Bond Valency for Cu          (2)       2.11

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   6 ALERT level C = Check and explain
   4 ALERT level G = General alerts; check

   3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   4 ALERT type 3 Indicator that the structure quality may be low
   3 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

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S1. Comment

The title compound Cs₂[Cu(H₂O)₆](SO₄)₂ is a member of the isotypic series known as Tutton's salts. Their general formula is M^I₂[M^II(H₂O)₆](XO₄)₂, where M^I and M^II are, respectively, a monovalent and a divalent cation and X is hexavalent S, Se or Cr. The structure of Tutton's salts consists of isolated [M^II(H₂O)₆] octahedra and XO₄^2- tetrahedra connected by the M^I cation (Fig. 1). As a result sheets parallel to (100) are formed, interconnected via medium to weak hydrogen bonds originating from the aqua ligands of the M^II cations to the acceptors of the sulfate groups.

The structure of the title compound has been previously determined by Shields & Kennard (1972) from single-crystal neutron data. However, the original data were characterized by large standard uncertainties of cell parameters and fractional coordinates. Moreover, no displacement parameters were reported. Because of the requirements of accurate structural data to rationalize the crystal chemistry of Tutton's salts, we decided to carry out a redetermination of the crystal structure of Cs₂[Cu(H₂O)₆](SO₄)₂ based on single-crystal X-ray data. The refined cell parameters and the cell volume differ significantly from the reference data [P2₁/a, a = 9.42 (1), b = 12.785 (9), c = 6.28 (1) Å, β = 105.9 (1) °, (Shields & Kennard, 1972)]. The sulfate group is slightly distorted and, similarly to all Tutton's salts, the S—O2 distance is smaller (1.463 (2) Å) than the remaining three S—O distances (1.474 (2)–1.484 (2) Å) because of bond-valence requirements. The mean Cu—O distance of the [Cu(H₂O)₆] octahedron is 2.094 Å. This value compares favourably with the range between 2.085 and 2.098 Å as reported for other M^I₂[Cu(H₂O)₆](SO₄)₂ salts (NH₄: Cotton et al., 1993; K: Simmons et al., 2006; Rb: Ballirano & Belardi, 2007). The [Cu(H₂O)₆] octahedron is strongly distorted as a result of the Jahn-Teller effect. The calculated distortion parameter Δ, as defined by Brown & Shannon (1973), amounts to 0.0054. The Cs⁺ cation is coordinated by seven O atoms and two water molecules with a mean Cs—O distance of 3.238 Å. The refined hydrogen atom positions are not defined with high accuracy. However, after value normalization following the procedure given by Jeffrey & Lewis (1978) and Taylor & Kennard (1983), reasonable H···O distances in the range between 1.765 and 1.850 Å were obtained. Both O1 and O2 atoms are acceptors of a single hydrogen bond, whereas O3 and O4 are acceptors of two hydrogen bonds. As a result, a shortening of the distances H32···O1 and of S—O2 is observed.

Related literature

For related structures of other M^I₂[Cu(H₂O)₆](SO₄)₂ salts, see: Cotton et al. (1993) (M = NH₄); Simmons et al. (2006) (M = K); Ballirano & Belardi (2007) (M = Rb). The distortion of the [Cu(H₂O)₆] octahedron was calculated according to Brown & Shannon (1973). A reasonable hydrogen-bonding geometry was obtained after value normalization following the procedure described by Jeffrey & Lewis (1978) and Taylor & Kennard (1983).

S2. Experimental

The title compound has been prepared by dissolving Cs₂SO₄ (Carlo Erba, P·P·A.) and CuSO₄^.5H₂O (Carlo Erba, P·P·A.) in double deionized water and subsequent slow evaporation of the solvent at 295 K. The obtained crystals, in equilibrium with the mother solution, were removed by filtration and dried at room temperature. The product consisted of platy blue crystals of Cs₂[Cu(H₂O)₆](SO₄)₂.

S3. Refinement

The structure was refined in the non-standard setting P2₁/a of space group P2₁/c for a better comparison with other Tutton's salts. After a few refinement cycles using neutral scattering factors, fully ionized for Cu and half ionized for O and neutral scattering factors for the remaining atoms were finally selected, leading to the lowest R agreement indices. The coordinates of the hydrogen atoms were refined freely using a common U_iso parameter of 0.05 Ų. The deepest hole and the highest peak are, respectively, 0.69 and 0.75 Å from atom Cs.

Computing details

Data collection: XSCANS (Siemens, 1994); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 2003); software used to prepare material for publication: PARST (Nardelli, 1982) and publCIF (Westrip, 2007).

Figures

Fig. 1. The crystal structure of Cs2[Cu(H2O)6](SO4)2 in polyhedral representation, projected along [001].

Dicaesium hexaaquacopper(II) bis[sulfate(VI)]

Crystal data

Cs2[Cu(H2O)6](SO4)2	F(000) = 613.8
Mr = 629.61	Non-standard setting of space group P21/c to adhere to reference data of other Tutton's salts
Monoclinic, P21/a	Dx = 2.864 Mg m^−3
Hall symbol: -P 2yab	Mo Kα radiation, λ = 0.71073 Å
a = 9.4383 (6) Å	Cell parameters from 58 reflections
b = 12.7605 (12) Å	θ = 4.0–22.5°
c = 6.3130 (6) Å	µ = 6.76 mm^−1
β = 106.199 (7)°	T = 293 K
V = 730.14 (11) Å^3	Plate, blue
Z = 2	0.30 × 0.20 × 0.20 mm

Data collection

Siemens P4 diffractometer	2728 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.031
Graphite monochromator	θmax = 35.0°, θmin = 2.8°
ω scans	h = −15→14
Absorption correction: ψ scan (North et al., 1968)	k = 0→20
Tmin = 0.226, Tmax = 0.584	l = 0→10
3436 measured reflections	3 standard reflections every 47 reflections
3208 independent reflections	intensity decay: 1%

Refinement

Refinement on F^2	0 constraints
Least-squares matrix: full	Only H-atom coordinates refined
R[F^2 > 2σ(F^2)] = 0.034	w = 1/[σ^2(Fo^2) + (0.0466P)^2 + 0.5369P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.081	(Δ/σ)max = 0.001
S = 1.09	Δρmax = 1.53 e Å^−3
3208 reflections	Δρmin = −2.57 e Å^−3
109 parameters	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.080 (2)

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
Cu	0.0000	0.0000	0.0000	0.01692 (10)
Cs	0.11407 (2)	0.354561 (15)	0.35562 (3)	0.02654 (8)
S	0.37975 (7)	0.14584 (5)	0.73909 (10)	0.01703 (11)
O1	0.3992 (3)	0.24027 (18)	0.6156 (4)	0.0273 (4)
O2	0.5138 (3)	0.0821 (2)	0.7893 (5)	0.0314 (5)
O3	0.2560 (2)	0.08353 (19)	0.6000 (3)	0.0250 (4)
O4	0.3439 (3)	0.1767 (2)	0.9448 (4)	0.0280 (4)
OW1	0.1450 (3)	0.1085 (2)	0.1577 (4)	0.0252 (4)
OW2	−0.1908 (3)	0.1109 (2)	0.0139 (4)	0.0297 (5)
OW3	−0.0002 (2)	−0.06342 (18)	0.2836 (3)	0.0205 (3)
H11	0.184 (7)	0.093 (5)	0.277 (11)	0.050*
H12	0.199 (7)	0.122 (5)	0.094 (11)	0.050*
H21	−0.281 (7)	0.099 (5)	−0.063 (10)	0.050*
H22	−0.181 (7)	0.166 (5)	−0.017 (11)	0.050*
H31	−0.071 (7)	−0.051 (5)	0.310 (11)	0.050*
H32	0.034 (7)	−0.113 (5)	0.308 (10)	0.050*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu	0.01750 (19)	0.0183 (2)	0.01490 (17)	−0.00407 (15)	0.00436 (13)	0.00055 (14)
Cs	0.02807 (11)	0.02663 (11)	0.02645 (10)	0.00196 (6)	0.01012 (7)	0.00193 (6)
S	0.0157 (2)	0.0182 (2)	0.0169 (2)	−0.00196 (19)	0.00399 (18)	0.00030 (19)
O1	0.0344 (11)	0.0214 (9)	0.0283 (10)	−0.0026 (8)	0.0124 (9)	0.0051 (8)
O2	0.0188 (9)	0.0314 (12)	0.0407 (12)	0.0036 (8)	0.0031 (8)	0.0038 (10)
O3	0.0203 (8)	0.0315 (11)	0.0219 (8)	−0.0090 (8)	0.0039 (7)	−0.0048 (8)
O4	0.0334 (11)	0.0330 (11)	0.0197 (8)	−0.0064 (9)	0.0112 (8)	−0.0049 (8)
OW1	0.0259 (10)	0.0295 (11)	0.0197 (8)	−0.0102 (8)	0.0055 (7)	−0.0012 (7)
OW2	0.0231 (10)	0.0280 (11)	0.0390 (12)	0.0030 (9)	0.0101 (9)	0.0051 (10)
OW3	0.0218 (9)	0.0220 (9)	0.0197 (8)	0.0005 (7)	0.0089 (7)	0.0030 (7)

Geometric parameters (Å, º)

Cu—OW3	1.965 (2)	S—O1	1.474 (2)
Cu—OW3^i	1.965 (2)	S—O3	1.482 (2)
Cu—OW1	2.005 (2)	S—O4	1.484 (2)
Cu—OW1^i	2.005 (2)	S—Cs^v	3.7066 (7)
Cu—OW2^i	2.311 (2)	S—Cs^vi	3.7677 (7)
Cu—OW2	2.311 (2)	S—Cs^vii	3.9035 (8)
Cs—O1	3.098 (2)	O1—Cs^v	3.182 (2)
Cs—O4^ii	3.114 (2)	O2—Cs^vi	3.179 (3)
Cs—O3^iii	3.151 (3)	O2—Cs^v	3.239 (3)
Cs—O2^iii	3.179 (3)	O2—Cs^vii	3.528 (3)
Cs—O1^iv	3.182 (2)	O3—Cs^vi	3.151 (3)
Cs—OW2^v	3.233 (3)	O4—Cs^vii	3.114 (2)
Cs—O2^iv	3.239 (3)	OW1—H11	0.77 (7)
Cs—OW1	3.422 (3)	OW1—H12	0.76 (7)
Cs—O2^ii	3.528 (3)	OW2—Cs^iv	3.233 (3)
Cs—S^iv	3.7066 (7)	OW2—H21	0.87 (7)
Cs—S^iii	3.7677 (7)	OW2—H22	0.74 (6)
Cs—S^ii	3.9035 (8)	OW3—H31	0.75 (7)
Cs—H11	3.47 (6)	OW3—H32	0.70 (7)
S—O2	1.463 (2)
OW3—Cu—OW3^i	180.00 (17)	O2^iv—Cs—OW1	127.78 (6)
OW3—Cu—OW1	90.34 (9)	O1—Cs—O2^ii	126.34 (6)
OW3^i—Cu—OW1	89.66 (9)	O4^ii—Cs—O2^ii	42.23 (6)
OW3—Cu—OW1^i	89.66 (9)	O3^iii—Cs—O2^ii	82.25 (6)
OW3^i—Cu—OW1^i	90.34 (9)	O2^iii—Cs—O2^ii	61.70 (8)
OW1—Cu—OW1^i	180.00 (16)	O1^iv—Cs—O2^ii	125.49 (6)
OW3—Cu—OW2^i	88.94 (9)	OW2^v—Cs—O2^ii	48.26 (6)
OW3^i—Cu—OW2^i	91.06 (9)	O2^iv—Cs—O2^ii	137.77 (8)
OW1—Cu—OW2^i	90.60 (10)	OW1—Cs—O2^ii	82.32 (6)
OW1^i—Cu—OW2^i	89.40 (10)	O2—S—O1	109.96 (15)
OW3—Cu—OW2	91.06 (9)	O2—S—O3	108.73 (15)
OW3^i—Cu—OW2	88.94 (9)	O1—S—O3	108.61 (14)
OW1—Cu—OW2	89.40 (10)	O2—S—O4	110.66 (16)
OW1^i—Cu—OW2	90.60 (10)	O1—S—O4	109.77 (14)
OW2^i—Cu—OW2	180.00 (17)	O3—S—O4	109.07 (13)
O1—Cs—O4^ii	140.29 (7)	S—O1—Cs	116.54 (12)
O1—Cs—O3^iii	97.49 (6)	S—O1—Cs^v	98.82 (11)
O4^ii—Cs—O3^iii	113.63 (6)	Cs—O1—Cs^v	119.34 (7)
O1—Cs—O2^iii	141.84 (6)	S—O2—Cs^vi	102.10 (12)
O4^ii—Cs—O2^iii	73.76 (6)	S—O2—Cs^v	96.71 (12)
O3^iii—Cs—O2^iii	44.43 (6)	Cs^vi—O2—Cs^v	99.31 (8)
O1—Cs—O1^iv	97.59 (5)	S—O2—Cs^vii	93.62 (13)
O4^ii—Cs—O1^iv	83.64 (6)	Cs^vi—O2—Cs^vii	118.30 (8)
O3^iii—Cs—O1^iv	126.51 (6)	Cs^v—O2—Cs^vii	137.77 (8)
O2^iii—Cs—O1^iv	104.49 (6)	S—O3—Cs^vi	102.83 (11)
O1—Cs—OW2^v	81.11 (6)	S—O4—Cs^vii	111.17 (13)
O4^ii—Cs—OW2^v	87.04 (6)	Cu—OW1—Cs	134.36 (11)
O3^iii—Cs—OW2^v	69.69 (6)	Cu—OW1—H11	113 (5)
O2^iii—Cs—OW2^v	85.68 (7)	Cs—OW1—H11	87 (5)
O1^iv—Cs—OW2^v	163.61 (6)	Cu—OW1—H12	112 (5)
O1—Cs—O2^iv	94.88 (6)	Cs—OW1—H12	97 (5)
O4^ii—Cs—O2^iv	111.81 (6)	H11—OW1—H12	112 (6)
O3^iii—Cs—O2^iv	83.77 (6)	Cu—OW2—Cs^iv	134.73 (10)
O2^iii—Cs—O2^iv	80.69 (8)	Cu—OW2—H21	122 (4)
O1^iv—Cs—O2^iv	43.99 (6)	Cs^iv—OW2—H21	75 (4)
OW2^v—Cs—O2^iv	152.24 (6)	Cu—OW2—H22	114 (5)
O1—Cs—OW1	67.15 (6)	Cs^iv—OW2—H22	101 (5)
O4^ii—Cs—OW1	73.24 (6)	H21—OW2—H22	101 (6)
O3^iii—Cs—OW1	144.36 (5)	Cu—OW3—H31	110 (5)
O2^iii—Cs—OW1	142.85 (6)	Cu—OW3—H32	117 (5)
O1^iv—Cs—OW1	88.33 (6)	H31—OW3—H32	122 (7)
OW2^v—Cs—OW1	76.06 (6)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
OW1—H11···O3	0.77 (7)	1.97 (7)	2.714 (2)	166 (7)
OW1—H12···O4^viii	0.75 (7)	1.99 (7)	2.738 (4)	173 (7)
OW2—H21···O2^ix	0.87 (6)	1.91 (7)	2.777 (3)	174 (7)
OW2—H22···O4^ii	0.74 (6)	2.04 (6)	2.779 (4)	171 (6)
OW3—H31···O3^x	0.74 (7)	2.02 (7)	2.725 (3)	155 (7)
OW3—H32···O1^vi	0.71 (7)	1.99 (6)	2.693 (3)	171 (6)

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