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Doping the perdeuterated ammonium copper Tutton salt (ND4)2[Cu(D2O)6](SO4)2 [perdeuterated diammonium hexa­aqua­copper(II) bis­(sulfate)] with Zn leads to a change in the structure from dimorph A (low density) to dimorph B (high density). This change, which accompanies a switch in the direction of the Jahn-Teller distortion, had previously been observed to occur with substitution of Zn2+ at the Cu2+ site of between 1.3 (A) and 3.4% (B). In this study, the single-crystal neutron-diffraction analysis of (ND4)2[(Cu/Zn)(D2O)6](SO4)2 at 20 K, with 3.4% Zn doping and a deuterium substitution of 85% on the H-atom sites, reveals that the structure is entirely of type B, with the Cu/Zn site at an inversion centre and with no evidence of disorder or unusual atomic displacement parameters that might occur near a phase transition boundary.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270105009121/fa1122sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270105009121/fa1122Isup2.hkl
Contains datablock I

Comment top

The crystal structure of the ammonium copper Tutton salt is very sensitive to small perturbations, which lead to one of two possible packing motifs or dimorphs (Hathaway & Hewat, 1984; Simmons et al., 1993; Schultz et al., 1997, 2003; Hitchman et al., 1999). At room temperature and pressure, (NH4)2[Cu(H2O)6](SO4)2 adopts structure B (high density), whereas the perdeuterated salt (ND4)2[Cu(D2O)6](SO4)2 is isostructural to the alkali metal salts A2[Cu(H2O)6](SO4)2 (A = K, Rb and Cs), which adopt structure A (low density). The difference between the two structural forms is due primarily to the direction of the Jahn–Teller distortion, in which Cu—O8 is elongated in form A and Cu—O7 is elongated in form B (see Fig. 1 for atom labels). There are accompanying changes in the hydrogen-bonding network in the crystal structure, which also results in slight contractions of the a and b axes and an increase of the c axis of crystal lattice A relative to B.

The application of mild hydrostatic pressure (~200 bar at 298 K) reversibly transforms fully deuterated (ND4)2[Cu(D2O)6](SO4)2 from the A to the B form (Simmons et al., 1993; Schultz et al., 1997, 2003). From EPR (electron paramagnetic resonance) analyses, the structure was found to change abruptly from that of the pure hydrogenous salt (B) to that of the fully deuterated salt (A) at ~50% deuteration with no evidence of an intermediate phase (Henning et al., 2000). This result was confirmed with single-crystal neutron diffraction data obtained at 20 K from a crystal with 42% deuteration, which exhibited the fully hydrogenated structure B (Henning et al., 2000) without any evidence of disorder.

The hydrogenated chromium Tutton salt switches from A to B with a few percent Zn substitution on the chromium site (Araya et al., 1993), as does the deuterated copper salt (Simmons et al., 2000). From the X-ray data analyses at room temperature, it was shown that the switch from A to B occurs somewhere between 1.3 and 3.4% Zn substitution on the Cu site.

In this study, we analyzed the single-crystal neutron diffraction structure, at 20 K, of (I) with 3.4% Zn doping. From refinement of the neutron scattering length, the overall deuteration was 85.8 (4)%. As depicted in Fig. 1 and tabulated in Table 1, the structure has switched from the A form to the B form such that the Jahn–Teller distortion involves Cu1—O7 as the longest bond [2.2663 (17) Å] and Cu1—O8 as the intermediate bond [2.0041 (17) Å]. At room temperature, the structure of (I) exhibits long, intermediate and short Cu—O bond lengths [2.177 (3), 2.098 (3) and 1.965 (2) Å, respectively], apparently due to a thermal equilibrium between forms A and B. Examination of the atomic displacements parameters of (I) at 20 K provides no evidence for disorder, similar to the observation of the 42% deuterated ammonium copper [structure (V) in Table 2]. This is in contrast to the neutron structure of (NH4)2[Cr0.22Zn0.78(H2O)6](SO4)2 at 15 K, which clearly indicated the presence of disorder in the aqua ligands affected by the chromium Jahn–Teller distortion (Cotton et al., 1994).

Hydrogen-bond distances and angles are listed in Table 2. This network of hydrogen bonds is entirely consistent with those observed for other structural determinations of ammonium copper Tutton salts with structure type B (Simmons et al., 1993; Figgis et al., 2000; Henning et al., 2000; Dobe et al., 2003).

Table 3 lists Cu—O bond distances for seven low-temperature structures of ammonium copper Tutton salt with form B. Examination of Table 3 indicates that there is no systematic variation with pressure or H/D substition. However, as shown in Fig. 2, the bond distances for all of the structures appear to scale with the lattice constants.

Experimental top

A crystal of (I) was prepared by mixing a molar ratio of 2% ZnSO4·7H2O with 98% CuSO4 in a manner described previously (Simmons et al., 2000). The resulting sample was recrystallized three times from 99.8% D2O. The actual Zn/Cu ratio (3.4% Zn) was determined by analysis using a Varian SpectrAA-800 Atomic Absorption Spectrometer.

Refinement top

Three-dimensional reciprocal-space histograms were measured using the IPNS SCD instrument (Schultz et al., 1984). Indexing and integration were performed using ISAW (Chatterjee et al., 2002). Initial atomic coordinates were taken from the known structure of other Tutton salts. Refinement was first performed using GSAS (Larson & Von Dreele, 2004), and then the extinction-corrected data were input to SHELXL97 (Sheldrick, 1997) for final refinement. H atoms were refined anisotropically.

Computing details top

Data collection: IPNS SCD time-of-flight neutron Laue diffractometer (Schultz et al., 1984); cell refinement: LATCON (local program); data reduction: ANVRED (local program); program(s) used to solve structure: program (reference?); program(s) used to refine structure: GSAS (Larson & Von Dreele, 2004) and SHELXL97 (Sheldrick, 1997); molecular graphics: program (reference?); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. Neutron structure of (I) at 20 K showing displacement ellipsoids drawn at the 90% probablility level.
[Figure 2] Fig. 2. Plot of Cu—O7 and Cu—O8 distances versus the cube root of the unit cell volume for ammonium copper Tutton salts with structure B. The vertical lines correspond to structures (I)–(VII) from left to right.
perdeuterated diammonium hexaaquacopper(II) bis(sulfate) top
Crystal data top
(ND4)2[Cu(D2O)6](SO4)2F(000) = 434
Mr = 417.13The P21/a setting was used for facilitating comparisons with a large number of Tutton-salt structures that have been done in this setting. N.b. atom naming also conforms to the informal convention established in previous analyses.
Monoclinic, P21/aDx = 2.057 Mg m3
a = 9.0806 (17) ÅWhite-beam radiation, λ = 0.7-4.2 Å
b = 12.1903 (17) ÅCell parameters from 2615 reflections
c = 6.3424 (12) ŵ = 0.86 + 0.188λ cm-1 mm1
β = 106.379 (16)°T = 20 K
V = 673.6 (2) Å3Prism, blue
Z = 22.5 × 2.5 × 2.5 mm
Data collection top
IPNS single-crystal
diffractometer
1636 independent reflections
Radiation source: Intense Pulsed Neutron Source1499 reflections with I > 2σ(I)
Not applicable to TOF Laue technique monochromatorRint = 0.066
Time–of–flight Laue scansθmax = not applicable to TOF Laue technique°, θmin = 6.7°
Absorption correction: gaussian
(IPNS ANVRED; local program)
h = 1212
Tmin = 0.698, Tmax = 0.797k = 175
2162 measured reflectionsl = 29
Refinement top
Refinement on F2179 parameters
Least-squares matrix: full0 restraints
R[F2 > 2σ(F2)] = 0.054 w = 1/[σ2(Fo2) + 6.3927P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.089(Δ/σ)max = 0.008
S = 1.17Δρmax = 0.94 fm Å-3 e Å3
1636 reflectionsΔρmin = 0.93 fm Å3 e Å3
Crystal data top
(ND4)2[Cu(D2O)6](SO4)2V = 673.6 (2) Å3
Mr = 417.13Z = 2
Monoclinic, P21/aWhite-beam radiation, λ = 0.7-4.2 Å
a = 9.0806 (17) ŵ = 0.86 + 0.188λ cm-1 mm1
b = 12.1903 (17) ÅT = 20 K
c = 6.3424 (12) Å2.5 × 2.5 × 2.5 mm
β = 106.379 (16)°
Data collection top
IPNS single-crystal
diffractometer
1636 independent reflections
Absorption correction: gaussian
(IPNS ANVRED; local program)
1499 reflections with I > 2σ(I)
Tmin = 0.698, Tmax = 0.797Rint = 0.066
2162 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.054179 parameters
wR(F2) = 0.0890 restraints
S = 1.17Δρmax = 0.94 fm Å-3 e Å3
1636 reflectionsΔρmin = 0.93 fm Å3 e Å3
Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Cu10000.0053 (3)0.966 (7)
Zn10000.0053 (3)0.034 (7)
S20.4197 (4)0.1342 (3)0.7425 (5)0.0044 (6)
O30.4297 (2)0.22749 (13)0.5959 (3)0.0073 (3)
O40.55774 (18)0.06691 (14)0.7823 (3)0.0083 (3)
O50.28419 (19)0.06782 (13)0.6315 (3)0.0070 (3)
O60.4014 (2)0.17870 (13)0.9506 (3)0.0079 (3)
O70.1867 (2)0.11826 (14)0.1767 (3)0.0083 (3)
O80.15761 (19)0.10952 (13)0.0294 (3)0.0079 (3)
O90.0058 (2)0.06465 (13)0.2835 (3)0.0071 (3)
N100.14154 (12)0.34146 (8)0.35764 (18)0.0090 (2)
D110.0790 (3)0.3272 (2)0.1984 (4)0.0214 (5)0.858 (5)
H110.0790 (3)0.3272 (2)0.1984 (4)0.0214 (5)0.142 (5)
D120.2385 (3)0.29479 (19)0.3974 (4)0.0208 (5)0.858 (5)
H120.2385 (3)0.29479 (19)0.3974 (4)0.0208 (5)0.142 (5)
D130.0745 (3)0.32021 (19)0.4567 (4)0.0184 (5)0.858 (5)
H130.0745 (3)0.32021 (19)0.4567 (4)0.0184 (5)0.142 (5)
D140.1690 (3)0.42291 (18)0.3744 (4)0.0192 (5)0.858 (5)
H140.1690 (3)0.42291 (18)0.3744 (4)0.0192 (5)0.142 (5)
D150.2321 (3)0.09426 (19)0.3270 (4)0.0195 (5)0.858 (5)
H150.2321 (3)0.09426 (19)0.3270 (4)0.0195 (5)0.142 (5)
D160.2686 (3)0.12631 (19)0.1099 (4)0.0185 (5)0.858 (5)
H160.2686 (3)0.12631 (19)0.1099 (4)0.0185 (5)0.142 (5)
D170.2627 (2)0.09451 (18)0.0626 (4)0.0166 (5)0.858 (5)
H170.2627 (2)0.09451 (18)0.0626 (4)0.0166 (5)0.142 (5)
D180.1341 (3)0.18477 (17)0.0026 (4)0.0161 (5)0.858 (5)
H180.1341 (3)0.18477 (17)0.0026 (4)0.0161 (5)0.142 (5)
D190.1045 (3)0.05659 (19)0.3167 (4)0.0188 (5)0.858 (5)
H190.1045 (3)0.05659 (19)0.3167 (4)0.0188 (5)0.142 (5)
D200.0207 (3)0.14175 (17)0.3094 (4)0.0153 (5)0.858 (5)
H200.0207 (3)0.14175 (17)0.3094 (4)0.0153 (5)0.142 (5)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cu10.0056 (7)0.0056 (7)0.0047 (7)0.0005 (5)0.0012 (6)0.0017 (6)
Zn10.0056 (7)0.0056 (7)0.0047 (7)0.0005 (5)0.0012 (6)0.0017 (6)
S20.0024 (12)0.0047 (13)0.0063 (14)0.0009 (9)0.0015 (11)0.0006 (10)
O30.0081 (7)0.0062 (6)0.0072 (7)0.0010 (5)0.0015 (6)0.0007 (6)
O40.0050 (7)0.0099 (7)0.0096 (7)0.0030 (5)0.0012 (6)0.0009 (6)
O50.0059 (7)0.0068 (6)0.0076 (7)0.0013 (5)0.0008 (6)0.0007 (5)
O60.0099 (7)0.0071 (6)0.0075 (7)0.0000 (6)0.0037 (6)0.0009 (6)
O70.0074 (8)0.0100 (7)0.0072 (8)0.0005 (5)0.0014 (6)0.0005 (6)
O80.0067 (8)0.0069 (7)0.0100 (7)0.0000 (5)0.0022 (6)0.0005 (6)
O90.0078 (7)0.0072 (7)0.0063 (6)0.0002 (5)0.0020 (6)0.0015 (6)
N100.0089 (5)0.0089 (5)0.0094 (5)0.0001 (4)0.0031 (4)0.0005 (4)
D110.0240 (11)0.0262 (11)0.0120 (10)0.0068 (9)0.0015 (9)0.0032 (9)
D120.0160 (10)0.0174 (10)0.0306 (12)0.0060 (8)0.0094 (9)0.0054 (9)
D130.0187 (10)0.0220 (10)0.0168 (10)0.0006 (8)0.0090 (9)0.0024 (8)
D140.0242 (11)0.0102 (9)0.0228 (11)0.0028 (8)0.0059 (9)0.0014 (8)
D150.0204 (11)0.0237 (11)0.0129 (11)0.0006 (8)0.0020 (8)0.0019 (8)
D160.0162 (11)0.0226 (11)0.0190 (11)0.0027 (8)0.0088 (9)0.0002 (8)
D170.0117 (10)0.0177 (10)0.0192 (10)0.0005 (7)0.0026 (8)0.0005 (8)
D180.0170 (10)0.0123 (10)0.0192 (11)0.0010 (7)0.0054 (8)0.0005 (8)
D190.0156 (11)0.0208 (10)0.0222 (11)0.0023 (8)0.0087 (9)0.0024 (9)
D200.0169 (10)0.0115 (9)0.0179 (10)0.0022 (7)0.0058 (8)0.0028 (7)
Geometric parameters (Å, º) top
Cu1—O72.2663 (17)O8—D180.976 (3)
Cu1—O82.0041 (17)O8—D170.985 (3)
Cu1—O91.9774 (17)O9—D200.973 (3)
S2—O41.459 (3)O9—D190.982 (3)
S2—O51.475 (3)N10—D121.019 (3)
S2—O61.479 (4)N10—D141.022 (2)
S2—O31.488 (4)N10—D131.024 (3)
O7—D160.960 (3)N10—D111.024 (2)
O7—D150.971 (3)
O9—Cu1—O9i180.00D16—O7—D15107.3 (3)
O9—Cu1—O8i91.26 (7)D16—O7—Cu1114.31 (19)
O9—Cu1—O888.74 (7)D15—O7—Cu1110.19 (19)
O8i—Cu1—O8180.00D18—O8—D17106.5 (2)
O9—Cu1—O7i89.33 (7)D18—O8—Cu1113.77 (19)
O8—Cu1—O7i90.90 (7)D17—O8—Cu1114.75 (18)
O9—Cu1—O790.67 (7)D20—O9—D19105.0 (2)
O8—Cu1—O789.10 (7)D20—O9—Cu1118.03 (19)
O7i—Cu1—O7180.00D19—O9—Cu1114.53 (18)
O4—S2—O5109.5 (2)D12—N10—D14110.4 (2)
O4—S2—O6111.0 (2)D12—N10—D13109.2 (2)
O5—S2—O6109.8 (2)D14—N10—D13110.6 (2)
O4—S2—O3109.7 (2)D12—N10—D11110.4 (2)
O5—S2—O3108.1 (2)D14—N10—D11108.6 (2)
O6—S2—O3108.6 (2)D13—N10—D11107.6 (2)
Symmetry code: (i) x, y, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N10—D11···O6ii1.03 (1)1.91 (1)2.882 (2)157 (1)
N10—D12···O31.02 (1)2.01 (1)2.972 (2)157 (1)
N10—D13···O3iii1.02 (1)1.87 (1)2.886 (2)171 (1)
N10—D14···O5iv1.02 (1)1.82 (1)2.837 (2)173 (1)
O7—D15···O50.97 (1)1.88 (1)2.836 (3)167 (1)
O7—D16···O6v0.96 (1)1.89 (1)2.824 (3)164 (1)
O8—D17···O4vi0.99 (1)1.68 (1)2.669 (3)179 (1)
O8—D18···O6ii0.98 (1)1.74 (1)2.712 (2)177 (1)
O9—D19···O5vii0.98 (1)1.76 (1)2.730 (3)170 (1)
O9—D20···O3viii0.97 (1)1.72 (1)2.680 (2)170 (1)
Symmetry codes: (ii) x1/2, y+1/2, z1; (iii) x1/2, y+1/2, z; (iv) x+1/2, y+1/2, z+1; (v) x, y, z1; (vi) x1, y, z1; (vii) x, y, z+1; (viii) x+1/2, y1/2, z+1.

Experimental details

Crystal data
Chemical formula(ND4)2[Cu(D2O)6](SO4)2
Mr417.13
Crystal system, space groupMonoclinic, P21/a
Temperature (K)20
a, b, c (Å)9.0806 (17), 12.1903 (17), 6.3424 (12)
β (°) 106.379 (16)
V3)673.6 (2)
Z2
Radiation typeWhite-beam, λ = 0.7-4.2 Å
µ (mm1)0.86 + 0.188λ cm-1
Crystal size (mm)2.5 × 2.5 × 2.5
Data collection
DiffractometerIPNS single-crystal
diffractometer
Absorption correctionGaussian
(IPNS ANVRED; local program)
Tmin, Tmax0.698, 0.797
No. of measured, independent and
observed [I > 2σ(I)] reflections
2162, 1636, 1499
Rint0.066
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.054, 0.089, 1.17
No. of reflections1636
No. of parameters179
Δρmax, Δρmin (e Å3)0.94 fm Å-3, 0.93 fm Å3

Computer programs: IPNS SCD time-of-flight neutron Laue diffractometer (Schultz et al., 1984), LATCON (local program), ANVRED (local program), program (reference?), GSAS (Larson & Von Dreele, 2004) and SHELXL97 (Sheldrick, 1997), SHELXL97.

Selected geometric parameters (Å, º) top
Cu1—O72.2663 (17)Cu1—O91.9774 (17)
Cu1—O82.0041 (17)
O9—Cu1—O888.74 (7)O8—Cu1—O789.10 (7)
O9—Cu1—O790.67 (7)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N10—D11···O6i1.025 (3)1.910 (3)2.882 (2)157.3 (2)
N10—D12···O31.019 (3)2.010 (3)2.972 (2)156.5 (2)
N10—D13···O3ii1.024 (3)1.871 (3)2.886 (2)170.7 (2)
N10—D14···O5iii1.022 (3)1.820 (3)2.837 (2)173.0 (2)
O7—D15···O50.971 (3)1.881 (3)2.836 (3)166.8 (3)
O7—D16···O6iv0.960 (3)1.889 (3)2.824 (3)164.2 (2)
O8—D17···O4v0.985 (3)1.684 (3)2.669 (3)179.1 (2)
O8—D18···O6i0.976 (3)1.737 (3)2.712 (2)176.6 (3)
O9—D19···O5vi0.982 (3)1.758 (3)2.730 (3)169.7 (2)
O9—D20···O3vii0.973 (3)1.718 (3)2.680 (2)169.6 (3)
Symmetry codes: (i) x1/2, y+1/2, z1; (ii) x1/2, y+1/2, z; (iii) x+1/2, y+1/2, z+1; (iv) x, y, z1; (v) x1, y, z1; (vi) x, y, z+1; (vii) x+1/2, y1/2, z+1.
Comparison of Cu—O bond lengths of form B at low temperature top
StructureRadiationT (K)P (MPa)D (%)Cu—O7 (Å)Cu—O8 (Å)Cu—O9 (Å)V (Å3)ρg (Å)
Ia, 3.4% ZnN20085.8 (4)2.2663 (17)2.0041 (17)1.9774 (17)673.6 (2)0.319
IIbN1414002.272 (2)2.005 (2)1.979 (2)674.5 (2)0.324
IIIcX9.50.102.2758 (9)2.0042 (8)1.9737 (9)677.07 (12)0.333
IVd, metastableN150.1100f2.2802 (4)2.0082 (4)1.9781 (4)679.52 (8)0.333
VeN15042 (2)2.281 (1)2.007 (1)1.975 (1)677.2 (5)0.336
VIdN150.002.2834 (5)2.0077 (5)1.9792 (5)680.44 (11)0.336
VIIbN15150100f2.290 (2)2.014 (2)1.988 (3)686.4 (2)0.335
Notes: (a) this work; (b) Simmons et al., 1993); (c) Figgis et al., 2000); (d) Dobe et al., 2003); (e) Henning et al., 2000); (f) Nominal value, not refined; (g) Jahn–Teller radius ρ = [2Σ(Δdi)2]1/2, where Δdi = di − dmean.
 

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