Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103027264/fg1714sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270103027264/fg1714Isup2.hkl | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270103027264/fg1714IIsup3.hkl | |
Portable Document Format (PDF) file https://doi.org/10.1107/S0108270103027264/fg1714sup4.pdf |
CCDC references: 231037; 231038
H atoms were allowed for as riding atoms, with N1—H, N2—H and N3—H distancs of 0.86 Å and an N4—H distance of 0.89 Å.
For both compounds, data collection: CAD-4 Software (Enraf–Nonius, 1989); cell refinement: CAD-4 Software; data reduction: maXus (Mackay et al., 1999). Program(s) used to solve structure: SIR97 (Altomare et al., 1999) for (I); SIR97 (Altomare et al., 1994) for (II). For both compounds, program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976).
(CH7N4)2[ZrF6] | F(000) = 352 |
Mr = 355.43 | Dx = 2.039 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 25 reflections |
a = 6.3705 (4) Å | θ = 24.5–28.5° |
b = 6.3288 (9) Å | µ = 1.03 mm−1 |
c = 14.5630 (8) Å | T = 283 K |
β = 99.606 (4)° | Blocky, colorless |
V = 578.91 (10) Å3 | 0.50 × 0.42 × 0.20 mm |
Z = 2 |
MACH3 diffractometer | 1508 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.020 |
Graphite monochromator | θmax = 29.9°, θmin = 2.8° |
ω–2θ scans | h = −8→8 |
Absorption correction: analytical face-indexed | k = −8→8 |
Tmin = 0.619, Tmax = 0.815 | l = −1→20 |
3540 measured reflections | 5 standard reflections every 60 min |
1674 independent reflections | intensity decay: 1% |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.019 | H-atom parameters constrained |
wR(F2) = 0.049 | w = 1/[σ2(Fo2) + (0.0187P)2 + 0.0859P] where P = (Fo2 + 2Fc2)/3 |
S = 1.13 | (Δ/σ)max = 0.001 |
1674 reflections | Δρmax = 0.37 e Å−3 |
81 parameters | Δρmin = −0.58 e Å−3 |
0 restraints | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.032 (2) |
(CH7N4)2[ZrF6] | V = 578.91 (10) Å3 |
Mr = 355.43 | Z = 2 |
Monoclinic, P21/c | Mo Kα radiation |
a = 6.3705 (4) Å | µ = 1.03 mm−1 |
b = 6.3288 (9) Å | T = 283 K |
c = 14.5630 (8) Å | 0.50 × 0.42 × 0.20 mm |
β = 99.606 (4)° |
MACH3 diffractometer | 1508 reflections with I > 2σ(I) |
Absorption correction: analytical face-indexed | Rint = 0.020 |
Tmin = 0.619, Tmax = 0.815 | 5 standard reflections every 60 min |
3540 measured reflections | intensity decay: 1% |
1674 independent reflections |
R[F2 > 2σ(F2)] = 0.019 | 0 restraints |
wR(F2) = 0.049 | H-atom parameters constrained |
S = 1.13 | Δρmax = 0.37 e Å−3 |
1674 reflections | Δρmin = −0.58 e Å−3 |
81 parameters |
Experimental. Crystals were selected and optically and glass-fiber mounted in a Nonius MACH3 goniometer. Following the determination of an initial orientation matrix from reflections found using graphite-monochromated Mo radiation (λ = 0.71073 Å) in an automated search of reciprocal space, a hemisphere of data was collected in ω-2θ mode after the matrix was refined. Earlier studies showed that crystal degradation occurs on prolonged exposure to humid air, hence data were collected with an Oxford Cryostream cryostat at 283 K to provide a dry environment. Five standard reflections were measured at hourly intervals to determine the extent of possible crystal decay. The crystal orientation was monitored after every 100 intensity measurements. High-quality unit-cell dimensions were determined after data collection was complete using a selected set of 25 reflections at high 2θ within a narrow angular range. Finally, a set of reflections was selected for measurement in ψ-scan mode for later application of an empirical absorption correction. |
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. Isotropic ADPs for H1A, H1B, H2A and H2B constrained to be identical. Isotropic ADPs for H4A, H4B constrained to be identical. Although the structure had been reported earlier (Bukvetskii et al., 1990), direct methods (SIR97, Altomare et al., 1997) were used for independent solution and refinement, which proceeded without difficulty. Hydrogen atoms introduced in a riding model, with constrained geometry and identical Uiso parameters for H1a, H1b, H2a and H2b, different but identical Uiso parameters for H4a and H4b, and a third Uiso parameter for H3 refined to R = 0.0209, 0.0214 for Crystals 1 and 2 using all reflections, for a total 81 parameters varied. Lifting the constraints on H(xyz), resulting in 20 additional variables, allowed refinement to R = 0.0203, 0.0212 for Crystals 1 and 2. The R-factor ratio (Hamilton, 1965) indicates significant improvement, at the 0.005 significance level, in the fit for Crystal 1 with the additional variables, but not for Crystal 2, hence the riding model has been retained in view of the range in N—H distances, 0.76 (2)–0.88 (2) Å, for the model without H atom constraints. The final refinement statistics are given in Table 1. ? |
x | y | z | Uiso*/Ueq | ||
Zr | 0.0000 | 0.0000 | 0.0000 | 0.02129 (7) | |
F1 | 0.14989 (15) | −0.01698 (11) | 0.13163 (6) | 0.03687 (19) | |
F2 | −0.11520 (12) | 0.28481 (12) | 0.02761 (5) | 0.03881 (17) | |
F3 | 0.25215 (12) | 0.13928 (14) | −0.04050 (5) | 0.04374 (19) | |
N1 | 0.0601 (2) | 0.47438 (19) | 0.20925 (10) | 0.0393 (3) | |
H1A | 0.0106 | 0.4707 | 0.2607 | 0.046 (2)* | |
H1B | −0.0257 | 0.4801 | 0.1570 | 0.046* | |
N2 | 0.4038 (2) | 0.4626 (2) | 0.28934 (9) | 0.0378 (2) | |
H2A | 0.3572 | 0.4588 | 0.3414 | 0.046* | |
H2B | 0.5386 | 0.4607 | 0.2888 | 0.046* | |
N3 | 0.3381 (2) | 0.47995 (16) | 0.12923 (9) | 0.0331 (2) | |
H3 | 0.2490 | 0.4947 | 0.0784 | 0.046 (6)* | |
N4 | 0.55588 (19) | 0.4650 (2) | 0.12684 (10) | 0.0387 (3) | |
H4A | 0.5984 | 0.5795 | 0.0996 | 0.060 (4)* | |
H4B | 0.5808 | 0.3507 | 0.0947 | 0.060* | |
C | 0.2689 (2) | 0.47129 (17) | 0.21047 (9) | 0.0269 (2) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Zr | 0.01849 (9) | 0.02981 (10) | 0.01669 (9) | 0.00162 (4) | 0.00615 (6) | 0.00139 (4) |
F1 | 0.0334 (4) | 0.0542 (5) | 0.0219 (4) | 0.0031 (3) | 0.0011 (3) | 0.0023 (2) |
F2 | 0.0420 (4) | 0.0397 (4) | 0.0340 (3) | 0.0126 (3) | 0.0044 (3) | −0.0044 (3) |
F3 | 0.0352 (4) | 0.0617 (5) | 0.0383 (4) | −0.0147 (3) | 0.0176 (3) | −0.0007 (3) |
N1 | 0.0249 (5) | 0.0618 (7) | 0.0330 (6) | −0.0001 (4) | 0.0095 (4) | −0.0041 (4) |
N2 | 0.0291 (5) | 0.0586 (6) | 0.0261 (5) | −0.0006 (4) | 0.0059 (4) | 0.0031 (4) |
N3 | 0.0274 (5) | 0.0481 (6) | 0.0247 (5) | 0.0035 (3) | 0.0072 (4) | 0.0021 (3) |
N4 | 0.0300 (5) | 0.0498 (6) | 0.0401 (6) | 0.0026 (4) | 0.0165 (5) | 0.0046 (5) |
C | 0.0262 (5) | 0.0285 (4) | 0.0272 (6) | 0.0005 (4) | 0.0081 (4) | −0.0012 (4) |
Zr—F1i | 1.9967 (9) | N2—C | 1.3158 (17) |
Zr—F1 | 1.9967 (9) | N2—H2A | 0.86 |
Zr—F2i | 2.0119 (7) | N2—H2B | 0.86 |
Zr—F2 | 2.0119 (7) | N3—C | 1.3307 (17) |
Zr—F3i | 2.0053 (7) | N3—N4 | 1.3968 (16) |
Zr—F3 | 2.0053 (7) | N3—H3 | 0.86 |
N1—C | 1.3279 (17) | N4—H4A | 0.89 |
N1—H1A | 0.86 | N4—H4B | 0.89 |
N1—H1B | 0.86 | ||
F1—Zr—F2 | 89.33 (3) | C—N1—H1A | 120.0 |
F1—Zr—F3 | 91.59 (4) | C—N1—H1B | 120.0 |
F2—Zr—F3 | 90.10 (3) | H1A—N1—H1B | 120.0 |
F1i—Zr—F1 | 180 | C—N2—H2A | 120.0 |
F1i—Zr—F3i | 91.59 (4) | C—N2—H2B | 120.0 |
F1—Zr—F3i | 88.41 (4) | H2A—N2—H2B | 120.0 |
F1i—Zr—F3 | 88.41 (4) | C—N3—N4 | 119.81 (12) |
F3i—Zr—F3 | 180 | C—N3—H3 | 120.1 |
F1i—Zr—F2i | 89.33 (3) | N4—N3—H3 | 120.1 |
F1—Zr—F2i | 90.67 (3) | N3—N4—H4A | 109.5 |
F3i—Zr—F2i | 90.10 (3) | N3—N4—H4B | 109.5 |
F3—Zr—F2i | 89.90 (3) | H4A—N4—H4B | 109.5 |
F1i—Zr—F2 | 90.67 (3) | N1—C—N2 | 121.27 (13) |
F3i—Zr—F2 | 89.90 (3) | N1—C—N3 | 117.86 (13) |
F2i—Zr—F2 | 180 | N2—C—N3 | 120.86 (12) |
Symmetry code: (i) −x, −y, −z. |
(CH7N4)2·F6Zr | F(000) = 352 |
Mr = 355.43 | Dx = 2.039 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 25 reflections |
a = 6.3709 (3) Å | θ = 19.9–20.8° |
b = 6.3296 (3) Å | µ = 1.03 mm−1 |
c = 14.5646 (6) Å | T = 293 K |
β = 99.629 (3)° | Blocky, colorless |
V = 579.05 (5) Å3 | 0.59 × 0.37 × 0.20 mm |
Z = 2 |
MACH3 diffractometer | 1503 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.017 |
Graphite monochromator | θmax = 30.0°, θmin = 2.8° |
ω–2θ scans | h = −8→8 |
Absorption correction: ψ scan North et al., 1968 | k = −8→8 |
Tmin = 0.694, Tmax = 0.815 | l = −1→20 |
3555 measured reflections | 5 standard reflections every 60 min |
1681 independent reflections | intensity decay: 1% |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.019 | H-atom parameters constrained |
wR(F2) = 0.053 | w = 1/[σ2(Fo2) + (0.0258P)2 + 0.0641P] where P = (Fo2 + 2Fc2)/3 |
S = 1.10 | (Δ/σ)max < 0.001 |
1681 reflections | Δρmax = 0.56 e Å−3 |
81 parameters | Δρmin = −0.46 e Å−3 |
0 restraints | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0209 (17) |
(CH7N4)2·F6Zr | V = 579.05 (5) Å3 |
Mr = 355.43 | Z = 2 |
Monoclinic, P21/c | Mo Kα radiation |
a = 6.3709 (3) Å | µ = 1.03 mm−1 |
b = 6.3296 (3) Å | T = 293 K |
c = 14.5646 (6) Å | 0.59 × 0.37 × 0.20 mm |
β = 99.629 (3)° |
MACH3 diffractometer | 1503 reflections with I > 2σ(I) |
Absorption correction: ψ scan North et al., 1968 | Rint = 0.017 |
Tmin = 0.694, Tmax = 0.815 | 5 standard reflections every 60 min |
3555 measured reflections | intensity decay: 1% |
1681 independent reflections |
R[F2 > 2σ(F2)] = 0.019 | 0 restraints |
wR(F2) = 0.053 | H-atom parameters constrained |
S = 1.10 | Δρmax = 0.56 e Å−3 |
1681 reflections | Δρmin = −0.46 e Å−3 |
81 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
Zr | 0.0000 | 0.0000 | 0.0000 | 0.02124 (7) | |
F1 | 0.15005 (16) | −0.01696 (11) | 0.13172 (7) | 0.0367 (2) | |
F2 | −0.11519 (11) | 0.28480 (11) | 0.02762 (5) | 0.03881 (17) | |
F3 | 0.25212 (11) | 0.13923 (13) | −0.04047 (5) | 0.04346 (19) | |
N1 | 0.0597 (2) | 0.47446 (19) | 0.20912 (10) | 0.0395 (3) | |
H1A | 0.0102 | 0.4711 | 0.2605 | 0.043 (2)* | |
H1B | −0.0260 | 0.4799 | 0.1569 | 0.043* | |
N2 | 0.4039 (2) | 0.4630 (2) | 0.28952 (9) | 0.0373 (2) | |
H2A | 0.3571 | 0.4595 | 0.3416 | 0.043* | |
H2B | 0.5387 | 0.4610 | 0.2891 | 0.043* | |
N3 | 0.3382 (2) | 0.48007 (16) | 0.12922 (10) | 0.0327 (2) | |
H3 | 0.2492 | 0.4949 | 0.0783 | 0.048 (7)* | |
N4 | 0.5559 (2) | 0.4651 (2) | 0.12695 (10) | 0.0384 (3) | |
H4A | 0.5993 | 0.5816 | 0.1014 | 0.055 (4)* | |
H4B | 0.5804 | 0.3532 | 0.0933 | 0.055* | |
C | 0.2690 (2) | 0.47126 (17) | 0.21042 (9) | 0.0268 (2) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Zr | 0.01877 (10) | 0.02983 (10) | 0.01602 (10) | 0.00160 (3) | 0.00552 (6) | 0.00139 (3) |
F1 | 0.0332 (4) | 0.0542 (5) | 0.0212 (4) | 0.0034 (2) | 0.0002 (3) | 0.0023 (2) |
F2 | 0.0426 (4) | 0.0402 (4) | 0.0327 (3) | 0.0125 (3) | 0.0035 (3) | −0.0045 (3) |
F3 | 0.0353 (3) | 0.0614 (5) | 0.0373 (4) | −0.0141 (3) | 0.0164 (3) | −0.0005 (3) |
N1 | 0.0258 (5) | 0.0613 (7) | 0.0327 (6) | −0.0004 (4) | 0.0090 (5) | −0.0043 (4) |
N2 | 0.0286 (5) | 0.0578 (6) | 0.0259 (5) | −0.0001 (4) | 0.0057 (4) | 0.0032 (4) |
N3 | 0.0278 (5) | 0.0473 (6) | 0.0241 (5) | 0.0038 (3) | 0.0071 (4) | 0.0022 (3) |
N4 | 0.0298 (5) | 0.0498 (6) | 0.0389 (6) | 0.0024 (4) | 0.0155 (5) | 0.0050 (5) |
C | 0.0259 (5) | 0.0283 (4) | 0.0273 (6) | 0.0006 (4) | 0.0074 (4) | −0.0012 (4) |
Zr—F1i | 1.9980 (10) | N2—C | 1.3181 (18) |
Zr—F1 | 1.9980 (10) | N2—H2A | 0.8600 |
Zr—F3i | 2.0052 (6) | N2—H2B | 0.8600 |
Zr—F3 | 2.0052 (6) | N3—C | 1.3307 (18) |
Zr—F2i | 2.0121 (7) | N3—N4 | 1.3961 (16) |
Zr—F2 | 2.0121 (7) | N3—H3 | 0.8600 |
N1—C | 1.3304 (17) | N4—H4A | 0.8900 |
N1—H1A | 0.8600 | N4—H4B | 0.8900 |
N1—H1B | 0.8600 | ||
F1i—Zr—F1 | 180.00 (7) | C—N1—H1A | 120.0 |
F1i—Zr—F3i | 91.59 (4) | C—N1—H1B | 120.0 |
F1—Zr—F3i | 88.41 (4) | H1A—N1—H1B | 120.0 |
F1i—Zr—F3 | 88.41 (4) | C—N2—H2A | 120.0 |
F1—Zr—F3 | 91.59 (4) | C—N2—H2B | 120.0 |
F3i—Zr—F3 | 180.00 (6) | H2A—N2—H2B | 120.0 |
F1i—Zr—F2i | 89.32 (3) | C—N3—N4 | 119.77 (12) |
F1—Zr—F2i | 90.68 (3) | C—N3—H3 | 120.1 |
F3i—Zr—F2i | 90.11 (3) | N4—N3—H3 | 120.1 |
F3—Zr—F2i | 89.89 (3) | N3—N4—H4A | 109.5 |
F1i—Zr—F2 | 90.68 (3) | N3—N4—H4B | 109.5 |
F1—Zr—F2 | 89.32 (3) | H4A—N4—H4B | 109.5 |
F3i—Zr—F2 | 89.89 (3) | N2—C—N1 | 121.22 (13) |
F3—Zr—F2 | 90.11 (3) | N2—C—N3 | 120.93 (12) |
F2i—Zr—F2 | 180.00 (5) | N1—C—N3 | 117.85 (13) |
Symmetry code: (i) −x, −y, −z. |
Experimental details
(I) | (II) | |
Crystal data | ||
Chemical formula | (CH7N4)2[ZrF6] | (CH7N4)2·F6Zr |
Mr | 355.43 | 355.43 |
Crystal system, space group | Monoclinic, P21/c | Monoclinic, P21/c |
Temperature (K) | 283 | 293 |
a, b, c (Å) | 6.3705 (4), 6.3288 (9), 14.5630 (8) | 6.3709 (3), 6.3296 (3), 14.5646 (6) |
β (°) | 99.606 (4) | 99.629 (3) |
V (Å3) | 578.91 (10) | 579.05 (5) |
Z | 2 | 2 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 1.03 | 1.03 |
Crystal size (mm) | 0.50 × 0.42 × 0.20 | 0.59 × 0.37 × 0.20 |
Data collection | ||
Diffractometer | MACH3 diffractometer | MACH3 diffractometer |
Absorption correction | Analytical face-indexed | ψ scan North et al., 1968 |
Tmin, Tmax | 0.619, 0.815 | 0.694, 0.815 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3540, 1674, 1508 | 3555, 1681, 1503 |
Rint | 0.020 | 0.017 |
(sin θ/λ)max (Å−1) | 0.702 | 0.703 |
Refinement | ||
R[F2 > 2σ(F2)], wR(F2), S | 0.019, 0.049, 1.13 | 0.019, 0.053, 1.10 |
No. of reflections | 1674 | 1681 |
No. of parameters | 81 | 81 |
H-atom treatment | H-atom parameters constrained | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.37, −0.58 | 0.56, −0.46 |
Computer programs: CAD-4 Software (Enraf–Nonius, 1989), CAD-4 Software, maXus (Mackay et al., 1999), SIR97 (Altomare et al., 1999), SIR97 (Altomare et al., 1994), SHELXL97 (Sheldrick, 1997), ORTEPII (Johnson, 1976).
Zr—F1 | 1.9967 (9) | N2—C | 1.3158 (17) |
Zr—F2 | 2.0119 (7) | N3—C | 1.3307 (17) |
Zr—F3 | 2.0053 (7) | N3—N4 | 1.3968 (16) |
N1—C | 1.3279 (17) | ||
F1—Zr—F2 | 89.33 (3) | N1—C—N2 | 121.27 (13) |
F1—Zr—F3 | 91.59 (4) | N1—C—N3 | 117.86 (13) |
F2—Zr—F3 | 90.10 (3) | N2—C—N3 | 120.86 (12) |
C—N3—N4 | 119.81 (12) |
N-H | F | d(H···F) | angle N-H···F | d(N···F) | v.u. |
N1-H1a | F1(1) | 2.01 | 170 | 2.8630 (17) | 0.102 |
N1-H1b | F2 | 2.25 | 139 | 2.9492 (16) | 0.068 |
N2-H2a | F3(2) | 2.04 | 164 | 2.8790 (15) | 0.096 |
N2-H2b | F1(3) | 2.13 | 147 | 2.8867 (17) | 0.082 |
N3-H3 | F2(4) | 2.15 | 145 | 2.8926 (15) | 0.080 |
N4-H4a | F3(5) | 2.26 | 173 | 3.1404 (16) | 0.067 |
N4-H4b | F2(6) | 2.35 | 127 | 2.9648 (16) | 0.058 |
v.u. calculated from Brown and Altermatt (1985). Symmetry codes: (1) [-x,y + 1/2,-z + 1/2] (2) [x, −y + 1/2, z + 1/2] (3) [-x + 1, y + 1/2, −z + 1/2] (4) [-x. −y + 1, −z] (5) [-x + 1, −y + 1, −z] (6) [x + 1, y, z] |
Single crystals of aminoguanidinium(1+) pentafluorozirconate (CH7N4+·ZrF5−) have recently been shown to undergo small but highly significant radiation-induced structural changes under X-ray diffraction investigation (Ross et al., 2002). The relative stability of 2CH7N4+·ZrF62−, (I), to X-radiation was not discussed in the original structural study by Bukvetskii et al. (1990) but is of interest in view of the common cation and closely related anions in the two materials. Since crystals of (I) were grown during an investigation of the ferroelectric properties of aminoguanidinium(2+) hexafluorozirconate, CH8N42+·ZrF62− (Bauer et al., 1999), the present study was undertaken. The structures of two crystals (1 and 2) of (I) were independently determined and refined. Evidence for radiation damage was undetectable, with a variation in the standard reflections of less than 1% on average and less than 5% maximum. The results of normal probability analysis (Abrahams & Keve, 1971), based on (a) the deviates between all atomic coordinates varied in sets 1 and 2 and (b) the corresponding deviates for all Uij magnitudes, are shown in Fig. 1(a) and 1(b).
The Qexp(i)–Qnorm(i) plot of the 45 ordered atomic position coordinate deviates for sets 1 and 2, with Qexp(i) = [|(ξi(1) - ξi(2))|/(σ2(ξi(1)) + σ2(ξi(2)))1/2] where ξi(1) is the ith atomic coordinate magnitude from set 1 and ξi(2) is the ith magnitude from set 2, against the ordered normal ith deviates, Qnorm, is presented in Fig. 1(a). The magnitudes of Qnorm are conveniently calculated by the program NORMPA (Ross, 2003). Departures from linearity in the plot are minor, indicating that the residual systematic error is small. The slope of 0.69 (3) and intercept of −0.07 (3), as determined by linear regression, suggest that the joint standard uncertainty (j.s.u.) is overestimated by ~30%. The 57 Uij deviates for sets 1 and 2 in the Qexp–Qnorm plot of Fig. 1(b) contain eight outliers, viz. Zr(U13), Zr(U33), F2(U33), F3(U13), F2(U13), Zr(U11), F3(U33) and F1(U13), with respective values of 7.42, 4.98, 2.87, 2.78, 2.22, 2.08, 2.02 and 1.81. The remaining 49 Qexp values are close to linear, with a slope of 1.02 (1) and an intercept of −0.09 (12), indicative of j.s.u. values that are well estimated. Fig. 1(c) compares the positional coordinates in set 1 with those determined by Bukvetskii et al. (1990), hereafter referred to as set 3. Excluding the two outliers in Fig. 1(c), viz. F1(y) and F3(z) at 12.11 and 4.37, respectively, the departure from linearity is significantly greater than that in Fig. 1(a). The slope in Fig. 1(c) is 1.97 (6), with an intercept of −0.09 (5). The corresponding plot for coordinates from sets 2 and 3 is very similar to Fig. 1(c) and is available as part of the supplementary material (Fig. S1); the corresponding deviations are F1(y) (12.09) and F3(z) (4.22), and the slope and intercept are 2.15 (8) and −0.10 (7).
The atomic coordinates in sets 1 and 2 are hence closely comparable, each differing systematically from those in set 3, particularly F1(y), with a difference of 0.069 (6) Å [by comparison, the difference between F1(y) coordinates in these two sets is 0.0001 (10) Å]. The small systematic underestimate of standard uncertainties in the final positional parameters for sets 1 and 2 is indicative of realistic weight assignments, the close approach to linearity in Fig. 1(a) eliminating the possibility that radiation-induced structural change is observable in either. The largest outliers Qexp[Zr(U13) and Zr(U33)] are probably related to residual inaccuracies in the absorption corrections.
The [ZrF6]2− coordination octahedra are located on inversion centers (see Fig. 2a), with three unique Zr—F bonds (Table 1a), leading to an overall bond valence sum (Brown & Altermatt, 1985) of 3.91 v.u. (valence units), in good agreement with the formal ZrIV state. The octahedron is nearly ideal, with a quadratic elongation of 1.0003 and an angle variance of 1.091. Examination of the anisotropic displacement parameters (Fig. 2 b) indicates a significant elongation of the Zr(Uij) ellipsoid along the b axis (U11:U22:U33::0.62:1:0.56). Since the bonding environment of the Zr atom is nearly isotropic, this is consistent with a residual inaccuracy in the absorption correction, as noted above. The F-atom anisotropic displacement parameter values show moderate elongation (Umin/Umax = 0.28–0.48) normal to the bond axis, as expected.
The aminoguanidinium cations are in general positions; although unconstrained, their geometry is nearly ideal. The C and three N atoms of the guanidine core are slightly cupped, the deviation of the C atom from the plane containing all four atoms being 0.0042 (10) Å, whereas that of the N atoms is 0.0014 (3) Å. The deviation of the remaining N atom (N4) from this plane is 0.081 (2) Å, indicating a slight twist about the C—N3 bond; the N2—C—N3—N4 torsion angle is 4.46 (17)°. Each N—C—N bond angle (see Fig. 2c) is near the expected 120°, the largest deviation [117.9 (2)° in the N1—C—N3 angle] being similar to previous observations on the anions in CH8N4·ZrF6·H2O, CH8N4·SiF6 and (CH7N4)2·SiF6·2H2O (Ross et al., 1998, 1999). Both the N1—C—N3 and the N2—C—N3 angles in CH7N4·ZrF5 (Ross et al., 2002), however, are 119.1 (2)°.
The C(Uij) ellipsoid is relatively isotropic (Umin/Umax = 0.73), while for the N atoms, Umin/Umax is in the range 0.35–0.46, with Umax roughly normal to the plane of the cation and the bond axis, as expected.
The packing of the CH7N4+ and [ZrF6]2− ions in the unit cell is illustrated in Fig. 2(a). The anionic polyhedra occupy inversion centers and the interstitial CH7N4+ cations are oriented with the ionic plane roughly normal to the b axis (at y = 0 and 1/2). Details of the hydrogen bonds between the H and F atoms are given in Table 2. Individual calculated N—H···F bond strengths (Brown & Altermatt, 1985) are small, but these bonds are numerous enough to suggest that they may make a significant contribution to the energy of crystallization.
The robustness of this ZrF6 structure to X-radiation greatly exceeds that of CH7N4+·ZrF5− (Ross et al., 2002). Radiation-induced structural change (RISC) in the latter results in highly significant unit-cell parameter variations, together with small but highly significant structural changes. By contrast, significant differences are not detectable either among the lattice constants of all three crystals or in the atomic positions of crystals 1 and 2. The robustness may be related to the fact that the hydrogen bonds in ZrF6 (average 0.079 v.u.) are stronger than the average 0.060 v.u. hydrogen bond in CH7N4+·ZrF5−. If the reduced bond valence increases the probability that the H atoms can move from their equilibrium growth locations to adjacent potential minima in the structure on exposure to X-radiation then minor but relative realignment of the fluorozirconate ion would result. The RISC-caused atomic displacements in CH7N4+·ZrF5−, associated primarily with the Zr atom, are consistent with such a model.