In the title compound, [K(C12H24O6)](C6H3N2O5)·C6H4N2O5, the 18-crown-6-potassium ion is centrosymmetric, with the O atoms from o-nitro groups of the anions above and below the plane. The phenolate O atoms of adjacent anions are connected by short symmetrical hydrogen bonds [2.453 (4) Å], forming chains in the c direction.
Supporting information
CCDC reference: 209885
Key indicators
- Single-crystal X-ray study
- T = 298 K
- Mean (C-C) = 0.004 Å
- R factor = 0.040
- wR factor = 0.107
- Data-to-parameter ratio = 13.7
checkCIF results
No syntax errors found
ADDSYM reports no extra symmetry
General Notes
FORMU_01 There is a discrepancy between the atom counts in the
_chemical_formula_sum and _chemical_formula_moiety. This is
usually due to the moiety formula being in the wrong format.
Atom count from _chemical_formula_sum: C24 H31 K1 N4 O16
Atom count from _chemical_formula_moiety:C6 H4 N2 O5
Aqueous solutions of potassium 2,4-dinitrophenolate (0.1 mmol) and 18-crown-6
(0.1 mmol) were mixed and allowed to crystallize.
H atoms attached to C atoms were placed in calculated positions and allowed to
ride during the refinement. Isotropic displacement parameters were constrained
to be 1.3Ueq of the adjacent C atom. A difference synthesis showed
atom H30 at the inversion centre (0, 1/2, 1). The coordinates were fixed at
this position while the isotropic displacement parameter was allowed to
refine.
Data collection: CAD-4-PC (Enraf-Nonius, 1993); cell refinement: CAD-4-PC; data reduction: XCAD4 (Harms & Wocadlo, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.
1,4,7,10,13,16-Hexaoxacyclooctadecane-potassium hydrogen
bis(2,4-dinitrophenolate)
top
Crystal data top
C12H24KO6+·C6H3N2O5−·C6H4N2O5 | Z = 1 |
Mr = 670.63 | F(000) = 350 |
Triclinic, P1 | Dx = 1.453 Mg m−3 |
a = 7.4869 (7) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 10.3156 (18) Å | Cell parameters from 25 reflections |
c = 10.6773 (18) Å | θ = 10.0–12.0° |
α = 83.6340 (14)° | µ = 0.25 mm−1 |
β = 69.4840 (11)° | T = 298 K |
γ = 85.0830 (11)° | Lath, yellow |
V = 766.6 (2) Å3 | 0.36 × 0.18 × 0.09 mm |
Data collection top
Enraf-Nonius CAD-4 diffractometer | Rint = 0.023 |
Radiation source: fine-focus sealed tube | θmax = 25.5°, θmin = 2.0° |
Graphite monochromator | h = 0→9 |
ω–2θ scans | k = −12→12 |
3065 measured reflections | l = −12→12 |
2827 independent reflections | 3 standard reflections every 300 reflections |
1752 reflections with I > 2σ(I) | intensity decay: none |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.040 | Hydrogen site location: difference Fourier map |
wR(F2) = 0.107 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.01 | w = 1/[σ2(Fo2) + (0.0443P)2 + 0.0572P] where P = (Fo2 + 2Fc2)/3 |
2827 reflections | (Δ/σ)max = 0.003 |
206 parameters | Δρmax = 0.15 e Å−3 |
0 restraints | Δρmin = −0.15 e Å−3 |
Crystal data top
C12H24KO6+·C6H3N2O5−·C6H4N2O5 | γ = 85.0830 (11)° |
Mr = 670.63 | V = 766.6 (2) Å3 |
Triclinic, P1 | Z = 1 |
a = 7.4869 (7) Å | Mo Kα radiation |
b = 10.3156 (18) Å | µ = 0.25 mm−1 |
c = 10.6773 (18) Å | T = 298 K |
α = 83.6340 (14)° | 0.36 × 0.18 × 0.09 mm |
β = 69.4840 (11)° | |
Data collection top
Enraf-Nonius CAD-4 diffractometer | Rint = 0.023 |
3065 measured reflections | 3 standard reflections every 300 reflections |
2827 independent reflections | intensity decay: none |
1752 reflections with I > 2σ(I) | |
Refinement top
R[F2 > 2σ(F2)] = 0.040 | 0 restraints |
wR(F2) = 0.107 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.01 | Δρmax = 0.15 e Å−3 |
2827 reflections | Δρmin = −0.15 e Å−3 |
206 parameters | |
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. |
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 (Å2) top | x | y | z | Uiso*/Ueq | |
K1 | 0.0000 | 0.5000 | 0.5000 | 0.0562 (2) | |
C1 | −0.0547 (4) | 0.3112 (2) | 0.9670 (3) | 0.0597 (7) | |
C2 | −0.0467 (3) | 0.2116 (2) | 0.8836 (2) | 0.0503 (6) | |
C3 | −0.1507 (3) | 0.1015 (2) | 0.9306 (3) | 0.0517 (6) | |
H3 | −0.1406 | 0.0367 | 0.8741 | 0.067* | |
C4 | −0.2683 (3) | 0.0892 (2) | 1.0610 (3) | 0.0540 (6) | |
C5 | −0.2803 (4) | 0.1824 (3) | 1.1480 (3) | 0.0675 (7) | |
H5 | −0.3605 | 0.1723 | 1.2371 | 0.088* | |
C6 | −0.1731 (4) | 0.2892 (3) | 1.1013 (3) | 0.0690 (7) | |
H6 | −0.1787 | 0.3499 | 1.1609 | 0.090* | |
O7 | 0.0448 (3) | 0.41405 (17) | 0.9223 (2) | 0.0844 (6) | |
N8 | 0.0717 (3) | 0.2207 (2) | 0.7419 (2) | 0.0671 (6) | |
O9 | 0.1044 (3) | 0.3287 (2) | 0.6824 (2) | 0.0935 (7) | |
O10 | 0.1349 (4) | 0.1199 (2) | 0.6893 (2) | 0.1029 (8) | |
N11 | −0.3853 (3) | −0.0243 (2) | 1.1095 (3) | 0.0684 (6) | |
O12 | −0.3536 (3) | −0.11430 (18) | 1.0382 (2) | 0.0849 (6) | |
O13 | −0.5147 (3) | −0.0216 (2) | 1.2186 (2) | 0.0989 (7) | |
C21 | 0.2587 (4) | 0.3377 (3) | 0.2027 (3) | 0.0822 (9) | |
H21A | 0.3694 | 0.3011 | 0.1349 | 0.107* | |
H21B | 0.1806 | 0.3893 | 0.1579 | 0.107* | |
O22 | 0.3180 (3) | 0.41814 (18) | 0.27939 (17) | 0.0686 (5) | |
C23 | 0.4175 (4) | 0.5273 (3) | 0.2004 (3) | 0.0759 (8) | |
H23A | 0.3365 | 0.5798 | 0.1585 | 0.099* | |
H23B | 0.5310 | 0.4974 | 0.1301 | 0.099* | |
C24 | 0.4716 (4) | 0.6068 (3) | 0.2872 (3) | 0.0774 (8) | |
H24A | 0.5413 | 0.5524 | 0.3365 | 0.101* | |
H24B | 0.5530 | 0.6753 | 0.2329 | 0.101* | |
O25 | 0.3015 (2) | 0.66265 (18) | 0.37812 (17) | 0.0712 (5) | |
C26 | 0.3376 (5) | 0.7438 (3) | 0.4642 (3) | 0.0815 (9) | |
H26A | 0.4291 | 0.8075 | 0.4120 | 0.106* | |
H26B | 0.3899 | 0.6918 | 0.5258 | 0.106* | |
C27 | 0.1547 (5) | 0.8107 (3) | 0.5396 (3) | 0.0826 (9) | |
H27A | 0.1767 | 0.8743 | 0.5923 | 0.107* | |
H27B | 0.0966 | 0.8560 | 0.4778 | 0.107* | |
O28 | 0.0312 (3) | 0.71463 (16) | 0.62582 (18) | 0.0690 (5) | |
C29 | −0.1467 (5) | 0.7694 (3) | 0.7058 (3) | 0.0873 (10) | |
H29A | −0.2156 | 0.8112 | 0.6491 | 0.114* | |
H29B | −0.1269 | 0.8347 | 0.7577 | 0.114* | |
H30 | 0.0000 | 0.5000 | 1.0000 | 0.18 (2)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
K1 | 0.0628 (5) | 0.0444 (4) | 0.0528 (4) | −0.0122 (4) | −0.0073 (4) | −0.0028 (3) |
C1 | 0.0575 (15) | 0.0405 (13) | 0.093 (2) | −0.0011 (11) | −0.0394 (15) | −0.0110 (13) |
C2 | 0.0523 (14) | 0.0384 (12) | 0.0656 (15) | −0.0051 (10) | −0.0277 (12) | −0.0003 (11) |
C3 | 0.0577 (15) | 0.0362 (12) | 0.0685 (16) | −0.0031 (10) | −0.0299 (13) | −0.0066 (11) |
C4 | 0.0571 (15) | 0.0425 (13) | 0.0686 (16) | −0.0053 (11) | −0.0305 (13) | 0.0014 (12) |
C5 | 0.0657 (17) | 0.0761 (19) | 0.0667 (17) | 0.0007 (14) | −0.0292 (14) | −0.0125 (14) |
C6 | 0.0675 (18) | 0.0642 (17) | 0.088 (2) | −0.0009 (14) | −0.0358 (16) | −0.0308 (15) |
O7 | 0.0806 (13) | 0.0455 (10) | 0.1333 (18) | −0.0177 (9) | −0.0395 (13) | −0.0141 (11) |
N8 | 0.0657 (15) | 0.0659 (15) | 0.0763 (16) | −0.0173 (12) | −0.0336 (13) | 0.0078 (13) |
O9 | 0.1037 (17) | 0.0869 (15) | 0.0964 (15) | −0.0375 (13) | −0.0473 (13) | 0.0334 (12) |
O10 | 0.1202 (19) | 0.0879 (16) | 0.0808 (14) | −0.0025 (14) | −0.0072 (13) | −0.0186 (13) |
N11 | 0.0666 (15) | 0.0587 (14) | 0.0811 (16) | −0.0115 (12) | −0.0302 (14) | 0.0110 (13) |
O12 | 0.0932 (15) | 0.0481 (11) | 0.1159 (17) | −0.0195 (10) | −0.0368 (13) | −0.0019 (11) |
O13 | 0.0924 (16) | 0.0945 (16) | 0.0898 (16) | −0.0239 (13) | −0.0092 (14) | 0.0156 (13) |
C21 | 0.0703 (19) | 0.108 (2) | 0.0703 (18) | 0.0182 (18) | −0.0213 (16) | −0.0413 (18) |
O22 | 0.0660 (12) | 0.0781 (12) | 0.0558 (10) | 0.0018 (10) | −0.0134 (9) | −0.0106 (9) |
C23 | 0.0601 (17) | 0.092 (2) | 0.0557 (15) | 0.0110 (15) | −0.0023 (14) | 0.0061 (15) |
C24 | 0.0553 (17) | 0.082 (2) | 0.0797 (19) | −0.0165 (15) | −0.0084 (15) | 0.0159 (16) |
O25 | 0.0622 (12) | 0.0755 (12) | 0.0706 (12) | −0.0241 (10) | −0.0122 (10) | −0.0044 (10) |
C26 | 0.091 (2) | 0.076 (2) | 0.0826 (19) | −0.0414 (18) | −0.0337 (18) | 0.0118 (16) |
C27 | 0.124 (3) | 0.0489 (15) | 0.088 (2) | −0.0210 (17) | −0.051 (2) | −0.0020 (15) |
O28 | 0.0823 (13) | 0.0509 (10) | 0.0725 (11) | −0.0040 (9) | −0.0221 (10) | −0.0150 (9) |
C29 | 0.093 (2) | 0.074 (2) | 0.103 (2) | 0.0140 (18) | −0.036 (2) | −0.0441 (19) |
Geometric parameters (Å, º) top
K1—O9i | 2.756 (2) | N11—O13 | 1.228 (3) |
K1—O9 | 2.756 (2) | C21—O22 | 1.423 (3) |
K1—O25i | 2.7768 (16) | C21—C29i | 1.491 (4) |
K1—O25 | 2.7768 (16) | C21—H21A | 0.9700 |
K1—O28i | 2.7801 (16) | C21—H21B | 0.9700 |
K1—O28 | 2.7801 (16) | O22—C23 | 1.424 (3) |
K1—O22 | 2.8452 (17) | C23—C24 | 1.478 (4) |
K1—O22i | 2.8452 (17) | C23—H23A | 0.9700 |
C1—O7 | 1.297 (3) | C23—H23B | 0.9700 |
C1—C6 | 1.402 (4) | C24—O25 | 1.424 (3) |
C1—C2 | 1.417 (3) | C24—H24A | 0.9700 |
C2—C3 | 1.378 (3) | C24—H24B | 0.9700 |
C2—N8 | 1.458 (3) | O25—C26 | 1.415 (3) |
C3—C4 | 1.361 (3) | C26—C27 | 1.479 (4) |
C3—H3 | 0.9300 | C26—H26A | 0.9700 |
C4—C5 | 1.386 (3) | C26—H26B | 0.9700 |
C4—N11 | 1.459 (3) | C27—O28 | 1.429 (3) |
C5—C6 | 1.362 (4) | C27—H27A | 0.9700 |
C5—H5 | 0.9300 | C27—H27B | 0.9700 |
C6—H6 | 0.9300 | O28—C29 | 1.415 (3) |
O7—H30 | 1.2266 | C29—C21i | 1.491 (4) |
N8—O10 | 1.216 (3) | C29—H29A | 0.9700 |
N8—O9 | 1.219 (3) | C29—H29B | 0.9700 |
N11—O12 | 1.221 (3) | | |
| | | |
O9i—K1—O9 | 180.0 | N8—O9—K1 | 141.28 (17) |
O9i—K1—O25i | 106.43 (6) | O12—N11—O13 | 123.7 (2) |
O9—K1—O25i | 73.57 (6) | O12—N11—C4 | 118.6 (2) |
O9i—K1—O25 | 73.57 (6) | O13—N11—C4 | 117.6 (2) |
O9—K1—O25 | 106.43 (6) | O22—C21—C29i | 109.0 (2) |
O25i—K1—O25 | 180.00 (6) | O22—C21—H21A | 109.9 |
O9i—K1—O28i | 91.94 (6) | C29i—C21—H21A | 109.9 |
O9—K1—O28i | 88.06 (6) | O22—C21—H21B | 109.9 |
O25i—K1—O28i | 60.15 (5) | C29i—C21—H21B | 109.9 |
O25—K1—O28i | 119.85 (5) | H21A—C21—H21B | 108.3 |
O9i—K1—O28 | 88.06 (6) | C21—O22—C23 | 112.6 (2) |
O9—K1—O28 | 91.94 (6) | C21—O22—K1 | 110.40 (15) |
O25i—K1—O28 | 119.85 (5) | C23—O22—K1 | 110.99 (14) |
O25—K1—O28 | 60.15 (5) | O22—C23—C24 | 109.3 (2) |
O28i—K1—O28 | 180.00 (7) | O22—C23—H23A | 109.8 |
O9i—K1—O22 | 87.13 (6) | C24—C23—H23A | 109.8 |
O9—K1—O22 | 92.87 (6) | O22—C23—H23B | 109.8 |
O25i—K1—O22 | 119.88 (5) | C24—C23—H23B | 109.8 |
O25—K1—O22 | 60.12 (6) | H23A—C23—H23B | 108.3 |
O28i—K1—O22 | 61.13 (5) | O25—C24—C23 | 108.2 (2) |
O28—K1—O22 | 118.87 (5) | O25—C24—H24A | 110.1 |
O9i—K1—O22i | 92.87 (6) | C23—C24—H24A | 110.1 |
O9—K1—O22i | 87.13 (6) | O25—C24—H24B | 110.1 |
O25i—K1—O22i | 60.12 (5) | C23—C24—H24B | 110.1 |
O25—K1—O22i | 119.88 (6) | H24A—C24—H24B | 108.4 |
O28i—K1—O22i | 118.87 (5) | C26—O25—C24 | 112.9 (2) |
O28—K1—O22i | 61.13 (5) | C26—O25—K1 | 115.20 (15) |
O22—K1—O22i | 180.0 | C24—O25—K1 | 117.03 (15) |
O7—C1—C6 | 122.6 (2) | O25—C26—C27 | 108.0 (2) |
O7—C1—C2 | 122.0 (3) | O25—C26—H26A | 110.1 |
C6—C1—C2 | 115.4 (2) | C27—C26—H26A | 110.1 |
C3—C2—C1 | 122.4 (2) | O25—C26—H26B | 110.1 |
C3—C2—N8 | 116.1 (2) | C27—C26—H26B | 110.1 |
C1—C2—N8 | 121.5 (2) | H26A—C26—H26B | 108.4 |
C4—C3—C2 | 118.9 (2) | O28—C27—C26 | 108.3 (2) |
C4—C3—H3 | 120.6 | O28—C27—H27A | 110.0 |
C2—C3—H3 | 120.6 | C26—C27—H27A | 110.0 |
C3—C4—C5 | 121.4 (2) | O28—C27—H27B | 110.0 |
C3—C4—N11 | 119.0 (2) | C26—C27—H27B | 110.0 |
C5—C4—N11 | 119.5 (2) | H27A—C27—H27B | 108.4 |
C6—C5—C4 | 119.1 (3) | C29—O28—C27 | 112.8 (2) |
C6—C5—H5 | 120.4 | C29—O28—K1 | 113.70 (16) |
C4—C5—H5 | 120.4 | C27—O28—K1 | 114.52 (15) |
C5—C6—C1 | 122.7 (2) | O28—C29—C21i | 108.3 (2) |
C5—C6—H6 | 118.7 | O28—C29—H29A | 110.0 |
C1—C6—H6 | 118.7 | C21i—C29—H29A | 110.0 |
C1—O7—H30 | 113.9 | O28—C29—H29B | 110.0 |
O10—N8—O9 | 123.2 (3) | C21i—C29—H29B | 110.0 |
O10—N8—C2 | 118.3 (2) | H29A—C29—H29B | 108.4 |
O9—N8—C2 | 118.5 (2) | | |
Symmetry code: (i) −x, −y+1, −z+1. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O7—H30···O7ii | 1.23 (1) | 1.23 (1) | 2.453 (4) | 180 |
Symmetry code: (ii) −x, −y+1, −z+2. |
Experimental details
Crystal data |
Chemical formula | C12H24KO6+·C6H3N2O5−·C6H4N2O5 |
Mr | 670.63 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 298 |
a, b, c (Å) | 7.4869 (7), 10.3156 (18), 10.6773 (18) |
α, β, γ (°) | 83.6340 (14), 69.4840 (11), 85.0830 (11) |
V (Å3) | 766.6 (2) |
Z | 1 |
Radiation type | Mo Kα |
µ (mm−1) | 0.25 |
Crystal size (mm) | 0.36 × 0.18 × 0.09 |
|
Data collection |
Diffractometer | Enraf-Nonius CAD-4 diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3065, 2827, 1752 |
Rint | 0.023 |
(sin θ/λ)max (Å−1) | 0.605 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.040, 0.107, 1.01 |
No. of reflections | 2827 |
No. of parameters | 206 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.15, −0.15 |
Selected geometric parameters (Å, º) topK1—O9i | 2.756 (2) | K1—O28 | 2.7801 (16) |
K1—O9 | 2.756 (2) | K1—O22 | 2.8452 (17) |
K1—O25i | 2.7768 (16) | K1—O22i | 2.8452 (17) |
K1—O25 | 2.7768 (16) | C1—O7 | 1.297 (3) |
K1—O28i | 2.7801 (16) | O7—H30 | 1.2266 |
| | | |
O9—K1—O25 | 106.43 (6) | O9—K1—O22 | 92.87 (6) |
O9—K1—O28 | 91.94 (6) | O25—K1—O22 | 60.12 (6) |
O25—K1—O28 | 60.15 (5) | O28—K1—O22 | 118.87 (5) |
Symmetry code: (i) −x, −y+1, −z+1. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O7—H30···O7ii | 1.226 (4) | 1.226 (4) | 2.453 (4) | 180 |
Symmetry code: (ii) −x, −y+1, −z+2. |
In the title compound, (I), the asymmetric unit contains one anion with half a potassium and half a hydrogen ion, each lying on inversion centres. The potassium ion lies in the plane of the 18-crown-6 molecule, with K—O distances 2.777 (2), 2.780 (2) and 2.845 (2) Å. Eightfold coordination of the potassium is completed by O9 and O9'(-x, 1 - y, 1 - z) from o-nitro groups on either side of the crown [2.756 (2) Å] (Fig. 1). Phenolate atom O7 is 2.453 (4) Å from O7'(-x, 1 - y, 2 - z), with the hydrogen ion, H30, at the mid-point (0, 1/2, 1) to give a typical short symmetrical hydrogen bond. These hydrogen bonds connect the molecules into zigzag chains in the c direction.
The Cambridge Structural Database (Allen, 2002) lists over 300 structures containing the 18-crown-6-potassium cation. When two ligands are available, as in (I), the cation can be centrosymmetric, for example, Bryn & Strouse (1981). More often, the potassium ion is out of the ring plane and is coordinated by one or two ligand atoms on the side away from the crown. The potassium ion can lie as much as 1.6 Å out of the plane of the crown O atoms (Ziolo et al., 1981), but is usually closer to the plane. For example, in 18-crown-6-potassium propiophenone (Veya et al., 1994), the potassium ion is 0.678 Å out of the plane.
In 18-crown-6 [2,6-bis(trifluoromethyl)phenylphosphanyl]potassium (Rudzevich et al., 2002), the potassium ion is 0.465 Å out of the plane. In these examples, the exposed face of the potassium is coordinated by one atom from the anion. In 18-crown-6 potassium picrate (Barnes & Collard, 1988), the potassium ion is 0.678 Å out of the plane and is coordinated by the phenol O atom and an O atom from an o-nitro group of the same anion at distances of 2.741 (3) and 2.846 (4) Å, respectively.
Coordination of nitrophenolate anions to potassium ions by O atoms from o-nitro groups occurs in potassium picrate (Palenik, 1972) and in potassium 2,4-dinitrophenolate (Chaloner et al., 1998), as well as in 18-crown-6 potassium picrate (Barnes & Collard, 1988). The phenolate O atom is usually involved as well. In (I), the phenolate O atom is not involved because of the opportunity to form a strong hydrogen bond and restricted access to the potassium ion lying in the ring plane. The plane of the phenyl ring makes an angle of 22.9 (1)° with the plane of the crown. The p-nitro group is twisted by 12.9 (4)° from the plane of the phenyl group compared with 30.2 (3)° for the o-nitro group. These values are typical of p- and o-nitro groups of nitrobenzenes (Barnes & Chudek, 2003). Coordination to three O atoms from nitro groups of two bridging anions in a dimeric complex has also been observed (Barne et al., 1994).