Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807028541/lh2412sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536807028541/lh2412Isup2.hkl |
CCDC reference: 654968
Key indicators
- Single-crystal X-ray study
- T = 90 K
- Mean (C-C) = 0.002 Å
- R factor = 0.041
- wR factor = 0.114
- Data-to-parameter ratio = 14.5
checkCIF/PLATON results
No syntax errors found
Alert level B PLAT430_ALERT_2_B Short Inter D...A Contact O1 .. O1 .. 2.75 Ang.
Alert level C PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical . ? PLAT230_ALERT_2_C Hirshfeld Test Diff for O1 - N1 .. 5.26 su
0 ALERT level A = In general: serious problem 1 ALERT level B = Potentially serious problem 2 ALERT level C = Check and explain 0 ALERT level G = General alerts; check 1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 2 ALERT type 2 Indicator that the structure model may be wrong or deficient 0 ALERT type 3 Indicator that the structure quality may be low 0 ALERT type 4 Improvement, methodology, query or suggestion 0 ALERT type 5 Informative message, check
The title compound was prepared by nitration of benzyl 2,6-dihydroxybenzoate and recrystallization of the resultant product from ethyl acetate afforded pale yellow coloured crystals. 1H NMR (DMSO-d6, p.p.m.): δ 5.31 (s, 2H), 6.57 (d, 1H), 7.32–7.44 (m, 5H), 8.03 (d, 1H), 10.95(s, 1H), 11.70 (s, 1H).
H atoms were found in difference Fourier maps and subsequently placed in idealized positions with constrained C—H distances of 0.95 Å (Car—H), 0.99 Å (CH2) and 0.84 Å (O—H). Uiso(H) values were set to 1.5Ueq(OH only) or 1.2eq of the attached atom.
Phenolic acids are widely distributed in plants and they have been the subject of a great number of chemical, biological, agricultural, and medicinal studies (Herrmann, 1989). Hydroxybenzoic acids occur in food plants as esters or glycosides conjugated with other natural compounds such as flavonoids, alcohols, hydroxfatty acids, sterols, and glucosides. The alkyl esters of p-hydroxybenzoic acids are used extensively in the preservation of pharmaceuticals, because they are relatively nonirritating and nontoxic and offer good antimicrobial coverage. 2,6-Dihydroxybenzoic acid derivatives are known to exhibit anthelmintic activity, especially the 3-nitro analogue (Rushcig et al., 1973). In view of the biological activity associated with hydroxybenzoic acids, we have undertaken the synthesis of benzyl 2,6-dihydroxy-3-nitrobenzoate. In order to confirm the position of attachment of nitro group on the phenyl ring and to obtain more detailed information on the structural conformation of the molecule, its X-ray structure determination has been carried out.
X-ray crystallography confirmed the molecular structure and atom connectivity as illustrated in Fig. 1. In the title molecule the nitro group shows normal geometrical parameters. The torsion angles [O1—N1—C1—C6 = -176.75 (11) and O2—N1—C1—C2 = -177.50 (11) Å] indicate that there is not much deviation of nitro group plane from the plane of phenyl ring, facilitating conjugation with π electrons of the phenyl ring. Furthermore,the observed length of the N1—C1 bond [1.4329 (16) Å] is shorter than the theoretical length for a Car—NO2 bond of [1.468 (14) Å; Allen et al., 1987], which indicates the formation of a conjugated π-electron system along this bond. There is an asymmetry of the exocyclic angles at C1, C2, C3, C4, and C9 atoms.
The mode of packing of the title compound along the b direction is illustrated in Fig. 2. In addition to O—H···O intra and intermolecular hydrogen bonding and C—H···O interactions contribute to the stabilization of the crystal structure.
For related literature, see: Herrmann (1989); Rushcig et al. (1973); Wilson (1992).
Data collection: COLLECT (Nonius, 1999); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL (Sheldrick, 1995); software used to prepare material for publication: SHELXL97 and local procedures.
C14H11NO6 | F(000) = 600 |
Mr = 289.24 | Dx = 1.563 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 3037 reflections |
a = 10.0050 (3) Å | θ = 1.0–27.5° |
b = 6.1633 (2) Å | µ = 0.12 mm−1 |
c = 20.1048 (6) Å | T = 90 K |
β = 97.5817 (12)° | Cut plate, pale yellow |
V = 1228.90 (7) Å3 | 0.30 × 0.25 × 0.08 mm |
Z = 4 |
Bruker Nonius KappaCCD area-detector diffractometer | 2791 independent reflections |
Radiation source: fine-focus sealed tube | 2280 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.017 |
Detector resolution: 18 pixels mm-1 | θmax = 27.5°, θmin = 2.1° |
ω scans at fixed χ = 55° | h = −12→12 |
Absorption correction: multi-scan (SCALEPACK; Otwinowski & Minor, 1997) | k = −7→7 |
Tmin = 0.964, Tmax = 0.990 | l = −26→25 |
5320 measured reflections |
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)] = 0.041 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.114 | H-atom parameters constrained |
S = 1.03 | w = 1/[σ2(Fo2) + (0.0656P)2 + 0.3636P] where P = (Fo2 + 2Fc2)/3 |
2791 reflections | (Δ/σ)max < 0.001 |
192 parameters | Δρmax = 0.29 e Å−3 |
0 restraints | Δρmin = −0.27 e Å−3 |
C14H11NO6 | V = 1228.90 (7) Å3 |
Mr = 289.24 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 10.0050 (3) Å | µ = 0.12 mm−1 |
b = 6.1633 (2) Å | T = 90 K |
c = 20.1048 (6) Å | 0.30 × 0.25 × 0.08 mm |
β = 97.5817 (12)° |
Bruker Nonius KappaCCD area-detector diffractometer | 2791 independent reflections |
Absorption correction: multi-scan (SCALEPACK; Otwinowski & Minor, 1997) | 2280 reflections with I > 2σ(I) |
Tmin = 0.964, Tmax = 0.990 | Rint = 0.017 |
5320 measured reflections |
R[F2 > 2σ(F2)] = 0.041 | 0 restraints |
wR(F2) = 0.114 | H-atom parameters constrained |
S = 1.03 | Δρmax = 0.29 e Å−3 |
2791 reflections | Δρmin = −0.27 e Å−3 |
192 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 | ||
N1 | −0.10725 (11) | −0.29419 (18) | 0.39249 (5) | 0.0213 (2) | |
O1 | −0.06977 (9) | −0.40479 (15) | 0.44407 (4) | 0.0240 (2) | |
O2 | −0.20301 (10) | −0.35119 (16) | 0.35140 (5) | 0.0287 (2) | |
O3 | 0.12549 (9) | −0.14652 (14) | 0.47955 (4) | 0.0217 (2) | |
H3 | 0.0773 | −0.2569 | 0.4824 | 0.033* | |
O4 | 0.13652 (10) | 0.48223 (15) | 0.34164 (5) | 0.0245 (2) | |
H4 | 0.2018 | 0.5127 | 0.3708 | 0.037* | |
O5 | 0.30779 (9) | 0.43345 (15) | 0.44313 (5) | 0.0252 (2) | |
O6 | 0.31031 (9) | 0.13490 (15) | 0.50629 (4) | 0.0209 (2) | |
C1 | −0.03792 (12) | −0.0967 (2) | 0.38146 (6) | 0.0194 (3) | |
C2 | 0.07555 (12) | −0.0302 (2) | 0.42602 (6) | 0.0180 (3) | |
C3 | 0.13804 (12) | 0.1685 (2) | 0.41310 (6) | 0.0186 (3) | |
C4 | 0.08403 (13) | 0.2913 (2) | 0.35642 (6) | 0.0202 (3) | |
C5 | −0.02761 (13) | 0.2183 (2) | 0.31257 (6) | 0.0227 (3) | |
H5 | −0.0613 | 0.3018 | 0.2743 | 0.027* | |
C6 | −0.08734 (13) | 0.0270 (2) | 0.32527 (6) | 0.0218 (3) | |
H6 | −0.1631 | −0.0229 | 0.2958 | 0.026* | |
C7 | 0.25843 (13) | 0.2571 (2) | 0.45507 (6) | 0.0197 (3) | |
C8 | 0.43003 (13) | 0.2209 (2) | 0.54614 (6) | 0.0220 (3) | |
H8A | 0.4099 | 0.3632 | 0.5654 | 0.026* | |
H8B | 0.5027 | 0.2413 | 0.5177 | 0.026* | |
C9 | 0.47396 (12) | 0.0615 (2) | 0.60144 (6) | 0.0198 (3) | |
C10 | 0.40299 (13) | −0.1265 (2) | 0.61159 (6) | 0.0232 (3) | |
H10 | 0.3224 | −0.1593 | 0.5828 | 0.028* | |
C11 | 0.44938 (14) | −0.2668 (2) | 0.66366 (6) | 0.0256 (3) | |
H11 | 0.4000 | −0.3949 | 0.6703 | 0.031* | |
C12 | 0.56721 (14) | −0.2217 (2) | 0.70606 (6) | 0.0245 (3) | |
H12 | 0.5984 | −0.3179 | 0.7416 | 0.029* | |
C13 | 0.63878 (13) | −0.0346 (2) | 0.69588 (7) | 0.0251 (3) | |
H13 | 0.7198 | −0.0026 | 0.7244 | 0.030* | |
C14 | 0.59223 (13) | 0.1064 (2) | 0.64395 (6) | 0.0246 (3) | |
H14 | 0.6416 | 0.2345 | 0.6374 | 0.029* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0200 (5) | 0.0208 (6) | 0.0230 (5) | −0.0004 (4) | 0.0030 (4) | −0.0026 (4) |
O1 | 0.0264 (5) | 0.0213 (5) | 0.0240 (5) | −0.0030 (4) | 0.0022 (4) | 0.0032 (4) |
O2 | 0.0254 (5) | 0.0280 (5) | 0.0306 (5) | −0.0072 (4) | −0.0043 (4) | −0.0016 (4) |
O3 | 0.0225 (5) | 0.0179 (5) | 0.0237 (4) | −0.0032 (4) | −0.0009 (4) | 0.0039 (4) |
O4 | 0.0250 (5) | 0.0206 (5) | 0.0271 (5) | −0.0031 (4) | 0.0005 (4) | 0.0054 (4) |
O5 | 0.0258 (5) | 0.0209 (5) | 0.0282 (5) | −0.0054 (4) | 0.0004 (4) | 0.0037 (4) |
O6 | 0.0200 (5) | 0.0199 (5) | 0.0217 (4) | −0.0028 (3) | −0.0021 (3) | 0.0014 (4) |
C1 | 0.0193 (6) | 0.0175 (6) | 0.0217 (6) | 0.0001 (5) | 0.0043 (5) | −0.0019 (5) |
C2 | 0.0184 (6) | 0.0180 (6) | 0.0178 (6) | 0.0027 (5) | 0.0031 (4) | −0.0011 (5) |
C3 | 0.0178 (6) | 0.0186 (6) | 0.0197 (6) | 0.0001 (5) | 0.0030 (5) | −0.0006 (5) |
C4 | 0.0205 (6) | 0.0184 (6) | 0.0223 (6) | 0.0017 (5) | 0.0053 (5) | 0.0006 (5) |
C5 | 0.0229 (6) | 0.0237 (7) | 0.0210 (6) | 0.0022 (5) | 0.0010 (5) | 0.0025 (5) |
C6 | 0.0195 (6) | 0.0245 (7) | 0.0208 (6) | 0.0013 (5) | 0.0009 (5) | −0.0024 (5) |
C7 | 0.0205 (6) | 0.0189 (6) | 0.0201 (6) | 0.0014 (5) | 0.0040 (5) | −0.0003 (5) |
C8 | 0.0202 (6) | 0.0221 (6) | 0.0229 (6) | −0.0044 (5) | −0.0005 (5) | −0.0007 (5) |
C9 | 0.0188 (6) | 0.0220 (7) | 0.0189 (6) | −0.0005 (5) | 0.0031 (5) | −0.0023 (5) |
C10 | 0.0212 (6) | 0.0243 (7) | 0.0233 (6) | −0.0039 (5) | −0.0002 (5) | −0.0015 (5) |
C11 | 0.0274 (7) | 0.0232 (7) | 0.0257 (7) | −0.0043 (5) | 0.0017 (5) | 0.0007 (5) |
C12 | 0.0246 (7) | 0.0268 (7) | 0.0218 (6) | 0.0028 (5) | 0.0015 (5) | 0.0019 (5) |
C13 | 0.0182 (6) | 0.0334 (8) | 0.0232 (6) | −0.0016 (5) | 0.0001 (5) | −0.0013 (5) |
C14 | 0.0212 (6) | 0.0279 (7) | 0.0243 (6) | −0.0060 (5) | 0.0018 (5) | 0.0003 (5) |
N1—O2 | 1.2308 (14) | C5—H5 | 0.9500 |
N1—O1 | 1.2563 (14) | C6—H6 | 0.9500 |
N1—C1 | 1.4329 (16) | C8—C9 | 1.5051 (18) |
O3—C2 | 1.3339 (15) | C8—H8A | 0.9900 |
O3—H3 | 0.8400 | C8—H8B | 0.9900 |
O4—C4 | 1.3381 (15) | C9—C10 | 1.3879 (18) |
O4—H4 | 0.8400 | C9—C14 | 1.3929 (17) |
O5—C7 | 1.2303 (16) | C10—C11 | 1.3897 (19) |
O6—C7 | 1.3253 (15) | C10—H10 | 0.9500 |
O6—C8 | 1.4507 (15) | C11—C12 | 1.3887 (18) |
C1—C6 | 1.3977 (18) | C11—H11 | 0.9500 |
C1—C2 | 1.4109 (17) | C12—C13 | 1.387 (2) |
C2—C3 | 1.4147 (18) | C12—H12 | 0.9500 |
C3—C4 | 1.4144 (17) | C13—C14 | 1.3904 (19) |
C3—C7 | 1.4809 (17) | C13—H13 | 0.9500 |
C4—C5 | 1.4026 (18) | C14—H14 | 0.9500 |
C5—C6 | 1.3614 (19) | ||
O2—N1—O1 | 121.36 (11) | O6—C7—C3 | 116.02 (11) |
O2—N1—C1 | 119.24 (11) | O6—C8—C9 | 107.98 (10) |
O1—N1—C1 | 119.40 (10) | O6—C8—H8A | 110.1 |
C2—O3—H3 | 109.5 | C9—C8—H8A | 110.1 |
C4—O4—H4 | 109.5 | O6—C8—H8B | 110.1 |
C7—O6—C8 | 115.57 (10) | C9—C8—H8B | 110.1 |
C6—C1—C2 | 121.62 (12) | H8A—C8—H8B | 108.4 |
C6—C1—N1 | 117.47 (11) | C10—C9—C14 | 119.01 (12) |
C2—C1—N1 | 120.91 (11) | C10—C9—C8 | 123.25 (11) |
O3—C2—C1 | 122.74 (11) | C14—C9—C8 | 117.73 (11) |
O3—C2—C3 | 119.06 (11) | C9—C10—C11 | 120.26 (12) |
C1—C2—C3 | 118.20 (11) | C9—C10—H10 | 119.9 |
C4—C3—C2 | 118.69 (11) | C11—C10—H10 | 119.9 |
C4—C3—C7 | 117.21 (11) | C12—C11—C10 | 120.66 (13) |
C2—C3—C7 | 124.10 (11) | C12—C11—H11 | 119.7 |
O4—C4—C5 | 116.47 (11) | C10—C11—H11 | 119.7 |
O4—C4—C3 | 122.01 (11) | C13—C12—C11 | 119.27 (12) |
C5—C4—C3 | 121.52 (12) | C13—C12—H12 | 120.4 |
C6—C5—C4 | 119.52 (12) | C11—C12—H12 | 120.4 |
C6—C5—H5 | 120.2 | C12—C13—C14 | 120.13 (12) |
C4—C5—H5 | 120.2 | C12—C13—H13 | 119.9 |
C5—C6—C1 | 120.44 (12) | C14—C13—H13 | 119.9 |
C5—C6—H6 | 119.8 | C13—C14—C9 | 120.67 (13) |
C1—C6—H6 | 119.8 | C13—C14—H14 | 119.7 |
O5—C7—O6 | 121.84 (11) | C9—C14—H14 | 119.7 |
O5—C7—C3 | 122.14 (11) | ||
O2—N1—C1—C6 | 2.73 (17) | C2—C1—C6—C5 | −0.95 (19) |
O1—N1—C1—C6 | −176.75 (11) | N1—C1—C6—C5 | 178.81 (11) |
O2—N1—C1—C2 | −177.50 (11) | C8—O6—C7—O5 | −1.20 (17) |
O1—N1—C1—C2 | 3.01 (18) | C8—O6—C7—C3 | 178.63 (10) |
C6—C1—C2—O3 | −179.24 (11) | C4—C3—C7—O5 | 2.46 (18) |
N1—C1—C2—O3 | 1.01 (19) | C2—C3—C7—O5 | −178.09 (12) |
C6—C1—C2—C3 | 0.95 (18) | C4—C3—C7—O6 | −177.38 (10) |
N1—C1—C2—C3 | −178.81 (11) | C2—C3—C7—O6 | 2.08 (18) |
O3—C2—C3—C4 | −179.70 (11) | C7—O6—C8—C9 | 179.99 (10) |
C1—C2—C3—C4 | 0.12 (17) | O6—C8—C9—C10 | −3.07 (17) |
O3—C2—C3—C7 | 0.85 (18) | O6—C8—C9—C14 | 176.59 (11) |
C1—C2—C3—C7 | −179.33 (11) | C14—C9—C10—C11 | 0.3 (2) |
C2—C3—C4—O4 | 178.95 (11) | C8—C9—C10—C11 | 179.95 (12) |
C7—C3—C4—O4 | −1.57 (18) | C9—C10—C11—C12 | −0.2 (2) |
C2—C3—C4—C5 | −1.20 (19) | C10—C11—C12—C13 | −0.1 (2) |
C7—C3—C4—C5 | 178.28 (11) | C11—C12—C13—C14 | 0.4 (2) |
O4—C4—C5—C6 | −178.91 (11) | C12—C13—C14—C9 | −0.3 (2) |
C3—C4—C5—C6 | 1.2 (2) | C10—C9—C14—C13 | −0.1 (2) |
C4—C5—C6—C1 | −0.14 (19) | C8—C9—C14—C13 | −179.75 (12) |
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3···O1 | 0.84 | 1.81 | 2.5478 (12) | 145 |
O3—H3···N1 | 0.84 | 2.42 | 2.8703 (14) | 114 |
O3—H3···O1i | 0.84 | 2.56 | 3.2469 (13) | 139 |
O4—H4···O5 | 0.84 | 1.75 | 2.5034 (13) | 148 |
Symmetry code: (i) −x, −y−1, −z+1. |
Experimental details
Crystal data | |
Chemical formula | C14H11NO6 |
Mr | 289.24 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 90 |
a, b, c (Å) | 10.0050 (3), 6.1633 (2), 20.1048 (6) |
β (°) | 97.5817 (12) |
V (Å3) | 1228.90 (7) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.12 |
Crystal size (mm) | 0.30 × 0.25 × 0.08 |
Data collection | |
Diffractometer | Bruker Nonius KappaCCD area-detector |
Absorption correction | Multi-scan (SCALEPACK; Otwinowski & Minor, 1997) |
Tmin, Tmax | 0.964, 0.990 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 5320, 2791, 2280 |
Rint | 0.017 |
(sin θ/λ)max (Å−1) | 0.649 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.041, 0.114, 1.03 |
No. of reflections | 2791 |
No. of parameters | 192 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.29, −0.27 |
Computer programs: COLLECT (Nonius, 1999), SCALEPACK (Otwinowski & Minor, 1997), DENZO-SMN (Otwinowski & Minor, 1997), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), XP in SHELXTL (Sheldrick, 1995), SHELXL97 and local procedures.
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3···O1 | 0.84 | 1.81 | 2.5478 (12) | 144.9 |
O3—H3···N1 | 0.84 | 2.42 | 2.8703 (14) | 114.4 |
O3—H3···O1i | 0.84 | 2.56 | 3.2469 (13) | 139.4 |
O4—H4···O5 | 0.84 | 1.75 | 2.5034 (13) | 147.9 |
Symmetry code: (i) −x, −y−1, −z+1. |
Phenolic acids are widely distributed in plants and they have been the subject of a great number of chemical, biological, agricultural, and medicinal studies (Herrmann, 1989). Hydroxybenzoic acids occur in food plants as esters or glycosides conjugated with other natural compounds such as flavonoids, alcohols, hydroxfatty acids, sterols, and glucosides. The alkyl esters of p-hydroxybenzoic acids are used extensively in the preservation of pharmaceuticals, because they are relatively nonirritating and nontoxic and offer good antimicrobial coverage. 2,6-Dihydroxybenzoic acid derivatives are known to exhibit anthelmintic activity, especially the 3-nitro analogue (Rushcig et al., 1973). In view of the biological activity associated with hydroxybenzoic acids, we have undertaken the synthesis of benzyl 2,6-dihydroxy-3-nitrobenzoate. In order to confirm the position of attachment of nitro group on the phenyl ring and to obtain more detailed information on the structural conformation of the molecule, its X-ray structure determination has been carried out.
X-ray crystallography confirmed the molecular structure and atom connectivity as illustrated in Fig. 1. In the title molecule the nitro group shows normal geometrical parameters. The torsion angles [O1—N1—C1—C6 = -176.75 (11) and O2—N1—C1—C2 = -177.50 (11) Å] indicate that there is not much deviation of nitro group plane from the plane of phenyl ring, facilitating conjugation with π electrons of the phenyl ring. Furthermore,the observed length of the N1—C1 bond [1.4329 (16) Å] is shorter than the theoretical length for a Car—NO2 bond of [1.468 (14) Å; Allen et al., 1987], which indicates the formation of a conjugated π-electron system along this bond. There is an asymmetry of the exocyclic angles at C1, C2, C3, C4, and C9 atoms.
The mode of packing of the title compound along the b direction is illustrated in Fig. 2. In addition to O—H···O intra and intermolecular hydrogen bonding and C—H···O interactions contribute to the stabilization of the crystal structure.