| Literature DB >> 21581317 |
Hoong-Kun Fun, Hadi Kargar, Reza Kia.
Abstract
The asymmetric unit of the potential mono-Schiff base ligand title compound, C(13)H(10)N(4), contains two crystallographically independent mol-ecules, A and B. In mol-ecule A, the two rings are twisted from each other by 13.90 (18)°. By contrast, the dihedral angle between the two rings in mol-ecule B is 0.67 (19)°. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯N inter-actions via R(4) (4)(32) motifs, forming two-dimensional arrays. The short distances between the centroids of the six-membered rings indicate the existence of π-π inter-actions [centroid-centroid distances = 3.6880 (17)-3.7466 (15) Å].Entities:
Year: 2008 PMID: 21581317 PMCID: PMC2959807 DOI: 10.1107/S1600536808037070
Source DB: PubMed Journal: Acta Crystallogr Sect E Struct Rep Online ISSN: 1600-5368
| C13H10N4 | |
| Monoclinic, | Mo |
| Hall symbol: -P 2ybc | Cell parameters from 1699 reflections |
| θ = 2.3–30.1º | |
| µ = 0.09 mm−1 | |
| β = 124.651 (2)º | Needle, yellow |
| 0.45 × 0.09 × 0.07 mm | |
| Bruker SMART APEXII CCD area-detector diffractometer | 3810 independent reflections |
| Radiation source: fine-focus sealed tube | 2372 reflections with |
| Monochromator: graphite | |
| θmax = 25.0º | |
| φ and ω scans | θmin = 1.8º |
| Absorption correction: multi-scan( | |
| 18251 measured reflections |
| Refinement on | Secondary atom site location: difference Fourier map |
| Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
| H atoms treated by a mixture of independent and constrained refinement | |
| | |
| (Δ/σ)max < 0.001 | |
| 3810 reflections | Δρmax = 0.63 e Å−3 |
| 323 parameters | Δρmin = −0.29 e Å−3 |
| Primary atom site location: structure-invariant direct methods | Extinction correction: none |
| Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment. |
| 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 |
| N1A | 0.6639 (2) | 0.12555 (19) | 0.38263 (17) | 0.0217 (6) | |
| N2A | 0.85668 (19) | 0.33048 (19) | 0.36498 (16) | 0.0148 (6) | |
| N3A | 0.9556 (2) | 0.1387 (2) | 0.3572 (2) | 0.0277 (7) | |
| N4A | 1.0578 (2) | 0.9061 (2) | 0.36363 (17) | 0.0227 (6) | |
| C1A | 0.8618 (2) | 0.1349 (2) | 0.36579 (19) | 0.0185 (7) | |
| C2A | 0.8126 (2) | 0.0361 (2) | 0.36880 (19) | 0.0200 (7) | |
| H2AA | 0.8447 | −0.0292 | 0.3654 | 0.024* | |
| C3A | 0.7163 (2) | 0.0359 (2) | 0.3769 (2) | 0.0210 (7) | |
| H3AA | 0.6856 | −0.0312 | 0.3784 | 0.025* | |
| C4A | 0.7119 (2) | 0.2198 (2) | 0.37969 (19) | 0.0184 (7) | |
| H4AA | 0.6773 | 0.2833 | 0.3834 | 0.022* | |
| C5A | 0.8084 (2) | 0.2316 (2) | 0.37159 (19) | 0.0156 (6) | |
| C6A | 0.8305 (2) | 0.4207 (2) | 0.38827 (19) | 0.0173 (7) | |
| H6AA | 0.7799 | 0.4207 | 0.4104 | 0.021* | |
| C7A | 0.8790 (2) | 0.5238 (2) | 0.38050 (18) | 0.0140 (6) | |
| C8A | 0.9575 (2) | 0.5272 (2) | 0.34913 (18) | 0.0189 (7) | |
| H8AA | 0.9781 | 0.4632 | 0.3313 | 0.023* | |
| C9A | 1.0037 (2) | 0.6245 (2) | 0.34472 (19) | 0.0203 (7) | |
| H9AA | 1.0551 | 0.6263 | 0.3234 | 0.024* | |
| C10A | 0.9739 (2) | 0.7212 (2) | 0.37224 (19) | 0.0156 (6) | |
| C11A | 0.8961 (2) | 0.7180 (2) | 0.40366 (19) | 0.0185 (7) | |
| H11A | 0.8755 | 0.7819 | 0.4217 | 0.022* | |
| C12A | 0.8499 (2) | 0.6198 (2) | 0.40791 (19) | 0.0168 (7) | |
| H12A | 0.7987 | 0.6179 | 0.4294 | 0.020* | |
| C13A | 1.0218 (2) | 0.8236 (2) | 0.36773 (19) | 0.0173 (6) | |
| C3B | 0.7831 (2) | −0.3515 (2) | 0.62159 (19) | 0.0202 (7) | |
| H3BA | 0.8150 | −0.4183 | 0.6211 | 0.024* | |
| N2B | 0.63747 (19) | −0.05867 (19) | 0.62738 (16) | 0.0183 (6) | |
| N3B | 0.5661 (2) | −0.2465 (2) | 0.66987 (19) | 0.0236 (6) | |
| N4B | 0.4350 (2) | 0.5212 (2) | 0.62229 (18) | 0.0269 (6) | |
| C1B | 0.6482 (2) | −0.2527 (2) | 0.64597 (19) | 0.0160 (7) | |
| C2B | 0.6988 (2) | −0.3504 (2) | 0.6444 (2) | 0.0191 (7) | |
| H2BA | 0.6757 | −0.4152 | 0.6588 | 0.023* | |
| N1B | 0.8223 (2) | −0.26157 (19) | 0.59977 (17) | 0.0225 (6) | |
| C4B | 0.7739 (3) | −0.1680 (2) | 0.6022 (2) | 0.0232 (7) | |
| H4BA | 0.7994 | −0.1047 | 0.5878 | 0.028* | |
| C5B | 0.6885 (2) | −0.1573 (2) | 0.62439 (19) | 0.0153 (6) | |
| C6B | 0.6661 (2) | 0.0318 (2) | 0.6087 (2) | 0.0207 (7) | |
| H6BA | 0.7215 | 0.0325 | 0.5916 | 0.025* | |
| C7B | 0.6158 (2) | 0.1352 (2) | 0.61273 (19) | 0.0156 (6) | |
| C8B | 0.5309 (2) | 0.1391 (2) | 0.63648 (19) | 0.0177 (7) | |
| H8BA | 0.5058 | 0.0751 | 0.6501 | 0.021* | |
| C9B | 0.4837 (3) | 0.2381 (2) | 0.6398 (2) | 0.0197 (7) | |
| H9BA | 0.4278 | 0.2407 | 0.6562 | 0.024* | |
| C10B | 0.5212 (2) | 0.3334 (2) | 0.6183 (2) | 0.0183 (7) | |
| C11B | 0.6066 (3) | 0.3310 (2) | 0.5956 (2) | 0.0219 (7) | |
| H11B | 0.6321 | 0.3950 | 0.5823 | 0.026* | |
| C12B | 0.6525 (3) | 0.2323 (2) | 0.5929 (2) | 0.0242 (7) | |
| H12B | 0.7094 | 0.2303 | 0.5776 | 0.029* | |
| C13B | 0.4722 (3) | 0.4381 (3) | 0.6207 (2) | 0.0222 (7) | |
| H2NA | 0.999 (3) | 0.077 (3) | 0.366 (2) | 0.028 (9)* | |
| H1NA | 0.996 (3) | 0.199 (3) | 0.365 (3) | 0.048 (12)* | |
| H2NB | 0.527 (3) | −0.184 (3) | 0.654 (2) | 0.044 (11)* | |
| H1NB | 0.538 (3) | −0.311 (3) | 0.675 (2) | 0.039 (10)* |
| N1A | 0.0241 (14) | 0.0159 (14) | 0.0297 (13) | −0.0010 (11) | 0.0180 (12) | 0.0011 (11) |
| N2A | 0.0128 (12) | 0.0135 (14) | 0.0182 (11) | 0.0012 (10) | 0.0089 (10) | 0.0005 (9) |
| N3A | 0.0293 (16) | 0.0154 (17) | 0.0494 (17) | 0.0009 (13) | 0.0290 (14) | −0.0006 (13) |
| N4A | 0.0240 (14) | 0.0166 (15) | 0.0305 (13) | 0.0020 (11) | 0.0173 (12) | 0.0021 (11) |
| C1A | 0.0197 (15) | 0.0196 (18) | 0.0157 (13) | −0.0026 (12) | 0.0097 (12) | −0.0022 (12) |
| C2A | 0.0239 (16) | 0.0113 (17) | 0.0263 (15) | −0.0020 (13) | 0.0152 (13) | 0.0005 (12) |
| C3A | 0.0225 (16) | 0.0148 (17) | 0.0260 (15) | −0.0034 (13) | 0.0140 (13) | 0.0002 (12) |
| C4A | 0.0154 (15) | 0.0197 (18) | 0.0203 (14) | 0.0019 (12) | 0.0103 (13) | −0.0010 (12) |
| C5A | 0.0153 (14) | 0.0134 (16) | 0.0165 (13) | 0.0020 (12) | 0.0082 (12) | −0.0009 (11) |
| C6A | 0.0141 (14) | 0.0202 (18) | 0.0179 (13) | 0.0025 (12) | 0.0094 (12) | −0.0004 (12) |
| C7A | 0.0119 (13) | 0.0140 (16) | 0.0130 (12) | −0.0016 (11) | 0.0053 (11) | 0.0002 (11) |
| C8A | 0.0216 (15) | 0.0155 (17) | 0.0191 (14) | 0.0006 (12) | 0.0113 (13) | −0.0034 (12) |
| C9A | 0.0213 (16) | 0.0210 (18) | 0.0226 (14) | −0.0014 (13) | 0.0149 (13) | −0.0006 (12) |
| C10A | 0.0147 (14) | 0.0136 (16) | 0.0161 (13) | 0.0008 (12) | 0.0073 (12) | 0.0008 (11) |
| C11A | 0.0171 (15) | 0.0163 (17) | 0.0209 (14) | 0.0033 (12) | 0.0101 (13) | −0.0015 (12) |
| C12A | 0.0151 (14) | 0.0175 (17) | 0.0209 (14) | 0.0008 (12) | 0.0121 (12) | −0.0004 (12) |
| C13A | 0.0169 (15) | 0.0178 (17) | 0.0178 (14) | 0.0000 (13) | 0.0102 (12) | 0.0006 (12) |
| C3B | 0.0184 (15) | 0.0199 (18) | 0.0216 (15) | −0.0007 (12) | 0.0109 (13) | −0.0029 (12) |
| N2B | 0.0195 (13) | 0.0145 (15) | 0.0220 (12) | 0.0044 (10) | 0.0124 (11) | 0.0027 (10) |
| N3B | 0.0266 (15) | 0.0137 (17) | 0.0392 (15) | 0.0009 (13) | 0.0239 (13) | 0.0023 (12) |
| N4B | 0.0262 (14) | 0.0168 (16) | 0.0405 (15) | 0.0033 (12) | 0.0206 (13) | 0.0012 (12) |
| C1B | 0.0094 (13) | 0.0216 (18) | 0.0130 (13) | −0.0003 (12) | 0.0040 (11) | 0.0003 (11) |
| C2B | 0.0182 (15) | 0.0154 (17) | 0.0218 (14) | 0.0008 (12) | 0.0103 (13) | 0.0033 (12) |
| N1B | 0.0213 (14) | 0.0181 (15) | 0.0310 (13) | 0.0015 (11) | 0.0166 (12) | −0.0030 (11) |
| C4B | 0.0260 (16) | 0.0171 (18) | 0.0287 (15) | −0.0014 (13) | 0.0169 (14) | 0.0023 (13) |
| C5B | 0.0126 (14) | 0.0164 (17) | 0.0142 (13) | 0.0026 (11) | 0.0060 (11) | −0.0008 (11) |
| C6B | 0.0220 (15) | 0.0198 (18) | 0.0285 (15) | 0.0034 (13) | 0.0193 (13) | 0.0038 (13) |
| C7B | 0.0137 (14) | 0.0169 (17) | 0.0163 (13) | −0.0002 (12) | 0.0087 (12) | −0.0007 (11) |
| C8B | 0.0206 (16) | 0.0141 (17) | 0.0195 (14) | −0.0015 (12) | 0.0120 (13) | 0.0015 (11) |
| C9B | 0.0192 (15) | 0.0211 (18) | 0.0238 (14) | −0.0015 (13) | 0.0152 (13) | 0.0001 (12) |
| C10B | 0.0188 (15) | 0.0151 (17) | 0.0168 (13) | 0.0004 (12) | 0.0077 (12) | −0.0021 (11) |
| C11B | 0.0264 (16) | 0.0172 (18) | 0.0264 (15) | −0.0005 (13) | 0.0175 (14) | −0.0001 (12) |
| C12B | 0.0269 (17) | 0.0200 (18) | 0.0345 (17) | 0.0018 (13) | 0.0227 (15) | 0.0034 (13) |
| C13B | 0.0192 (15) | 0.0229 (19) | 0.0246 (15) | −0.0025 (14) | 0.0124 (13) | 0.0000 (13) |
| N1A—C3A | 1.343 (3) | C3B—N1B | 1.354 (3) |
| N1A—C4A | 1.343 (3) | C3B—C2B | 1.379 (4) |
| N2A—C6A | 1.281 (3) | C3B—H3BA | 0.9300 |
| N2A—C5A | 1.413 (3) | N2B—C6B | 1.267 (3) |
| N3A—C1A | 1.354 (4) | N2B—C5B | 1.411 (3) |
| N3A—H2NA | 0.93 (3) | N3B—C1B | 1.366 (4) |
| N3A—H1NA | 0.88 (4) | N3B—H2NB | 0.88 (4) |
| N4A—C13A | 1.143 (3) | N3B—H1NB | 0.90 (4) |
| C1A—C2A | 1.399 (4) | N4B—C13B | 1.147 (4) |
| C1A—C5A | 1.422 (4) | C1B—C2B | 1.391 (4) |
| C2A—C3A | 1.381 (4) | C1B—C5B | 1.415 (4) |
| C2A—H2AA | 0.9300 | C2B—H2BA | 0.9300 |
| C3A—H3AA | 0.9300 | N1B—C4B | 1.336 (4) |
| C4A—C5A | 1.392 (4) | C4B—C5B | 1.393 (4) |
| C4A—H4AA | 0.9300 | C4B—H4BA | 0.9300 |
| C6A—C7A | 1.466 (4) | C6B—C7B | 1.461 (4) |
| C6A—H6AA | 0.9300 | C6B—H6BA | 0.9300 |
| C7A—C12A | 1.389 (4) | C7B—C12B | 1.396 (4) |
| C7A—C8A | 1.406 (4) | C7B—C8B | 1.399 (4) |
| C8A—C9A | 1.370 (4) | C8B—C9B | 1.390 (4) |
| C8A—H8AA | 0.9300 | C8B—H8BA | 0.9300 |
| C9A—C10A | 1.402 (4) | C9B—C10B | 1.394 (4) |
| C9A—H9AA | 0.9300 | C9B—H9BA | 0.9300 |
| C10A—C11A | 1.398 (4) | C10B—C11B | 1.393 (4) |
| C10A—C13A | 1.437 (4) | C10B—C13B | 1.458 (4) |
| C11A—C12A | 1.379 (4) | C11B—C12B | 1.375 (4) |
| C11A—H11A | 0.9300 | C11B—H11B | 0.9300 |
| C12A—H12A | 0.9300 | C12B—H12B | 0.9300 |
| C3A—N1A—C4A | 114.9 (2) | N1B—C3B—C2B | 124.1 (3) |
| C6A—N2A—C5A | 120.6 (2) | N1B—C3B—H3BA | 117.9 |
| C1A—N3A—H2NA | 121.2 (19) | C2B—C3B—H3BA | 117.9 |
| C1A—N3A—H1NA | 123 (2) | C6B—N2B—C5B | 121.8 (2) |
| H2NA—N3A—H1NA | 112 (3) | C1B—N3B—H2NB | 115 (2) |
| N3A—C1A—C2A | 121.7 (3) | C1B—N3B—H1NB | 115 (2) |
| N3A—C1A—C5A | 121.2 (3) | H2NB—N3B—H1NB | 125 (3) |
| C2A—C1A—C5A | 117.0 (3) | N3B—C1B—C2B | 122.7 (3) |
| C3A—C2A—C1A | 119.9 (3) | N3B—C1B—C5B | 120.4 (3) |
| C3A—C2A—H2AA | 120.0 | C2B—C1B—C5B | 116.8 (3) |
| C1A—C2A—H2AA | 120.0 | C3B—C2B—C1B | 120.2 (3) |
| N1A—C3A—C2A | 124.6 (3) | C3B—C2B—H2BA | 119.9 |
| N1A—C3A—H3AA | 117.7 | C1B—C2B—H2BA | 119.9 |
| C2A—C3A—H3AA | 117.7 | C4B—N1B—C3B | 115.3 (3) |
| N1A—C4A—C5A | 126.3 (3) | N1B—C4B—C5B | 125.4 (3) |
| N1A—C4A—H4AA | 116.9 | N1B—C4B—H4BA | 117.3 |
| C5A—C4A—H4AA | 116.9 | C5B—C4B—H4BA | 117.3 |
| C4A—C5A—N2A | 126.5 (3) | C4B—C5B—N2B | 125.6 (3) |
| C4A—C5A—C1A | 117.2 (3) | C4B—C5B—C1B | 118.2 (3) |
| N2A—C5A—C1A | 116.2 (2) | N2B—C5B—C1B | 116.2 (2) |
| N2A—C6A—C7A | 121.0 (2) | N2B—C6B—C7B | 122.8 (3) |
| N2A—C6A—H6AA | 119.5 | N2B—C6B—H6BA | 118.6 |
| C7A—C6A—H6AA | 119.5 | C7B—C6B—H6BA | 118.6 |
| C12A—C7A—C8A | 119.3 (3) | C12B—C7B—C8B | 118.8 (3) |
| C12A—C7A—C6A | 119.3 (2) | C12B—C7B—C6B | 120.0 (2) |
| C8A—C7A—C6A | 121.3 (3) | C8B—C7B—C6B | 121.2 (3) |
| C9A—C8A—C7A | 120.2 (3) | C9B—C8B—C7B | 120.4 (3) |
| C9A—C8A—H8AA | 119.9 | C9B—C8B—H8BA | 119.8 |
| C7A—C8A—H8AA | 119.9 | C7B—C8B—H8BA | 119.8 |
| C8A—C9A—C10A | 120.3 (3) | C8B—C9B—C10B | 119.2 (3) |
| C8A—C9A—H9AA | 119.8 | C8B—C9B—H9BA | 120.4 |
| C10A—C9A—H9AA | 119.8 | C10B—C9B—H9BA | 120.4 |
| C11A—C10A—C9A | 119.6 (3) | C11B—C10B—C9B | 121.0 (3) |
| C11A—C10A—C13A | 119.7 (3) | C11B—C10B—C13B | 118.9 (3) |
| C9A—C10A—C13A | 120.7 (3) | C9B—C10B—C13B | 120.1 (3) |
| C12A—C11A—C10A | 119.8 (3) | C12B—C11B—C10B | 118.9 (3) |
| C12A—C11A—H11A | 120.1 | C12B—C11B—H11B | 120.5 |
| C10A—C11A—H11A | 120.1 | C10B—C11B—H11B | 120.5 |
| C11A—C12A—C7A | 120.8 (3) | C11B—C12B—C7B | 121.6 (3) |
| C11A—C12A—H12A | 119.6 | C11B—C12B—H12B | 119.2 |
| C7A—C12A—H12A | 119.6 | C7B—C12B—H12B | 119.2 |
| N4A—C13A—C10A | 178.6 (3) | N4B—C13B—C10B | 178.8 (3) |
| N3A—C1A—C2A—C3A | −179.5 (3) | N1B—C3B—C2B—C1B | 0.1 (4) |
| C5A—C1A—C2A—C3A | 0.1 (4) | N3B—C1B—C2B—C3B | −178.8 (2) |
| C4A—N1A—C3A—C2A | 0.2 (4) | C5B—C1B—C2B—C3B | −0.7 (4) |
| C1A—C2A—C3A—N1A | −0.3 (4) | C2B—C3B—N1B—C4B | 0.4 (4) |
| C3A—N1A—C4A—C5A | −0.1 (4) | C3B—N1B—C4B—C5B | −0.3 (4) |
| N1A—C4A—C5A—N2A | 177.7 (2) | N1B—C4B—C5B—N2B | 179.8 (2) |
| N1A—C4A—C5A—C1A | 0.0 (4) | N1B—C4B—C5B—C1B | −0.3 (4) |
| C6A—N2A—C5A—C4A | 15.3 (4) | C6B—N2B—C5B—C4B | 0.4 (4) |
| C6A—N2A—C5A—C1A | −167.0 (2) | C6B—N2B—C5B—C1B | −179.5 (2) |
| N3A—C1A—C5A—C4A | 179.6 (2) | N3B—C1B—C5B—C4B | 178.9 (2) |
| C2A—C1A—C5A—C4A | −0.1 (3) | C2B—C1B—C5B—C4B | 0.7 (4) |
| N3A—C1A—C5A—N2A | 1.7 (4) | N3B—C1B—C5B—N2B | −1.1 (4) |
| C2A—C1A—C5A—N2A | −178.0 (2) | C2B—C1B—C5B—N2B | −179.3 (2) |
| C5A—N2A—C6A—C7A | −179.3 (2) | C5B—N2B—C6B—C7B | −179.1 (2) |
| N2A—C6A—C7A—C12A | −179.0 (2) | N2B—C6B—C7B—C12B | 178.9 (3) |
| N2A—C6A—C7A—C8A | −1.2 (4) | N2B—C6B—C7B—C8B | −0.9 (4) |
| C12A—C7A—C8A—C9A | −0.7 (4) | C12B—C7B—C8B—C9B | 0.3 (4) |
| C6A—C7A—C8A—C9A | −178.5 (2) | C6B—C7B—C8B—C9B | −179.9 (2) |
| C7A—C8A—C9A—C10A | 0.5 (4) | C7B—C8B—C9B—C10B | 0.6 (4) |
| C8A—C9A—C10A—C11A | −0.4 (4) | C8B—C9B—C10B—C11B | −1.2 (4) |
| C8A—C9A—C10A—C13A | −179.9 (2) | C8B—C9B—C10B—C13B | 179.5 (2) |
| C9A—C10A—C11A—C12A | 0.4 (4) | C9B—C10B—C11B—C12B | 1.0 (4) |
| C13A—C10A—C11A—C12A | 179.9 (2) | C13B—C10B—C11B—C12B | −179.7 (2) |
| C10A—C11A—C12A—C7A | −0.5 (4) | C10B—C11B—C12B—C7B | −0.1 (4) |
| C8A—C7A—C12A—C11A | 0.7 (4) | C8B—C7B—C12B—C11B | −0.5 (4) |
| C6A—C7A—C12A—C11A | 178.6 (2) | C6B—C7B—C12B—C11B | 179.7 (3) |
| H··· | ||||
| N3A—H2NA···N4Ai | 0.92 (4) | 2.26 (4) | 3.155 (4) | 165 (3) |
| N3A—H1NA···N1Bii | 0.89 (4) | 2.33 (5) | 3.080 (4) | 143 (4) |
| N3B—H2NB···N1Aiii | 0.89 (4) | 2.42 (4) | 3.112 (4) | 136 (4) |
| N3B—H1NB···N4Bi | 0.90 (4) | 2.36 (4) | 3.220 (4) | 159 (2) |
Hydrogen-bond geometry (Å, °)
| H⋯ | ||||
|---|---|---|---|---|
| N3 | 0.92 (4) | 2.26 (4) | 3.155 (4) | 165 (3) |
| N3 | 0.89 (4) | 2.33 (5) | 3.080 (4) | 143 (4) |
| N3 | 0.89 (4) | 2.42 (4) | 3.112 (4) | 136 (4) |
| N3 | 0.90 (4) | 2.36 (4) | 3.220 (4) | 159 (2) |
Symmetry codes: (i) ; (ii) ; (iii) .