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Volume 70 
Part 2 
Pages 210-215  
February 2014  

Received 7 November 2013
Accepted 30 December 2013
Online 11 January 2014

Comparison of N-(3,4,5-tri­meth­oxy­benzyl­idene)naphthalen-1-amine and its reduction product N-(3,4,5-tri­meth­oxy­benzyl)naphthalen-1-amine

aDepartamento de Química, Universidad de Valle, AA 25360 Cali, Colombia,bDepartamento de Química Inorgánica y Orgánica, Universidad de Jaén, 23071 Jaén, Spain, and cSchool of Chemistry, University of St Andrews, Fife KY16 9ST, Scotland
Correspondence e-mail: cg@st-andrews.ac.uk

The mol­ecules in (E)-N-(3,4,5-tri­meth­oxy­benzyl­idene)naph­thalen-1-amine, C20H19NO3, (I), and its reduction product N-(3,4,5-tri­meth­oxy­benzyl)naphthalen-1-amine, C20H21NO3, (II), are both conformationally chiral, but (I) crystallizes in a centrosymmetric space group, while (II) crystallizes with just one conformational enantio­mer in each crystal. A combination of two C-H...O hydrogen bonds links the mol­ecules of (I) into sheets containing a single type of R66(44) ring, and these sheets are linked into a continuous three-dimensional array by a single [pi]-[pi] stacking inter­action. The mol­ecules of (II) are linked into complex sheets by a combination of N-H...O, C-H...O and C-H...[pi](arene) hydrogen bonds.

1. Introduction

We report here the mol­ecular and supra­molecular structures of (E)-N-(3,4,5-tri­meth­oxy­benzyl­idene)naphthalen-1-amine, (I)[link] (Fig. 1[link]), and its reduction product N-(3,4,5-tri­meth­oxy­benzyl)naphthalen-1-amine, (II)[link] (Fig. 2[link]). Compound (I)[link] was prepared using a thermal condensation reaction between 1-naphthyl­amine and 3,4,5-tri­meth­oxy­benzaldehyde, and (II)[link] was prepared from (I)[link] by reduction with sodium borohydride.

[Figure 1]
Figure 1
The mol­ecular structure of (I)[link], showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
[Figure 2]
Figure 2
The mol­ecular structure of (II)[link], showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
[Figure 3]
Figure 3
Part of the crystal structure of (I)[link], showing the formation of a hydrogen-bonded C(7) chain parallel to [010]. Dashed lines indicate hydrogen bonds. For the sake of clarity, H atoms not involved in the motif shown have been omitted. Atoms marked with an asterisk (*) or a hash symbol (#) are at the symmetry positions (-x + [{1\over 2}], y + [{1\over 2}], -z + [{1\over 2}]) and (-x + [{1\over 2}], y - [{1\over 2}], -z + [{1\over 2}]), respectively.
[Figure 4]
Figure 4
Part of the crystal structure of (I)[link], showing the formation of a hydrogen-bonded C(11) chain parallel to [110]. Dashed lines indicate hydrogen bonds. For the sake of clarity, H atoms not involved in the motif shown have been omitted. Atoms marked with an asterisk (*) or a hash symbol (#) are at the symmetry positions (x + 1, y + 1, z) and (x - 1, y - 1, z), respectively.
[Figure 5]
Figure 5
A stereoview of part of the crystal structure of (I)[link], showing the formation of a hydrogen-bonded sheet of R66(44) rings parallel to (001). Dashed lines indicate hydrogen bonds. For the sake of clarity, H atoms not involved in the motifs shown have been omitted.
[Figure 6]
Figure 6
Part of the crystal structure of (I)[link], showing the formation of the [pi]-[pi] stacking inter­action which links adjacent hydrogen-bonded sheets. For the sake of clarity, all H atoms have been omitted. The atom marked with an asterisk (*) is at the symmetry position (-x + 2, -y + 1, -z + 1).
[Figure 7]
Figure 7
Part of the crystal structure of (II)[link], showing the formation of a hydrogen-bonded C(5)C(7)[R22(10)] chain of rings parallel to [010]. Dashed lines indicate hydrogen bonds. For the sake of clarity, H atoms not involved in the motif shown have been omitted. Atoms marked with an asterisk (*) or a hash symbol (#) are at the symmetry positions (-x + 1, y + [{1\over 2}], -z + [{1\over 2}]) and (-x + 1, y - [{1\over 2}], -z + [{1\over 2}]), respectively.
[Figure 8]
Figure 8
A stereoview of part of the crystal structure of (II)[link], showing the formation of a hydrogen-bonded sheet parallel to (001). Dashed lines indicate hydrogen bonds. For the sake of clarity, H atoms not involved in the motifs shown have been omitted.

2. Experimental

2.1. Synthesis and crystallization

For the synthesis of (I)[link], a mixture of 1-naphthyl­amine (2.1 mmol) and 3,4,5-tri­meth­oxy­benzaldehyde (2.1 mmol) was heated in an oil bath at 423 K for 8 min until complete disappearance of the starting materials, as monitored by thin-layer chromatography (TLC). The mixture was cooled to ambient temperature and the resulting brown solid was triturated with ethanol to afford the title compound, (I)[link], as brown crystals (yield 86%; m.p. 402 K). FT-IR (KBr, [nu], cm-1): 3015, 2991, 2953, 2932, 2831, 1618 (C=N), 1578 (C=C), 1502, 1331, 1227 (C-O), 1130 (C-O), 772.

For the synthesis of (II)[link], a twofold molar excess of sodium borohydride was added in portions over a period of 15 min to a solution of (I)[link] (0.400 g) in ethanol (12 ml). After complete disappearance of the starting compound, (I)[link], as monitored by TLC, the solvent was removed under reduced pressure, an excess of water was added and the product was exhaustively extracted with ethyl acetate. The combined organic extracts were dried using anhydrous sodium sulfate. The drying agent was then removed by filtration and the solvent removed under reduced pressure to afford (II)[link] as pale-yellow crystals (yield 98%; m.p. 412 K). FT-IR (KBr, [nu], cm-1): 3413 (N-H), 3004, 2933, 2836, 1586 (C=C), 1532, 1504, 1237 (C-O), 1114 (C-O), 1005, 778.

[Scheme 1]

Crystals of (I)[link] and (II)[link] suitable for single-crystal X-ray diffraction were grown by slow evaporation, at ambient temperature and in air, of the corresponding solutions in methanol.

2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1[link]. All H atoms were located in difference maps and were then treated as riding. C-bound H atoms were permitted to ride in geometrically idealized positions, with C-H = 0.95 (aromatic and alkenyl), 0.98 (CH3) or 0.99 Å (CH2) and Uiso(H) = kUeq(C), where k = 1.5 for the methyl groups, which were permitted to rotate but not to tilt, and k = 1.2 for all other C-bound H atoms. The H atom bonded to atom N1 in (II)[link] was permitted to ride at the position located in a difference map, with Uiso(H) = 1.2Ueq(N), giving an N-H distance of 0.97 Å. Several low-angle reflections, viz. (101) in (I)[link] and (101) and (002) in (II)[link], which had been wholly or partially attenuated by the beam-stop, were omitted from the data sets. In the absence of significant resonant scattering, the Flack x parameter (Flack, 1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]) for (II)[link] was indeterminate (Flack & Bernardinelli, 2000[Flack, H. D. & Bernardinelli, G. (2000). J. Appl. Cryst. 33, 1143-1148.]); accordingly, the Friedel-equivalent reflections for (II)[link] were merged prior to the final refinements. It was not possible, therefore, to determine the absolute configuration of the mol­ecule in the crystal of (II)[link] selected for data collection. The reference mol­ecule for (II)[link] was selected to have the same sign for the C13-C14-O14-C24 torsion angle as that in the reference mol­ecule for (I)[link].

3. Results and discussion

Despite their similar mol­ecular constitutions, (I)[link] and (II)[link] crystallize in very different space groups, viz. the centrosymmetric monoclinic space group P21/n in the case of (I)[link] and the Sohnke ortho­rhom­bic space group P212121 in the case of (II)[link]. Both compounds crystallize with Z = 4 in unit cells of very similar volume, although it is perhaps surprising that the unit-cell volume for (I)[link] is marginally greater than that for (II)[link], presumably reflecting the stronger inter­molecular hydrogen-bonding in (II)[link] (see below). Consistent with this, the density of (II)[link] (1.296 Mg m-3) is slightly greater than that of (I)[link] (1.283 Mg m-3).

In neither compound are the ring systems exactly coplanar with the central C-N-C-C linking unit, as indicated by the leading torsion angles (Tables 2[link] and 3[link]). The torsion angle defining the orientation of the trimethoxyphenyl ring with respect to the central spacer unit in compound (I)[link] is close to zero, but there is no metrical evidence for any electronic delocalization across the spacer unit. The dihedral angle between the tris­ubstituted aryl ring and the naphthalene system in (I)[link] is 55.4 (2)°, whereas in (II)[link] this angle is 88.2 (2)°. In both compounds, atom C24 of the 4-meth­oxy substituent is considerably displaced from the plane of the adjacent aryl ring, by 1.224 (3) Å in (I)[link] and 1.018 (3) Å in (II)[link]. A conformation having atom C24 nearly coplanar with the adjacent aryl ring is precluded by the steric congestion between atom C24 and atoms O13 or O15 which would thereby result. Similar conformations have been observed in other 3,4,5-tri­meth­oxy­phenyl derivatives (Trilleras et al., 2005[Trilleras, J., Quiroga, J., Cobo, J., Low, J. N. & Glidewell, C. (2005). Acta Cryst. C61, o414-o416.]; Peralta et al., 2007[Peralta, M. A., de Souza, M. N. V., Wardell, S. M. S. V., Wardell, J. L., Low, J. N. & Glidewell, C. (2007). Acta Cryst. C63, o68-o72.]; Cuervo et al., 2009[Cuervo, P., Abonía, R., Cobo, J. & Glidewell, C. (2009). Acta Cryst. C65, o326-o330.]). For compound (II)[link], the torsion angles (Table 3[link]) indicate considerable deviation from planarity for atoms C23 and C25 of the 3-meth­oxy and 5-meth­oxy substituents, which are displaced from the plane of the adjacent ring by 0.252 (3) and 0.468 (3) Å, respectively, as opposed to displacements of only 0.043 (3) and 0.128 (3) Å, respectively, in (I)[link]. However, in both compounds, the two C-C-O angles at atom C14 have fairly similar values, whereas the corresponding pairs of values at atoms C13 and C15 differ by ca 10° (Tables 2[link] and 3[link]), as typically found (Seip & Seip, 1973[Seip, H. M. & Seip, R. (1973). Acta Chem. Scand. 27, 4024-4027.]; Ferguson et al., 1996[Ferguson, G., Glidewell, C. & Patterson, I. L. J. (1996). Acta Cryst. C52, 420-423.]) for methoxyaryl systems in which the meth­oxy C atom is effectively coplanar with the adjacent aryl ring. The N1-C17 distances are clearly consistent with the different oxidation levels in (I)[link] and (II)[link], and it is inter­esting to note the relative values of the bond angles at atoms N1 and C17, but no simple rationalization for this is possible.

The mol­ecules of (I)[link] and (II)[link] exhibit no inter­nal symmetry and hence they are both conformationally chiral. No evidence for twinning was found for compound (II)[link] and, in the absence of inversion or reflection twinning, each crystal can contain only one conformational enantiomer. There is no reason to suppose that one conformational enantiomer is preferred over the other, and hence it seems likely that compound (II)[link] crystallizes as a conformational conglomerate, while com­pound (I)[link] crystallizes as a conformational racemate.

The mol­ecules of (I)[link] are linked into a three-dimensional array in the form of [pi]-stacked hydrogen-bonded sheets. The sheets are built using two C-H...O hydrogen bonds (Table 4[link]) and their formation is readily analysed in terms of two one-dimensional substructures (Ferguson et al., 1998a[Ferguson, G., Glidewell, C., Gregson, R. M. & Meehan, P. R. (1998a). Acta Cryst. B54, 129-138.],b[Ferguson, G., Glidewell, C., Gregson, R. M. & Meehan, P. R. (1998b). Acta Cryst. B54, 139-150.]; Gregson et al., 2000[Gregson, R. M., Glidewell, C., Ferguson, G. & Lough, A. J. (2000). Acta Cryst. B56, 39-57.]). Mol­ecules related by the 21 screw axis along ([{1 \over 4}]y[{1 \over 4}]) are linked by the shorter hydrogen bond to form a C(7) chain (Bernstein et al., 1995[Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555-1573.]) running parallel to the [010] direction (Fig. 3[link]). In addition, mol­ecules related by translation are linked by the longer of the two hydrogen bonds to form a C(11) chain running parallel to the [110] direction (Fig. 4[link]). The combination of chains along [010] and [110] generates a sheet lying parallel to (001) and built from a single type of R66(44) ring (Fig. 5[link]).

Two sheets of this type, related to one another by inversion, pass through each unit cell, in the domains 0 < z < [{1 \over 2}] and [{1 \over 2}] < z < 1.0, respectively, and all of the sheets are linked into a three-dimensional structure by the action of a single aromatic [pi]-[pi] stacking inter­action. The C5-C10 rings in the mol­ecules at (x, y, z) and (-x + 2, -y + 1, -z + 1), which lie in different hydrogen-bonded sheets, are strictly parallel, with an inter­planar spacing of 3.480 (2) Å; the ring-centroid separation is 3.798 (2) Å, corresponding to a near-ideal ring-centroid offset of 1.521 (2) Å (Fig. 6[link]). Propagation of this inter­action by the space-group symmetry operators is sufficient to link all of the hydrogen-bonded sheets.

There are four independent hydrogen bonds in the crystal structure of (II)[link] (Table 5[link]), including an N-H...O hydrogen bond, which is necessarily absent from the structure of (I)[link]. However, despite the large number of hydrogen bonds in (II)[link], the supra­molecular assembly is only two-dimensional. The overall sheet structure is of considerable complexity but, as in (I)[link], its formation can be analysed in terms of simple substructures. The N-H...O hydrogen bond links mol­ecules related by the 21 screw axis along ([{1 \over 2}], y, [{1 \over 4}]) into a C(7) chain running parallel to the [010] direction, and this chain formation is enhanced by a rather long, but nearly linear, C-H...O hydrogen bond which forms a C(5) motif, so that these two inter­actions together generate a C(5)C(7)[R22(10)] chain of rings (Fig. 7[link]).

This chain of rings actually lies within a sheet generated by the two C-H...[pi](arene) hydrogen bonds. The inter­action having atom C4 as the donor links mol­ecules related by translation into a chain running parallel to the [100] direction, while that involving atom C7 as the donor links mol­ecules related by the 21 screw axis along (0, y, [{1 \over 4}]) into a chain running parallel to the [010] direction. In combination, these two chains generate a sheet lying parallel to (001) (Fig. 8[link]). Two sheets pass through each unit cell, in the domains 0 < z < [{1 \over 2}] and [{1 \over 2}] < z < 1.0, and containing screw axes at z = [{1 \over 4}] and z = [{3 \over 4}], respectively. The only possible direction-specific inter­action between mol­ecules in adjacent sheets is a C-H...[pi](arene) contact, which not only involves a C-H bond of low acidity but is characterized by a rather long H...A distance, 2.94 Å, so that this contact is unlikely to be structurally significant.

Table 1
Experimental details

  (I) (II)
Crystal data
Chemical formula C20H19NO3 C20H21NO3
Mr 321.36 323.38
Crystal system, space group Monoclinic, P21/n Orthorhombic, P212121
Temperature (K) 120 120
a, b, c (Å) 8.9697 (11), 9.3300 (9), 19.9254 (12) 9.4460 (17), 11.0868 (18), 15.8195 (16)
[alpha], [beta], [gamma] (°) 90, 93.846 (8), 90 90, 90, 90
V3) 1663.8 (3) 1656.7 (4)
Z 4 4
Radiation type Mo K[alpha] Mo K[alpha]
[mu] (mm-1) 0.09 0.09
Crystal size (mm) 0.29 × 0.28 × 0.20 0.41 × 0.39 × 0.32
 
Data collection
Diffractometer Bruker-Nonius KappaCCD area-detector diffrac­tom­eter Bruker-Nonius KappaCCD area-detector diffrac­tom­eter
Absorption correction Multi-scan (SADABS; Sheldrick, 2003[Sheldrick, G. M. (2003). SADABS. University of Göttingen, Germany.]) Multi-scan (SADABS; Sheldrick, 2003[Sheldrick, G. M. (2003). SADABS. University of Göttingen, Germany.])
Tmin, Tmax 0.958, 0.983 0.955, 0.973
No. of measured, independent and observed [I > 2[sigma](I)] reflections 23021, 3820, 2117 16040, 2168, 1799
Rint 0.070 0.078
(sin [theta]/[lambda])max-1) 0.650 0.650
 
Refinement
R[F2 > 2[sigma](F2)], wR(F2), S 0.060, 0.170, 1.02 0.042, 0.105, 1.09
No. of reflections 3820 2168
No. of parameters 220 220
H-atom treatment H-atom parameters constrained H-atom parameters constrained
[Delta][rho]max, [Delta][rho]min (e Å-3) 0.29, -0.28 0.21, -0.18
Computer programs: COLLECT (Nonius, 1999[Nonius (1999). COLLECT. Nonius BV, Delft, The Netherlands.]), DIRAX/LSQ (Duisenberg et al., 2000[Duisenberg, A. J. M., Hooft, R. W. W., Schreurs, A. M. M. & Kroon, J. (2000). J. Appl. Cryst. 33, 893-898.]), EVALCCD (Duisenberg et al., 2003[Duisenberg, A. J. M., Kroon-Batenburg, L. M. J. & Schreurs, A. M. M. (2003). J. Appl. Cryst. 36, 220-229.]), SIR2004 (Burla et al., 2005[Burla, M. C., Caliandro, R., Camalli, M., Carrozzini, B., Cascarano, G. L., De Caro, L., Giacovazzo, C., Polidori, G. & Spagna, R. (2005). J. Appl. Cryst. 38, 381-388.]), SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]) and PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]).

Table 2
Selected geometric parameters (Å, °) for (I)[link]

N1-C17 1.280 (2)    
       
C1-N1-C17 117.48 (18) O14-C14-C13 119.71 (19)
N1-C17-C11 122.34 (19) O14-C14-C15 120.35 (18)
O13-C13-C12 125.09 (19) O15-C15-C14 115.33 (19)
O13-C13-C14 114.47 (19) O15-C15-C16 124.92 (19)
       
C2-C1-N1-C17 -46.8 (3) C12-C13-O13-C23 2.8 (3)
C1-N1-C17-C11 179.99 (19) C13-C14-O14-C24 90.8 (2)
N1-C17-C11-C12 -8.7 (3) C16-C15-O15-C25 8.6 (3)

Table 3
Selected geometric parameters (Å, °) for (II)[link]

N1-C17 1.443 (3)    
       
C1-N1-C17 122.3 (2) O14-C14-C13 117.6 (2)
N1-C17-C11 116.8 (2) O14-C14-C15 122.8 (2)
O13-C13-C12 124.2 (2) O15-C15-C14 116.2 (2)
O13-C13-C14 115.0 (2) O15-C15-C16 123.9 (2)
       
C2-C1-N1-C17 -5.3 (4) C12-C13-O13-C23 10.2 (3)
C1-N1-C17-C11 73.6 (3) C13-C14-O14-C24 126.2 (2)
N1-C17-C11-C12 33.4 (3) C16-C15-O15-C25 -26.3 (4)

Table 4
Hydrogen-bond geometry (Å, °) for (I)[link]

D-H...A D-H H...A D...A D-H...A
C5-H5...O13i 0.95 2.52 3.454 (3) 169
C17-H17...O14ii 0.95 2.40 3.331 (2) 166
Symmetry codes: (i) x+1, y+1, z; (ii) [-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{1\over 2}}].

Table 5
Hydrogen-bond geometry (Å, °) for (II)[link]

Cg1 represents the centroid of the C11-C16 ring and Cg2 represents the centroid of the C1-C4/C10/C9 ring.

D-H...A D-H H...A D...A D-H...A
N1-H1...O13i 0.97 2.07 3.016 (3) 163
C12-H12...O14i 0.95 2.59 3.535 (3) 176
C4-H4...Cg1ii 0.95 2.69 3.632 (3) 173
C7-H7...Cg2iii 0.95 2.86 3.677 (3) 145
Symmetry codes: (i) [-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]; (ii) x-1, y, z; (iii) [-x, y+{\script{1\over 2}}, -z+{\script{1\over 2}}].

Supporting information for this paper is available from the IUCr electronic archives (Reference: SF3215 ).


Acknowledgements

The authors thank the Centro de Instrumentación Científico-Técnica of the Universidad de Jaén and the staff for the data collection. AG and RA thank COLCIENCIAS and the Universidad del Valle for financial support. JC thanks the Consejería de Innovación, Ciencia y Empresa (Junta de Andalucía, Spain) and the Universidad de Jaén for financial support.

References

Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555-1573.  [CrossRef] [ChemPort] [Web of Science]
Burla, M. C., Caliandro, R., Camalli, M., Carrozzini, B., Cascarano, G. L., De Caro, L., Giacovazzo, C., Polidori, G. & Spagna, R. (2005). J. Appl. Cryst. 38, 381-388.  [Web of Science] [CrossRef] [ChemPort] [IUCr Journals]
Cuervo, P., Abonía, R., Cobo, J. & Glidewell, C. (2009). Acta Cryst. C65, o326-o330.  [CSD] [CrossRef] [ChemPort] [IUCr Journals]
Duisenberg, A. J. M., Hooft, R. W. W., Schreurs, A. M. M. & Kroon, J. (2000). J. Appl. Cryst. 33, 893-898.  [Web of Science] [CrossRef] [ChemPort] [IUCr Journals]
Duisenberg, A. J. M., Kroon-Batenburg, L. M. J. & Schreurs, A. M. M. (2003). J. Appl. Cryst. 36, 220-229.  [Web of Science] [CrossRef] [ChemPort] [IUCr Journals]
Ferguson, G., Glidewell, C., Gregson, R. M. & Meehan, P. R. (1998a). Acta Cryst. B54, 129-138.  [Web of Science] [CSD] [CrossRef] [IUCr Journals]
Ferguson, G., Glidewell, C., Gregson, R. M. & Meehan, P. R. (1998b). Acta Cryst. B54, 139-150.  [Web of Science] [CSD] [CrossRef] [IUCr Journals]
Ferguson, G., Glidewell, C. & Patterson, I. L. J. (1996). Acta Cryst. C52, 420-423.  [CSD] [CrossRef] [IUCr Journals]
Flack, H. D. (1983). Acta Cryst. A39, 876-881.  [CrossRef] [IUCr Journals]
Flack, H. D. & Bernardinelli, G. (2000). J. Appl. Cryst. 33, 1143-1148.  [Web of Science] [CrossRef] [ChemPort] [IUCr Journals]
Gregson, R. M., Glidewell, C., Ferguson, G. & Lough, A. J. (2000). Acta Cryst. B56, 39-57.  [Web of Science] [CSD] [CrossRef] [IUCr Journals]
Nonius (1999). COLLECT. Nonius BV, Delft, The Netherlands.
Peralta, M. A., de Souza, M. N. V., Wardell, S. M. S. V., Wardell, J. L., Low, J. N. & Glidewell, C. (2007). Acta Cryst. C63, o68-o72.  [CSD] [CrossRef] [ChemPort] [IUCr Journals]
Seip, H. M. & Seip, R. (1973). Acta Chem. Scand. 27, 4024-4027.  [CrossRef] [ChemPort]
Sheldrick, G. M. (2003). SADABS. University of Göttingen, Germany.
Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.  [CrossRef] [ChemPort] [IUCr Journals]
Spek, A. L. (2009). Acta Cryst. D65, 148-155.  [Web of Science] [CrossRef] [ChemPort] [IUCr Journals]
Trilleras, J., Quiroga, J., Cobo, J., Low, J. N. & Glidewell, C. (2005). Acta Cryst. C61, o414-o416.  [CSD] [CrossRef] [IUCr Journals]


Acta Cryst (2014). C70, 210-215   [ doi:10.1107/S2053229613034839 ]