Solid-State Synthesis of New Diimide Compounds - American

CRYSTAL GROWTH & DESIGN

Solid-State Synthesis of New Diimide Compounds: A Two-Step Reaction Followed by X-ray Powder Diffraction Antonia Neels,* De´borah Gonza´lez Mantero, and Helen Stoeckli-Evans Institute of Microtechnology, UniVersity of Neuchâtel, Jaquet Droz 1, CH-2002 Neuchâtel, Switzerland

2008 VOL. 8, NO. 4 1147–1153

ReceiVed January 21, 2007; ReVised Manuscript ReceiVed NoVember 2, 2007

ABSTRACT: Using X-ray powder diffraction, it has been possible to follow the two-step mechanism of the formation in the solid state of new diimide compounds. By mixing and heating together the R-dicarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid (H4BCTA), with primary aromatic amines, such as R-NH2, where R ) pyrazin-2-yl, pyridin-4-yl, and 2-chloro-pyridin-4-yl, three new pyromellitdiimides (R-IMID) were obtained in an economical manner (i.e., quantitative yield, fast and solventless syntheses). The initial mixing and heating of the acid and amine lead to the formation of the intermediate hydrogen-bonded organic salts. Hydrogen transport from the acid to the amine was shown to have taken place. Further heating led to the formation of the diimides as the result of a condensation reaction. All the compounds were characterized by X-ray powder diffraction (XRPD) techniques. Introduction Solid-state reactions have a special place in synthetic chemistry as they are potentially solvent-free and are attracting considerable interest as a result of sustainability and environmental issues.1 An added advantage is that such reactions often lead to pure products. No side products are obtained, and the problem of solvate formation is nonexistent. Such reactions2 can be activated mechanically (by milling or grinding), thermally (by heating), or photochemically and therefore usually require simple equipments. In solid-state studies, the principal problem is the structural characterization of the products. In recent years, X-ray powder diffraction (XRPD) analysis has developed considerably because of the improvement in X-ray sources and detectors and especially because of the development of the computer programs necessary to interpret the data.3 XRPD is now an extremely useful technique for characterizing such microcrystalline products, which are often highly insoluble compounds,4 and studying phase transformation processes.5 In the search for new spacer ligands for the construction of functional metal-organic frameworks, we investigated the synthesis of symmetric diimide ligands using solid state reactions that were followed by XRPD. An interesting mechanism was found; namely, the breaking and forming of hydrogen bonds and covalent bonds in a “one pot-two step” manner (Scheme 1). The acid (A) and the base (B), each characterized by their own set of intra and intermolecular hydrogen bonds, were ground together and heated. An intermediate organic salt, A-B+, was obtained as a microcrystalline powder, with a new set of hydrogen bonds. In the following step, initiated by heating, compound A-B+ was transformed into solid C by a condensation reaction. Aromatic diimides are normally obtained by classical organic synthesis using at least two solvent-based processes, and potentially more if a purification step is required. For example, compound 2b (bis(pyridyl)phenyldiimide), used recently in electron transfer reactions,6 was first synthesized in 1971 by dissolving the starting materials in dry N-methylpyrrolidone (glacial acetic acid was used for other aromatic diimides), followed by heating to 150–180 °C for 3 h, and separation and purification steps.7 Today, this general preparative method is * To whom correspondence should be addressed. E-mail: antonia.neels@ unine.ch.

Scheme 1. Schematic Representation of the “One Pot-Two Step” Process

used for the synthesis of a variety of diimide derivatives. Here, we report on how such aromatic diimides can be formed simply, and how their three-dimensional structure can be elucidated directly by X-ray powder diffraction analysis. The compounds, bis(pyrazyl)phenyldiimide (1b), bis(pyridyl)phenyldiimide (2b), and bis(2-chloro-pyridyl)phenyldiimide (3b), were obtained in a rapid and economical manner with quantitative yield. Experimental Section Thermogravimetric analyses were carried out using a METTLER 4000 thermogravimetric module and closed aluminum oxide crucibles (heating rate: 2°/min). In the thermogravimetric analyses, from room temperature to about 80 °C, the surface humidity of the samples is eliminated. The following weight-loss step corresponds to the elimination of two water molecules, initially crystallized with H4-BCTA. The last step corresponds to the elimination of four water molecules, which is the result of the condensation reaction. The values found for the last step are slightly higher than the theoretical values probably due to the sublimation of a small excess of amine in the reaction mixture. All the microwave-assisted reactions described were performed in open glass vessels with a commercial Microwave system at a frequency of 2450 MHz (130–800 W). Infrared spectra were recorded with a Perkin-Elmer Spectrum One spectrometer in transmission mode using KBr pellets. The elemental microanalyses were performed by the Microanalysis service of the Laboratory of Pharmaceutical and Organic Propedeutical Chemistry at the University of Geneva (Switzerland). EI mass spectra were performed on a Finnegan Polaris Q mass spectrometer.

General Synthetic Procedures Compounds 1a, 2a, and 3a were synthesized by a) exposing the respective starting materials [H4-BCTA:R-NH2 ) 1:2; R ) pyrazine (1a), pyridine (2a), o-chloro-pyridine (3a)] to microwave (MW)

10.1021/cg070058q CCC: $40.75  2008 American Chemical Society Published on Web 03/04/2008

1148 Crystal Growth & Design, Vol. 8, No. 4, 2008

Neels et al.

Table 1. Crystallographic Data for Compounds 1a, 2a, and 3a

formula M cryst syst space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Dcalcd (g cm-3) Z µCu (mm-1) pattern range (° 2θ) step size (deg) step scan time (min) no. of contributing reflns no. of struct. params no. of profile params no. of restraints Rwpa Rpb RFc a

1a

2a

3a

[(C10H4O8)(C4H6N3)2] 444.36 monoclinic P21/c 11.2777(6) 12.8578(5) 6.4718(2) 90 94.697(4) 90 935.30(5) 1.578 2 1.09 4–80 0.01 144 1276 79 18 79 0.068 0.052 0.048

[(C10H4O8)(C5H7N2)2] 442.38 triclinic P1j 11.3987(2) 11.8643(2) 3.8022(1) 96.365(1) 95.906(1) 108.898(1) 478.19(1) 1.536 1 1.03 4–80 0.01 208 1148 73 18 84 0.052 0.038 0.064

[(C10H4O8)(C5H6N2Cl)2] 511.28 monoclinic P21/n 22.384(1) 3.9587(2) 11.6243(7) 90 98.094(5) 90 1019.78(9) 1.665 2 3.42 6–80 0.01 208 1238 96 18 90 0.078 0.056 0.050

Rwp ) [Σw(Io - Ic)2/ΣwIo2]1/2. b Rp ) Σ|Io - Ic|/ΣIc. c RF ) Σ|Fo| - |Fc|/Σ|Fo|.

Scheme 2. Two Step Solid-State Reactions

irradiation at 600W for 60 min or b) heating to 180 °C for 1a, 120 °C for 2a, and 180 °C for 3a in a thermogravimetric module. Compounds 1b, 2b, and 3b were synthesized from a mixture of the starting materials [H4-BCTA:R-NH2 ) 1:2; R ) pyrazine (1b), pyridine (2b), o-chloropyridine (3b)] by heating at 260 °C, 190 and 220 °C, respectively, using a thermogravimetric module. The starting materials were completely converted to the respective products in all the cases. No side products were obtained. Compound 1a: Elemental anal. (%) Calcd for C18H16N6O8: C, 48.61; H, 3.60; N, 18.90. Found: C, 48.42; H, 3.26; N, 18.21. IR: ν˜ 1700.97(m), 1660.79(br, s), 1614.05(m), 1579.13(s) cm-1. TG (weight loss, %): 7.2 (-2H2O, theor. 7.5). Compound 2a: Elemental anal. (%) Calcd for C20H18N4O8: C, 54.30; H, 4.07; N, 12.67. Found: C, 54.15; H, 3.87; N, 12.56. IR: ν˜ 1698.23(m), 1654.61(br, s), 1616.15(m), 1591.29(m), 1567.20(m) cm-1. TG (weight loss, %): 7.8 (-2H2O, theor. 7.5). Compound 3a: Elemental anal. (%) Calcd for C20H16Cl2N4O8: C, 46.97; H, 3.16; N, 10.96. Found: C, 46.70; H, 3.11; N, 9.75. IR: ν˜ 1712.02(m), 1645.21(br, s), 1607.69(m), 1581.12(s), 1538.89(s) cm-1. TG (weight loss, %): 6.0 (-2H2O, theor. 6.6). Compound 1b: Elemental anal. (%) Calcd for C18H8N6O4: C, 58.06; H, 2.15; N, 22.58. Found: C, 57.04; H, 2.10; N, 21.08. IR: ν˜ 1784.17(m), 1737.93(br, s), 1456.16(w), 1416.21(s), 720.96(s) cm-1. EI-MS: m/z 372.78 [1b]+. TG (weight loss, %): 16.7 (-4H2O, theor. 15.0). Compound 2b: Elemental anal. (%) Calcd for C20H10N4O4: C, 64.87; H, 2.72; N, 15.13. Found: C, 64.48; H, 2.90; N, 15.04. IR: ν˜ 1786.77(w), 1725.31(br, s), 1452.37(w), 1399.86(m), 719.77(s) cm-1. EI-MS: m/z 370.13 [2b]+. TG (weight loss, %): 16.5 (-4H2O, theor. 15.0). Compound 3b: Elemental anal. (%) Calcd for C20H8Cl2N4O4: C, 54.68; H, 1.82; N, 12.76. Found: C, 54.67; H, 2.04; N, 12.55. IR: ν˜

1779.80(m), 1733.20(br, s), 1386.02(s), 724.94(m) cm-1. EI-MS: m/z 437.74 [3b]+. TG (weight loss, %): 14.8 (-4H2O, theor. 13.2). X-Ray Powder Diffraction. The powder samples 1a, 2a, 3a, 1b, 2b, and 3b were inserted in glass capillaries of 0.5 mm diameter. X-ray powder data were collected in the Debye–Scherrer mode at room temperature on a computer controlled STOE-STADIP focusing powder diffractometer8 equipped with a curved Ge(111) monochromator (λ ) 1.54051Å). A STOE linear position sensitive detector was used. The compounds were measured in the range of 4° e 2θ e 80° using a step width of 0.01°. The indexing procedure was performed using ITO9a in WinXPow.9b The structure solution was carried out using the program DASH10a introducing structural models.10b The position of the molecule obtained, in the given symmetry and unit cell, was used for Rietveld refinement in GSAS/EXPGUI.11 After the initial refinement of the scale and unit cell constants, the atomic positions were refined using soft constraints defining the geometry of the molecule within some allowable errors.12 Subsequent Rietveld refinement was carried out gradually relaxing the bond restraints. The nonhydrogen atoms were refined isotropically applying an overall temperature factor for the C, N, O atoms. The positions and temperature factors of the H-atoms were fixed. In the final cycles of refinement, the shifts in all the parameters were less than their standard uncertainties (e.s.d’s). Further details of the data collection and refinement are shown in Table 1. Molecular drawings were obtained using PLATON.13

Results and Discussion Synthesis of Compounds 1a, 2a, 3a and 1b, 2b, and 3b. Two different types of thermally activated solid-state reactions were

Solid-State Synthesis of New Diimid Compounds

Figure 1. Thermogravimetry showing the principal weight losses in the two-step synthesis of compounds 1b, 2b, and 3b. The process can be accelerated by heating. The organic salts, [(H2-BCTA)(HR-NH2)2], were formed at 120 °C (1a) and at 180 °C (2a, 3a). No melting was observed during the formation of 1a, 2a, and 3a [mp (H4-BCTA · 2H2O) ) 281–284 °C; mp (pyrazine-2ylamine) ) 118–120 °C; mp (pyridine4ylamine) ) 155–158 °C; mp (2-chloro-pyridin-4ylamine) ) 90–94 °C].

Crystal Growth & Design, Vol. 8, No. 4, 2008 1149

Figure 3. Crystal packing diagram of 1a (hydrogen bonds shown as dotted lines) with the hydrogen bonding pattern: N1 ) C33(10)C(5)R21 (4)R12(6)R32(13) (chains are visualized by ribbons, I, II, III ) rings).

Figure 4. Molecular structure of compound 2a, showing the atomic numbering scheme. The Rietveld refinement plots are also shown, and include the difference curve between the calculated (-) and measured (+) X-ray powder diffractograms.


carried out sequentially, in a one-pot synthesis (Scheme 2). The first step (a) involves an intersolid reaction between the acid, 1,2,4,5-benzenetetracarboxylic acid (H4-BCTA), and the various bases [R-NH2 ) pyrazin-2-ylamine (1), pyridin-4-ylamine (2), and 2-chloro-pyridin-4-ylamine (3)]. Hydrogen transport from the neutral H4-BCTA molecule to the R-NH2 molecule (acid/ base reaction) results in the formation of the intermediate compounds. In these organic salts, the ions are connected by hydrogen bonds to form a 2D network. The second step (b), involves an intrasolid condensation reaction resulting in the formation of the new diimide compounds, 1b, 2b, and 3b. Thermogravimetric Analysis. The solid-state reactions were followed by thermogravimetry (Figure 1). The starting materials were mixed and heated slowly to 300 °C. The thermogravimetric curve shows an initial small weight loss, between 50–75 °C, due to the elimination of surface humidity of the samples. There then follows two further weight losses for each reaction mixture. The first is due to the loss of the water of crystallization of H4-BCTA · 2H2O and the formation of the intermediate compound (1a, 2a, and 3a). The latter are formed after grinding both starting materials in the correct ratio followed by heating.

XRPD analyses showed that the process occurs also at room temperature but the transformation is much slower; the XRPD pattern showed initially a mixture of the two starting materials. Description of Structures of Compounds 1a, 2a, and 3a. The three-dimensional structures of these intermediate compounds were derived directly by XRPD of the powders formed, without any purification or recrystallization steps. The quality of all of the powder diffractograms allowed structure solution and Rietveld refinement (Table 1). The molecular structures of compounds 1a, 2a, and 3a, including the numbering scheme and the final Rietveld plots, are shown in Figures 4, 6, and 8, respectively. In the starting material, H4-BCTA · 2H2O, the carboxylate groups are twisted with respect to the plane of the benzene ring by ca. 19.2 and 72.5°.14 However, in compounds 1a, 2a, and 3a, the carboxylate groups in the [H2-BCTA]2- anions are coplanar with respect to the benzene ring, This is due to the formation of intramolecular hydrogen bonds involving adjacent carboxylate groups. The CdO bond distances in the [H2BCTA]2- anion are longer than those in the neutral acid H4BCTA, probably due the electronic delocalization in the conjugated bonds (Table 3). As a result of the protonation of the heteroaromatic amines and the formation of the [HR-NH2]+ cations, the aromatic C-N bonds are longer and the C-N-C angle larger than those observed in the neutral amines. The ratio of 1:2 for [H2-BCTA]2–: [HR-NH2]+ provides the neutrality of the compound. An extended hydrogen bonding network is


Figure 5. Crystal packing diagram of 2a (hydrogen bonds shown by dotted lines) with the hydrogen bonding pattern: N1 ) C33(12)R21 (4)R44(12)R44(28)R46(20) (chains are visualized by a ribbon; I, II, III, IV ) rings).

Neels et al.

Figure 8. Molecular structure of compound 1b, showing the atomic numbering scheme. The Rietveld refinement plots are also shown, and include the difference curve between the calculated (-) and measured (+) X-ray powder diffractograms. Table 2. Hydrogen Bonds for Compounds 1a, 2a, and 3a 1a Aa

D N1 N1 N1 N2 N2

i

N3 O1ii O3iii O3iii O4iii

2a

D · · · A (Å) 2.916(7) 2.849(9) 3.288(7) 3.038(7) 2.722(8)

Å

Aa iv

N1 O4 N2 O1v N2 O2vi

3a

D · · · A (Å)

D

Aa

D · · · A (Å)

2.758(5) 2.819(4) 3.115(4)

N1 N1 N2 N2 N2

O1 O2 O3vii O4vii O4vii

2.790(11) 3.320(11) 3.070(12) 3.209(11) 3.173(11)

Symmetry operations: (i) -x, 0.5 + y, 1.5 - z; (ii) -x, 1 - y, 1 - z; (iii) 1 - x, -0.5 + y, 1.5 - z; (iv) 1 - x, y, 1 + z; (v) x, y, -1 + z; (vi) 1 - x, -y, -z; (vii) x, 1 + y, z. a


Figure 7. Crystal packing diagram of 3a (hydrogen bonds shown as dotted lines) with the hydrogen bonding pattern: N1 ) C45(24)C33(12)R24(8)R21 (4)R44(28)R46(20) (chains are visualized by ribbons; I, II, III, IV ) rings).

observed (Table 2), that can be described by the graph set descriptors Gad(n) (where G is C for a chain, R for a ring, S for the intramolecular hydrogen pattern, and n ) the number of atoms in the pattern. The number of hydrogen bonding donors

is given by the subscript d, and the number of hydrogen bonding acceptors by the superscript a).15,16 The intramolecular hydrogen bonding motif present in all three intermediate compounds, 1a-3a, is S. For 1a, the asymmetric unit consists of a monoprotonated amino-pyrazinium cation and half a centrosymmetric [H2BCTA]2- anion (Figure 2). In the amino-pyrazine cation, atom N2 is protonated, whereas the aromatic N3 atom and the amino nitrogen atom N1 remain neutral. The aromatic C-N bond distances, involving the protonated N2 atom, are longer compared to those found in neutral pyrazine-2ylamine (Table 3).17 The C6-N2-C9 bond angle is larger in 1a than in the starting material. Similar behavior has been observed for other protonated pyrazine derivatives.18 The crystal packing diagram for 1a (Figure 3) shows that the [H2-BCTA]2- and amino-pyrazinium ions are connected Via hydrogen bonds (Table 2) generating a 2D structure. Classical hydrogen bonds generate a hydrogen bonding pattern containing five motifs, N1 ) C33(10)C(5)R21(4)R12(6)R32(13) , including 2 chains and 3 rings. The NH2 function of the amino-pyrazinium cation links the planar [H2-BCTA]2- ions resulting in a chain motive. Perpendicular to this chain a second hydrogen bonded chain can be seen, involving only the amino-pyrazine cations, via their NH donor and N acceptor functions. The best leastsquares planes through the [H2-BCTA]2- and amino-pyrazinium ions, are inclined to one another by 10.0(2)°. As a consequence of the change in the CdO and CdN bond distances, the IR absorption bands shift to lower frequencies compared to those found for the neutral starting materials, H4BCTA and pyrazine-2-ylamine (Table 3). For 2a, the asymmetric unit contains one protonated aminopyridinium cation in a general position, and half a centrosym-

Solid-State Synthesis of New Diimid Compounds

Crystal Growth & Design, Vol. 8, No. 4, 2008 1151

Table 3. Selected Bond Distances, Bond Angles, and Vibrational Absorption Bands for the Starting Materials and the Organic Salts 1a, 2a, and 3a compd H4-BCTA

pyrazine-2-ylamine10 (o-N-atom) 1a

pyridine-4-ylamine12 2a

Cl-pyridine-4-ylamine derivative14 3a

νC)O/νC)N (cm-1)

CdO/CdN (Å)

7

C4-O1 C4-O2 C5-O3 C5-O4 C6-N2 C9-N2 1.352 1.338 C4-O1 C4-O2 C5-O3 C5-O4 C9-N1 C8-N1 1.340 1.338 C4-O1 C4-O2 C5-O3 C5-O4 C9-N1 C8-N1

1.212 1.219 1.337 1.330 1.296(3) 1.294(3) 1.292(3) 1.296(3) 1.356(3) 1.346(3)

C-N-C (deg)

1700 (br,s) 1648 (br,s)

116.5

1661 (br, s) 1614 (m)

C6-N2-C9

1648 (s) 1.255(5) 1.296(5) 1.301(4) 1.258(5) 1.362(3) 1.352(3)

115.0

1655 (s) 1616 (m)

C8-N1-C9

1657 (s) 1.23(1) 1.28(1) 1.28(1) 1.24(1) 1.339(9) 1.358(9)

metric [H2-BCTA]2- anion (Figure 4). In the amino-pyridinium cation, the aromatic C-N bond distances involving atom N1, are longer compared to those observed in neutral pyridine4ylamine (Table 3),19 and the C8-N1-C9 angle is larger compared to that observed in the neutral amino pyridine. This effect has also been observed previously for other pyridine/ pyridinium systems.20 In the crystal structure of 2a, hydrogen bonded twodimensional layers are present, that can be described by a centrosymmetric graph set, N1 ) C33(12)R21(4)R44(12)R44(28)R46 (20) (Figure 5). One chain motif, containing alternating [H2BCTA]2- and amino-pyridinium ions, can be defined and involves NH and OH donors and O acceptor functions. Four ring motifs (I–IV) are present. In these two-dimensional hydrogen bonded sheets, the [H2BCTA]2- and amino-pyridinium ions are tilted with respect to one another by 19.6(1)°. As a result of the change in the C-N and C-O bond distances, the CdN and the CdO vibrational bands in the IR spectrum of 2a are shifted toward lower wavenumbers (Table 3). The range 1700–1400 cm-1 is dominated by the stretching and bending vibrational absorption bands of the pyridinium and benzene aromatic systems. For 3a, the asymmetric unit contains one protonated 4-amino2-chloro-pyridinium cation in a general position and half of a centrosymmetric [H2-BCTA]2- anion (Figure 6). As found for 2a, in the 4-amino-2-chloro-pyridinium cation the aromatic C-N bond distances, involving the protonated N1 atom, are longer compared to those found in the crystal structure of the neutral 2-chloro-pyridin-4ylamine derivative (Table 3). 21The C8-N1C9 bond angle is also found to be larger compared to that in the neutral amino pyridine. The variations in the bond distances are as pronounced as those found for the 4-amino-pyridinium cation (2a), probably due to the electronic influence of the chlorine atom in the pyridinium system. In the crystal structure of 3a, hydrogen-bonded twodimensional layers are present. The graph set contains six motif descriptors, N1 ) C45(24)C33(12)R24(8)R21(4)R44(28)R46(20) (Figure 7). The two chains involve NH and OH donors and O acceptor functions. Four ring motifs (I–IV) are also observed.

121.2(3)

121.4(2) 116.8

1645 (s) 1608 (m)

C8-N1-C9

122.0(6)

In the two-dimensional hydrogen-bonded sheetlike structure, the flat [H2-BCTA]2- and 4-amino-2-chloro-pyridinium ions are inclined to one another by 49.0(2)°. In accordance with the changes in the C-N and C-O bond distances, in the IR spectrum of 3a the CdN and the CdO vibrational absorption bands are shifted toward lower wavenumbers compared to those observed for the starting materials, as shown in Table 3. Description of Structures of Compounds 1b, 2b, and 3b. From the structural arrangements observed in compounds 1a, 2a and 3a, one can see that the subsequent condensation step of BCTA with the corresponding amine in the ratio 1:2 is perfectly prepared. In this second step, as followed by thermogravimetry, the weight losses at 190, 260, and 220° correspond to the simultaneous removal of four water molecules resulting in the formation of compounds 1b, 2b, and 3b, respectively (Scheme 1). Again, the three-dimensional structures were derived directly by XRPD of the crude products and did not require any purification or recrystallization steps. The quality of all of the powder diffractograms allowed structure solution and Rietveld refinement (Table 4). The molecular structures of compounds 1b, 2b, and 3b, including the numbering scheme and the final Rietveld plots, are illustrated in Figures 8, 10 and 12, respectively. Compound 1b crystallized in the orthorhrombic noncentrosymmetric space group Pca21. The pyrazine rings and the aromatic diimide system are twisted with respect to one another. The dihedral angle between ring (N3, N4, C11–C14) and the diimide system is 42.6(2)°, whereas that between ring (N5, N6, C15–C18) and the diimide system it is 87.1(1)° (Figure 8). As a consequence of the absence of any N-H or O-H functions in the molecule, the crystal packing of 1b is controlled by C-H · · · N hydrogen bonds [C14-H14 · · · N2i ) 3.341(4) Å, symmetry operation (i) ) –x, -y, 1/2 + z] and van der Waals interactions (Figure 9). Compound 2b possesses Ci symmetry and the molecular structure is illustrated in Figure 10. The pyridine ring and the aromatic diimide system are twisted with respect to one another by 57.9(2)°. The absence of hydrogen donor functions in 2b, such as N-H or O-H, excludes hydrogen bonding in the crystal packing.


Neels et al.

Table 4. Crystallographic Data for Compounds 1b, 2b, and 3b

formula M cryst syst space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Dcalcd (g cm-3) Z µCu (mm-1) pattern range (° 2θ) step size (deg) step scan time (min) no. of contributing reflns no. of struct. params no. of profile params no. of restraints Rwpa Rpb RFc

1b

2b

3b

[C18H8N6O4] 372.30 orthorhombic Pca21 9.6229(1) 17.8130(4) 9.2418(1) 90 90 90 1584.16(4) 1.561 4 0.98 6–80 0.01 126 670 116 18 124 0.063 0.048 0.080

[C20H10N4O4] 370.32 orthorhombic Cmca 34.586(2) 5.7132(1) 8.0155(1) 90 90 90 1583.82(8) 1.553 4 0.938 8–80 0.01 194 504 41 18 48 0.054 0.041 0.069

[C20H8N4O4Cl2] 439.22 monoclinic P21/c 7.8867(5) 7.5288(6) 14.3507(9) 90 93.163(7) 90 850.8(1) 1.714 2 3.806 8–80 0.01 130 1038 85 18 80 0.063 0.048 0.037

Figure 10. Molecular structure of compound 2b, showing the atomic numbering scheme. The Rietveld refinement plots are also shown, and include the difference curve between the calculated (-) and measured (+) X-ray powder diffractograms.

a Rwp ) [Σw(Io - Ic)2/ΣwIo2]1/2. b Rp ) Σ|Io - Ic|/ΣIc. c RF ) Σ|Fo| |Fc|/Σ|Fo|.

Figure 11. Crystal packing diagram of 2b viewed along the b axis (close contacts are shown by dotted lines).

Figure 9. Partial crystal packing diagram of 1b, viewed along the b axis.

Close O · · · O and O · · · N intermolecular contacts (

Solid-State Synthesis of New Diimide Compounds - American

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