research communications
Dimethyl and diethyl
of 5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylic acid: a comparisonaInstitute of Chemistry, University of Neuchâtel, Av. de Bellevaux 51, CH-2000 Neuchâtel, Switzerland, and bInsitute of Physics, University of Neuchâtel, rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland
*Correspondence e-mail: helen.stoeckli-evans@unine.ch
In dimethyl 5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate, C18H14N4O4, (I), and diethyl 5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate, C20H18N4O4, (II), the dimethyl and diethyl of 5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylic acid, the orientation of the two pyridine rings differ. In (I), pyridine ring B is inclined to pyrazine ring A by 44.8 (2)° and the pyridine and pyrazine N atoms are trans to one another, while pyridine ring C is inclined to the pyrazine ring by 50.3 (2)°, with the pyridine and pyrazine N atoms cis to one another. In compound (II), the diethyl ester, which possesses twofold rotation symmetry, the pyridine ring is inclined to the pyrazine ring by 40.7 (1)°, with the pyridine and pyrazine N atoms trans to one another. In the crystal of (I), molecules are linked by C—H⋯N hydrogen bonds, forming chains along [001]. The chains are linked by C—H⋯π interactions, forming a three-dimensional structure. In the crystal of (II), molecules are linked via C—H⋯O hydrogen bonds, forming a three-dimensional framework. There are C—H⋯π interactions present within the framework.
1. Chemical context
5,6-Bis(pyridin-2-yl)pyrazine-2,3-dicarboxylic acid (L1H2) was synthesized to study its coordination behaviour with first row transitions metals (Alfonso, 1999). It exists as a zwitterion, with the adjacent pyridine and pyridinium rings almost coplanar due to the presence of an intramolecular N—H⋯N hydrogen bond. The crystal structures of the zwitterion and different charged forms of L1H2, viz. the HCl, HClO4 and HPF6 salts, and details of the hydrogen bonding have been reported (Alfonso et al., 2001).
Metal-catalysed hydrolysis of amino acid ). It has been shown previously that the reaction of copper(II) salts with the dimethyl of pyrazine-2,3-dicarboxylic acid (Neels et al., 1997) and 2,5-dimethylpyrazine-3,6-dicarboxylic acid (Wang & Stoeckli-Evans, 1998) resulted in the partial hydrolysis of the ligand and the formation of a two-dimensional network in the first case and a mononuclear complex in the second. Hence, metal-ion-promoted ester hydrolysis leads to the formation of new ligands and may serve as a general route to prepare new coordination compounds. The title compounds, (I) and (II), were synthesized to study the hydrolysis of these with first row transition metals (Alfonso, 1999), and we report herein on their syntheses and crystal structures.
is a well documented phenomenon (Dugas, 19892. Structural commentary
As seen in compound (I), Fig. 1, the dimethyl ester of L1H2, pyridine ring B (N4/C10–C14) is inclined to the pyrazine ring (A; N1/N2/C1–C4) by 44.8 (2)° and the pyridine and pyrazine N atoms, N1 and N4, are trans to one another. Pyridine ring C (N3/C5–C9) is inclined to pyrazine ring A by 50.3 (2)°. However, here the pyridine and pyrazine N atoms, N2 and N3, are cis to one another. The two pyridine rings, B and C, are inclined to one another by 60.2 (2)°. The acetate groups, O1/O2/C15/C17 and O3/O4/C16/C18, are almost planar with r.m.s. deviations of 0.027 and 0.007 Å, respectively. They are inclined to the pyrazine ring by 60.3 (3) and 49.8 (3)°, respectively, and to one another by 42.4 (3)°.
Compound (II), the diethyl ester of L1H2, possesses twofold rotation symmetry, with the twofold rotation axis bisecting the Car—Ciar bonds [ar = aromatic; symmetry code (i): −x + 2, −y + , z], as shown in Fig. 2. The pyridine N atoms, N2 and N2i, face one another with an N2⋯N2i separation of 3.043 (3) Å. The two pyridine rings are inclined to one another by 55.1 (1)° and to the pyrazine ring mean plane by 40.7 (1)°, with the pyrazine and pyridine N atoms, N1 and N2, trans to one another. The acetate group, O1/O2/C8/C9 [maximum deviation of 0.012 (3) Å for atom C8] is inclined to the pyrazine ring mean plane by 38.9 (1)°, and by 47.6 (2)° to the acetate group related by the twofold rotation axis. The oxygen atoms, O2 and O2i, are separated by only 2.840 (3) Å. The pyrazine ring in (II) has a slight twist-boat conformation (r.m.s. deviation = 0.046 Å) with the N1/C1/C2 and N1i/C1i/C2i planes inclined to one another by 3.9 (3)°.
As noted above the differences in the structures of the two compounds lies essentially in the orientation of the pyridine rings with respect to the pyrazine ring (cf Figs. 1 and 2). It is possible that the slight distortion of the planarity of the pyrazine ring in (II), mentioned above, is related to the short N2⋯N2i contact of 3.043 (3) Å of the adjacent pyridine rings and to the even shorter O2⋯O2i contact of 2.840 (3) Å of the adjacent acetate groups.
3. Supramolecular features
In the crystal of (I), molecules are linked by C—H⋯N hydrogen bonds, forming chains along [001]; see Table 1 and Fig. 3. The chains are linked via C—H⋯π interactions (Table 1), forming a three-dimensional structure.
In the crystal of (II), molecules are linked via C—H⋯O hydrogen bonds, forming a three-dimensional framework; see Table 2 and Fig. 4. Within the framework there are a number of C—H⋯π interactions present (Table 2).
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4. Database survey
Besides the structures of the zwitterion and different charged forms of L1H2, viz. the HCl, HClO4 and HPF6 salts (Alfonso et al., 2001), the crystal structures of two copper(II) complexes of L1H2 have been reported, viz: catena-[[[μ3-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate]triaquadibromodicopper(II)] methanol solvate trihydrate] and catena-[[[μ4-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate)diaquadibromodicopper(II) monohydrate] (Neels et al., 2003).
The structure of the isoelectronic compound 3,6-bis(pyridin-2-yl)pyrazine-2,5-dicarboxylic acid (L2H2), Fig. 5, has also been reported (Wang & Stoeckli-Evans, 2012a). It too exists as a zwitterion and the structures of its dihydrochloride salt and the dimethyl sulfonate disolvate have also been reported (Wang & Stoeckli-Evans, 2012a). The crystal structures of the dimethyl (III) and diethyl (IV) of L2H2 have been deposited as private communications (Wang & Stoeckli-Evans, 2012b,c) with the Cambridge Structural Database (CSD; Groom & Allen, 2014). Both compounds crystallize in the triclinic P and possess inversion symmetry. The pyridine rings lie almost in the plane of the pyrazine ring and the N atoms are trans with respect to each other and to the nearest pyrazine N atom (as illustrated in Fig. 5). The ester groups are planar and in both compounds lie almost normal to the pyrazine ring. In the crystals of both compounds, inversion-related molecules are linked via pairs of C—H⋯O hydrogen bonds, enclosing R22(10) ring motifs, forming chains propagating along [10].
5. Synthesis and crystallization
The synthesis of 5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylic acid (L1H2) has been reported (Alfonso et al., 2001). The dimethyl and diethyl compounds (I) and (II), respectively, were obtained by the usual esterification procedure in acidic medium from the diacid and an excess of the corresponding alcohol.
Synthesis of compound (I): dimethyl-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate L1H2
(1.00 g, 3.11 mmol) was heated under reflux in freshly distilled MeOH (40ml) containing H2SO4 conc. (98%, 1 ml) during 16 h. After stopping the reaction, the temperature of the solution was allowed to cool to room temperature and then poured into an aqueous solution of NaOAc (6 g in 150 ml deionized water). The resulting solution was stirred in an ice bath containing NaCl to afford a white solid which was removed by filtration, washed with cold water and dried under vacuum. Single crystals suitable for X-ray analysis were obtained by the slow diffusion technique from CH2Cl2 and MeOH (yield: 0.77g, 65%; m.p. 410.2–411.7 K). Selected IR bands (KBr pellet, cm−1): ν = 1743(s), 1729(vs), 1339(s), 1302(s), 1283(vs), 1164(s), 1089(vs). 1H NMR (CDCl3, 400 MHz, p.p.m.): δ = 8.34(dt, 2H, J = 4.1Hz, J = 1.0 Hz, pyH), 7.99(dt, 2H, J = 7.7 Hz, J = 1.0 Hz, pyH), 7.82(td, 2H, J = 7.7 Hz, J = 1.0 Hz, pyH), 7.26(td, 2H, J = 7.7 Hz, J = 1.0 Hz, pyH), 4.04(s, 6H, CH3). 13C NMR (CDCl3, 50 MHz, p.p.m.): δ = 165.53, 155.98, 153.35, 149.26, 142.92, 137.64, 125.41, 124.49, 54.11. DCI–MS m/z: 351(MH+), 318, 279, 255, 208. Analysis for C18H14N4O4 (350.33), calculated C 61.70, H 4.04, N 15.99%, found C 61.4, H 3.91, N 15.65%.
Synthesis of compound (II): diethyl-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate
This compound was prepared by the same method as for (I). L1H2 in freshly distilled EtOH containing catalytic amounts of H2SO4 conc. gave compound (II) as a white solid. Slow evaporation of an ethanolic solution afforded colourless crystals suitable for X-ray analysis (yield: 0.70g, 62%; m.p. 390.5–391.3 K). Selected IR bands (KBr pellet, cm−1): ν = 3055(w), 1737(s), 1723(vs), 1368(s), 1301(s), 1276(vs), 1276(vs), 1161(s), 1086(vs). 1H NMR (CDCl3, 400 MHz, p.p.m.): δ = 8.33(d, 2H, J = 4 Hz, pyH), 8.01(d, 2H, J = 7.7 Hz, pyH), 7.81(t, 2H, J = 7.7 Hz, pyH), 7.24(t, 2H, J = 4.4 Hz, pyH), 4.52(m, 4H, J = 7 Hz, CH2), 1.45(t, 6H, J = 7.4 Hz, CH3). EI–MS m/z: 378 (34), 349 (9), 232 (95), 206 (66), 179 (25), 152 (11), 129 (9), 78(base), 46 (38). Analysis for C20H18N4O4 (378.38), calculated C 63.49, H 4.79, N 14.81%, found C 63.49, H 4.61, N 14.77%.
6. Refinement
Crystal data, data collection and structure . For both compounds, the C-bound H-atoms were included in calculated positions and treated as riding atoms: C—H = 0.93–0.98 Å with Uiso(H) = 1.5Ueq(C-methyl) and 1.2Ueq(C) for other H atoms. For compound (I), the (Parsons et al., 2013) is = −0.2 (10), but it has no physical meaning here.
details are summarized in Table 3
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Supporting information
10.1107/S2056989016001080/gk2653sup1.cif
contains datablocks I, II, Global. DOI:Structure factors: contains datablock I. DOI: 10.1107/S2056989016001080/gk2653Isup2.hkl
Structure factors: contains datablock II. DOI: 10.1107/S2056989016001080/gk2653IIsup3.hkl
Supporting information file. DOI: 10.1107/S2056989016001080/gk2653Isup4.cml
Supporting information file. DOI: 10.1107/S2056989016001080/gk2653IIsup5.cml
5,6-Bis(pyridin-2-yl)pyrazine-2,3-dicarboxylic acid (L1H2) was synthesized to study its coordination behaviour with first row transitions metals (Alfonso, 1999). It exists as a zwitterion, with the adjacent pyridine and pyridinium rings almost coplanar due to the presence of an intramolecular N—H···N hydrogen bond. The crystal structures of the zwitterion and different charged forms of L1H2, viz. the HCl, HClO4 and HPF6 salts, and details of the hydrogen bonding have been reported (Alfonso et al., 2001).
Metal-catalysed hydrolysis of amino acid
is a well documented phenomenon (Dugas, 1989). It has been shown previously that the reaction of copper(II) salts with the dimethyl of pyrazine-2,3-dicarboxylic acid (Neels et al., 1997) and 2,5-dimethylpyrazine-3,6-dicarboxylic acid (Wang & Stoeckli-Evans, 1998) resulted in the partial hydrolysis of the ligand and the formation of a two-dimensional network in the first case and a mononuclear complex in the second. Hence, metal-ion-promoted ester hydrolysis leads to the formation of new ligands and becomes an extremely interesting manner to prepare new coordination compounds. The title compounds, (I) and (II), were synthesized to study the hydrolysis of these with first row transition metals (Alfonso, 1999), and we report herein on their syntheses and crystal structures.As seen in compound (I), Fig.1, the dimethyl ester of L1H2, pyridine ring B (N4/C10–C14) is inclined to the pyrazine ring (A; N1/N2/C1–C4) by 44.8 (2)° and the pyridine and pyrazine N atoms, N1 and N4, are trans to one another. Pyridine ring C (N3/C5–C9) is inclined to pyrazine ring A by 50.3 (2)°. However, here the pyridine and pyrazine N atoms, N2 and N4, are cis to one another. The two pyridine rings, B and C, are inclined to one another by 60.2 (2)° and to the planar pyrazine ring A (r.m.s. deviation 0.032 Å) by 44.8 (2) and 50.3 (2)°, respectively. The acetate groups, O1/O2/C15/C17 and O3/O4/C16/C18, are planar with r.m.s. deviations of 0.027 and 0.007 Å, respectively. They are inclined to the pyrazine ring by 60.3 (3) and 49.8 (3)°, respectively, and to one another by 42.4 (3)°.
Compound (II), the diethyl ester of L1H2, possesses twofold rotation symmetry, with the twofold rotation axis bisecting the Car—Ciar bonds [ar = aromatic; symmetry code (i): -x + 2, -y + 3/2, z], as shown in Fig. 2. The pyridine N atoms, N2 and N2i, face one another with an N2···N2i separation of 3.043 (3) Å. The two pyridine rings are inclined to one another by 55.1 (1)° and to the pyrazine ring mean plane by 40.7 (1)°, with the pyrazine and pyridine N atoms, N1 and N2, trans to one another. The acetate group, O1/O2/C8/C9 [maximum deviation of 0.012 (3) Å for atom C8] is inclined to the pyrazine ring mean plane by 38.9 (1)°, and by 47.6 (2)° to the acetate group related by the twofold rotation axis. The oxygen atoms, O2 and O2i, are separated by only 2.840 (3) Å. The pyrazine ring in (II) has a slight twist-boat conformation (r.m.s. deviation = 0.046 Å) with the N1/C1/C2 and N1i/C1i/C2i planes inclined to one another by 3.9 (3)°.
As noted above the differences in the structures of the two compounds lies essentially in the orientation of the pyridine rings with respect to the pyrazine ring (cf Figs. 1 and 2). It is possible that the slight distortion of the planarity of the pyrazine ring in (II), mentioned above, is related to the short N2···N2i contact of 3.043 (3) Å of the adjacent pyridine rings and to the even shorter O2···O2i contact of 2.840 (3) Å of the adjacent acetate groups.
In the crystal of (I), molecules are linked by C—H···N hydrogen bonds, forming chains along [001]; see Table 1 and Fig. 3. The chains are linked via C—H···π interactions (Table 1), forming a three-dimensional structure.
In the crystal of (II), molecules are linked via C—H···O hydrogen bonds, forming a three-dimensional framework; see Table 2 and Fig. 4. Within the framework there are a number of C—H···π interactions present (Table 2).
\ Besides the structures of the zwitterion and different charged forms of L1H2, viz. the HCl, HClO4 and HPF6 salts (Alfonso et al., 2001), the crystal structures of two copper(II) complexes of L1H2 have been reported, viz: catena-[[[µ3-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate]\ triaquadibromodicopper(II)] methanol solvate trihydrate] and catena-[[[µ4-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate)\ diaquadibromodicopper(II) monohydrate] (Neels et al., 2003).
The structure of the isoelectronic compound 3,6-bis(pyridin-2-yl)pyrazine-2,5-dicarboxylic acid (L2H2), Fig. 5, has also been reported (Wang & Stoeckli-Evans, 2012a). It too exists as a zwitterion and the structures of its dihydrochloride salt and the dimethyl sulfonate disolvate have also been reported (Wang & Stoeckli-Evans, 2012a). The crystal structures of the dimethyl (III) and diethyl (IV) 1 and possess inversion symmetry. The pyridine rings lie almost in the plane of the pyrazine ring and the N atoms are trans with respect to each other and to the nearest pyrazine N atom (as illustrated in Fig. 5). The ester groups are planar and in both compounds lie almost normal to the pyrazine ring. In the crystals of both compounds, inversion-related molecules are linked via pairs of C—H···O hydrogen bonds, enclosing R22(10) ring motifs, forming chains propagating along [101].
of L2H2 have been deposited as private communications (Wang & Stoeckli-Evans, 2012b,c) with the Cambridge Structural Database (CSD; Groom & Allen, 2014). Both compounds crystallize in the triclinic PThe synthesis of 5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylic acid (L1H2) has been reported (Alfonso et al., 2001). The dimethyl and diethyl
compounds (I) and (II), respectively, were obtained by the usual esterification procedure in acidic medium from the diacid and an excess of the corresponding alcohol.Synthesis of compound (I): dimethyl-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate L1H2 (1.00 g, 3.11 mmol) was heated under reflux in freshly distilled MeOH (40ml) containing H2SO4 conc. (98%, 1 ml) during 16 h. After stopping the reaction, the temperature of the solution was allowed to cool to room temperature and then poured into an aqueous solution of NaOAc (6 g in 150 ml deionized water). The resulting solution was stirred in an ice bath containing NaCl to afford a white solid which was removed by filtration, washed with cold water and dried under vacuum. Single crystals suitable for X-ray analysis were obtained by the slow diffusion technique from CH2Cl2 and MeOH (yield: 0.77g, 65%; m.p. 410.2–411.7 K). Selected IR bands (KBr pellet, cm-1): ν = 1743(s), 1729(vs), 1339(s), 1302(s), 1283(vs), 1164(s), 1089(vs). 1H NMR (CDCl3, 400 MHz, p.p.m.): δ = 8.34(dt, 2H, J = 4.1Hz, J = 1.0Hz, pyH), 7.99(dt, 2H, J = 7.7Hz, J = 1.0Hz, pyH), 7.82(td, 2H, J = 7.7Hz, J = 1.0Hz, pyH), 7.26(td, 2H, J = 7.7Hz, J = 1.0Hz, pyH), 4.04(s, 6H, CH3). 13C NMR (CDCl3, 50 MHz, p.p.m.): δ = 165.53, 155.98, 153.35, 149.26, 142.92, 137.64, 125.41, 124.49, 54.11. DCI–MS m/z: 351(MH+), 318, 279, 255, 208. Analysis for C18H14N4O4 (350.33), calculated C 61.70, H 4.04, N 15.99 %, found C 61.4, H 3.91, N 15.65 %.
Synthesis of compound (II): diethyl-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate
This compound was prepared by the same method as for (I). L1H2 in freshly distilled EtOH containing catalytic amounts of H2SO4 conc. gave compound (II) as a white solid. Slow evaporation of an ethanolic solution afforded colourless crystals suitable for X-ray analysis (yield: 0.70g, 62%; m.p. 390.5–391.3 K). Selected IR bands (KBr pellet, cm-1): ν = 3055(w), 1737(s), 1723(vs), 1368(s), 1301(s), 1276(vs), 1276(vs), 1161(s), 1086(vs). 1H NMR (CDCl3, 400 MHz, p.p.m.): δ = 8.33(d, 2H, J = 4Hz, pyH), 8.01(d, 2H, J = 7.7Hz, pyH), 7.81(t, 2H, J = 7.7Hz, pyH), 7.24(t, 2H, J = 4.4Hz, pyH), 4.52(m, 4H, J = 7Hz, CH2), 1.45(t, 6H, J = 7.4Hz, CH3). EI–MS m/z: 378 (34), 349 (9), 232 (95), 206 (66), 179 (25), 152 (11), 129 (9), 78(base), 46 (38). Analysis for C20H18N4O4 (378.38), calculated C 63.49, H 4.79, N 14.81 %, found C 63.49, H 4.61, N 14.77 %.
Crystal data, data collection and structure
details are summarized in Table 3. For both compounds, the C-bound H-atoms were included in calculated positions and treated as riding atoms: C—H = 0.93–0.98 Å with Uiso(H) = 1.5Ueq(C-methyl) and 1.2Ueq(C) for other H atoms. For compound (I), the (Parsons et al., 2013) is = -0.2 (10), but it has no physical meaning here.5,6-Bis(pyridin-2-yl)pyrazine-2,3-dicarboxylic acid (L1H2) was synthesized to study its coordination behaviour with first row transitions metals (Alfonso, 1999). It exists as a zwitterion, with the adjacent pyridine and pyridinium rings almost coplanar due to the presence of an intramolecular N—H···N hydrogen bond. The crystal structures of the zwitterion and different charged forms of L1H2, viz. the HCl, HClO4 and HPF6 salts, and details of the hydrogen bonding have been reported (Alfonso et al., 2001).
Metal-catalysed hydrolysis of amino acid
is a well documented phenomenon (Dugas, 1989). It has been shown previously that the reaction of copper(II) salts with the dimethyl of pyrazine-2,3-dicarboxylic acid (Neels et al., 1997) and 2,5-dimethylpyrazine-3,6-dicarboxylic acid (Wang & Stoeckli-Evans, 1998) resulted in the partial hydrolysis of the ligand and the formation of a two-dimensional network in the first case and a mononuclear complex in the second. Hence, metal-ion-promoted ester hydrolysis leads to the formation of new ligands and becomes an extremely interesting manner to prepare new coordination compounds. The title compounds, (I) and (II), were synthesized to study the hydrolysis of these with first row transition metals (Alfonso, 1999), and we report herein on their syntheses and crystal structures.As seen in compound (I), Fig.1, the dimethyl ester of L1H2, pyridine ring B (N4/C10–C14) is inclined to the pyrazine ring (A; N1/N2/C1–C4) by 44.8 (2)° and the pyridine and pyrazine N atoms, N1 and N4, are trans to one another. Pyridine ring C (N3/C5–C9) is inclined to pyrazine ring A by 50.3 (2)°. However, here the pyridine and pyrazine N atoms, N2 and N4, are cis to one another. The two pyridine rings, B and C, are inclined to one another by 60.2 (2)° and to the planar pyrazine ring A (r.m.s. deviation 0.032 Å) by 44.8 (2) and 50.3 (2)°, respectively. The acetate groups, O1/O2/C15/C17 and O3/O4/C16/C18, are planar with r.m.s. deviations of 0.027 and 0.007 Å, respectively. They are inclined to the pyrazine ring by 60.3 (3) and 49.8 (3)°, respectively, and to one another by 42.4 (3)°.
Compound (II), the diethyl ester of L1H2, possesses twofold rotation symmetry, with the twofold rotation axis bisecting the Car—Ciar bonds [ar = aromatic; symmetry code (i): -x + 2, -y + 3/2, z], as shown in Fig. 2. The pyridine N atoms, N2 and N2i, face one another with an N2···N2i separation of 3.043 (3) Å. The two pyridine rings are inclined to one another by 55.1 (1)° and to the pyrazine ring mean plane by 40.7 (1)°, with the pyrazine and pyridine N atoms, N1 and N2, trans to one another. The acetate group, O1/O2/C8/C9 [maximum deviation of 0.012 (3) Å for atom C8] is inclined to the pyrazine ring mean plane by 38.9 (1)°, and by 47.6 (2)° to the acetate group related by the twofold rotation axis. The oxygen atoms, O2 and O2i, are separated by only 2.840 (3) Å. The pyrazine ring in (II) has a slight twist-boat conformation (r.m.s. deviation = 0.046 Å) with the N1/C1/C2 and N1i/C1i/C2i planes inclined to one another by 3.9 (3)°.
As noted above the differences in the structures of the two compounds lies essentially in the orientation of the pyridine rings with respect to the pyrazine ring (cf Figs. 1 and 2). It is possible that the slight distortion of the planarity of the pyrazine ring in (II), mentioned above, is related to the short N2···N2i contact of 3.043 (3) Å of the adjacent pyridine rings and to the even shorter O2···O2i contact of 2.840 (3) Å of the adjacent acetate groups.
In the crystal of (I), molecules are linked by C—H···N hydrogen bonds, forming chains along [001]; see Table 1 and Fig. 3. The chains are linked via C—H···π interactions (Table 1), forming a three-dimensional structure.
In the crystal of (II), molecules are linked via C—H···O hydrogen bonds, forming a three-dimensional framework; see Table 2 and Fig. 4. Within the framework there are a number of C—H···π interactions present (Table 2).
\ Besides the structures of the zwitterion and different charged forms of L1H2, viz. the HCl, HClO4 and HPF6 salts (Alfonso et al., 2001), the crystal structures of two copper(II) complexes of L1H2 have been reported, viz: catena-[[[µ3-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate]\ triaquadibromodicopper(II)] methanol solvate trihydrate] and catena-[[[µ4-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate)\ diaquadibromodicopper(II) monohydrate] (Neels et al., 2003).
The structure of the isoelectronic compound 3,6-bis(pyridin-2-yl)pyrazine-2,5-dicarboxylic acid (L2H2), Fig. 5, has also been reported (Wang & Stoeckli-Evans, 2012a). It too exists as a zwitterion and the structures of its dihydrochloride salt and the dimethyl sulfonate disolvate have also been reported (Wang & Stoeckli-Evans, 2012a). The crystal structures of the dimethyl (III) and diethyl (IV) 1 and possess inversion symmetry. The pyridine rings lie almost in the plane of the pyrazine ring and the N atoms are trans with respect to each other and to the nearest pyrazine N atom (as illustrated in Fig. 5). The ester groups are planar and in both compounds lie almost normal to the pyrazine ring. In the crystals of both compounds, inversion-related molecules are linked via pairs of C—H···O hydrogen bonds, enclosing R22(10) ring motifs, forming chains propagating along [101].
of L2H2 have been deposited as private communications (Wang & Stoeckli-Evans, 2012b,c) with the Cambridge Structural Database (CSD; Groom & Allen, 2014). Both compounds crystallize in the triclinic PThe synthesis of 5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylic acid (L1H2) has been reported (Alfonso et al., 2001). The dimethyl and diethyl
compounds (I) and (II), respectively, were obtained by the usual esterification procedure in acidic medium from the diacid and an excess of the corresponding alcohol.Synthesis of compound (I): dimethyl-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate L1H2 (1.00 g, 3.11 mmol) was heated under reflux in freshly distilled MeOH (40ml) containing H2SO4 conc. (98%, 1 ml) during 16 h. After stopping the reaction, the temperature of the solution was allowed to cool to room temperature and then poured into an aqueous solution of NaOAc (6 g in 150 ml deionized water). The resulting solution was stirred in an ice bath containing NaCl to afford a white solid which was removed by filtration, washed with cold water and dried under vacuum. Single crystals suitable for X-ray analysis were obtained by the slow diffusion technique from CH2Cl2 and MeOH (yield: 0.77g, 65%; m.p. 410.2–411.7 K). Selected IR bands (KBr pellet, cm-1): ν = 1743(s), 1729(vs), 1339(s), 1302(s), 1283(vs), 1164(s), 1089(vs). 1H NMR (CDCl3, 400 MHz, p.p.m.): δ = 8.34(dt, 2H, J = 4.1Hz, J = 1.0Hz, pyH), 7.99(dt, 2H, J = 7.7Hz, J = 1.0Hz, pyH), 7.82(td, 2H, J = 7.7Hz, J = 1.0Hz, pyH), 7.26(td, 2H, J = 7.7Hz, J = 1.0Hz, pyH), 4.04(s, 6H, CH3). 13C NMR (CDCl3, 50 MHz, p.p.m.): δ = 165.53, 155.98, 153.35, 149.26, 142.92, 137.64, 125.41, 124.49, 54.11. DCI–MS m/z: 351(MH+), 318, 279, 255, 208. Analysis for C18H14N4O4 (350.33), calculated C 61.70, H 4.04, N 15.99 %, found C 61.4, H 3.91, N 15.65 %.
Synthesis of compound (II): diethyl-5,6-bis(pyridin-2-yl)pyrazine-2,3-dicarboxylate
This compound was prepared by the same method as for (I). L1H2 in freshly distilled EtOH containing catalytic amounts of H2SO4 conc. gave compound (II) as a white solid. Slow evaporation of an ethanolic solution afforded colourless crystals suitable for X-ray analysis (yield: 0.70g, 62%; m.p. 390.5–391.3 K). Selected IR bands (KBr pellet, cm-1): ν = 3055(w), 1737(s), 1723(vs), 1368(s), 1301(s), 1276(vs), 1276(vs), 1161(s), 1086(vs). 1H NMR (CDCl3, 400 MHz, p.p.m.): δ = 8.33(d, 2H, J = 4Hz, pyH), 8.01(d, 2H, J = 7.7Hz, pyH), 7.81(t, 2H, J = 7.7Hz, pyH), 7.24(t, 2H, J = 4.4Hz, pyH), 4.52(m, 4H, J = 7Hz, CH2), 1.45(t, 6H, J = 7.4Hz, CH3). EI–MS m/z: 378 (34), 349 (9), 232 (95), 206 (66), 179 (25), 152 (11), 129 (9), 78(base), 46 (38). Analysis for C20H18N4O4 (378.38), calculated C 63.49, H 4.79, N 14.81 %, found C 63.49, H 4.61, N 14.77 %.
detailsCrystal data, data collection and structure
details are summarized in Table 3. For both compounds, the C-bound H-atoms were included in calculated positions and treated as riding atoms: C—H = 0.93–0.98 Å with Uiso(H) = 1.5Ueq(C-methyl) and 1.2Ueq(C) for other H atoms. For compound (I), the (Parsons et al., 2013) is = -0.2 (10), but it has no physical meaning here.Data collection: STADI4 (Stoe & Cie, 1997) for (I); EXPOSE in IPDS-I (Stoe & Cie, 2004) for (II). Cell
STADI4 (Stoe & Cie, 1997) for (I); CELL in IPDS-I (Stoe & Cie, 2004) for (II). Data reduction: X-RED (Stoe & Cie, 1997) for (I); INTEGRATE in IPDS-I (Stoe & Cie, 2004) for (II). For both compounds, program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: PLATON (Spek, 2009) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015), PLATON (Spek, 2009) and publCIF (Westrip, 2010).Fig. 1. A view of the molecular structure of compound (I), showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. | |
Fig. 2. A view of the molecular structure of compound (II), showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Unlabelled atoms are related to labelled atoms by the symmetry code (-x + 2, -y + 3/2, z). | |
Fig. 3. A view along the a axis of the crystal packing of compound (I). The hydrogen bonds are shown as dashed lines (see Table 1; only H atom H11 has been included). | |
Fig. 4. A view along the a axis of the crystal packing of compound (II). The hydrogen bonds are shown as dashed lines (see Table 2; only H atom H7 has been included). | |
Fig. 5. The chemical scheme for compound L2H2. |
C18H14N4O4 | F(000) = 728 |
Mr = 350.33 | Dx = 1.428 Mg m−3 |
Monoclinic, Ia | Mo Kα radiation, λ = 0.71073 Å |
a = 8.4249 (12) Å | Cell parameters from 33 reflections |
b = 12.2465 (10) Å | θ = 14.1–19.6° |
c = 16.2561 (13) Å | µ = 0.10 mm−1 |
β = 103.730 (8)° | T = 293 K |
V = 1629.3 (3) Å3 | Rod, colourless |
Z = 4 | 0.70 × 0.50 × 0.38 mm |
Stoe–Siemens AED2 diffractometer | θmax = 25.5°, θmin = 2.1° |
ω/\2q scans | h = −10→10 |
3035 measured reflections | k = 0→14 |
3028 independent reflections | l = −19→19 |
2737 reflections with I > 2σ(I) | 2 standard reflections every 60 min |
Rint = 0.012 | intensity decay: 1% |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.050 | H-atom parameters constrained |
wR(F2) = 0.135 | w = 1/[σ2(Fo2) + (0.0759P)2 + 1.0624P] where P = (Fo2 + 2Fc2)/3 |
S = 1.11 | (Δ/σ)max < 0.001 |
3028 reflections | Δρmax = 0.19 e Å−3 |
238 parameters | Δρmin = −0.21 e Å−3 |
2 restraints | Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0065 (18) |
C18H14N4O4 | V = 1629.3 (3) Å3 |
Mr = 350.33 | Z = 4 |
Monoclinic, Ia | Mo Kα radiation |
a = 8.4249 (12) Å | µ = 0.10 mm−1 |
b = 12.2465 (10) Å | T = 293 K |
c = 16.2561 (13) Å | 0.70 × 0.50 × 0.38 mm |
β = 103.730 (8)° |
Stoe–Siemens AED2 diffractometer | Rint = 0.012 |
3035 measured reflections | 2 standard reflections every 60 min |
3028 independent reflections | intensity decay: 1% |
2737 reflections with I > 2σ(I) |
R[F2 > 2σ(F2)] = 0.050 | 2 restraints |
wR(F2) = 0.135 | H-atom parameters constrained |
S = 1.11 | Δρmax = 0.19 e Å−3 |
3028 reflections | Δρmin = −0.21 e Å−3 |
238 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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.8419 (5) | 1.1583 (3) | 0.0691 (2) | 0.0470 (9) | |
O2 | 1.0295 (4) | 1.1079 (3) | −0.0014 (2) | 0.0395 (8) | |
O3 | 1.0067 (5) | 1.1074 (3) | 0.3016 (2) | 0.0463 (10) | |
O4 | 1.1454 (4) | 1.1588 (3) | 0.2054 (2) | 0.0355 (8) | |
N1 | 0.9519 (4) | 0.8948 (3) | 0.0567 (2) | 0.0266 (8) | |
N2 | 1.0688 (4) | 0.8934 (3) | 0.2330 (2) | 0.0272 (8) | |
N3 | 1.0738 (4) | 0.6793 (3) | 0.3087 (2) | 0.0279 (8) | |
N4 | 0.8579 (5) | 0.6232 (3) | 0.0803 (2) | 0.0348 (9) | |
C1 | 0.9822 (5) | 0.8015 (3) | 0.0992 (2) | 0.0248 (9) | |
C2 | 0.9784 (5) | 0.9878 (3) | 0.1014 (2) | 0.0259 (9) | |
C3 | 1.0319 (5) | 0.9857 (3) | 0.1896 (3) | 0.0268 (9) | |
C4 | 1.0489 (5) | 0.8006 (3) | 0.1880 (2) | 0.0227 (8) | |
C5 | 1.1158 (5) | 0.6996 (3) | 0.2355 (2) | 0.0248 (9) | |
C6 | 1.2218 (5) | 0.6347 (4) | 0.2045 (3) | 0.0311 (9) | |
H6 | 1.2486 | 0.6520 | 0.1537 | 0.037* | |
C7 | 1.2879 (6) | 0.5430 (4) | 0.2500 (3) | 0.0349 (10) | |
H7 | 1.3595 | 0.4979 | 0.2303 | 0.042* | |
C8 | 1.2459 (6) | 0.5200 (3) | 0.3248 (3) | 0.0345 (10) | |
H8 | 1.2879 | 0.4589 | 0.3565 | 0.041* | |
C9 | 1.1394 (5) | 0.5903 (4) | 0.3517 (3) | 0.0312 (9) | |
H9 | 1.1118 | 0.5748 | 0.4025 | 0.037* | |
C10 | 0.9393 (5) | 0.6998 (3) | 0.0486 (2) | 0.0255 (9) | |
C11 | 0.9763 (6) | 0.6908 (4) | −0.0299 (3) | 0.0334 (10) | |
H11 | 1.0322 | 0.7464 | −0.0499 | 0.040* | |
C12 | 0.9291 (6) | 0.5984 (4) | −0.0777 (3) | 0.0389 (11) | |
H12 | 0.9543 | 0.5900 | −0.1301 | 0.047* | |
C13 | 0.8443 (7) | 0.5192 (4) | −0.0469 (3) | 0.0413 (12) | |
H13 | 0.8098 | 0.4561 | −0.0779 | 0.050* | |
C14 | 0.8113 (7) | 0.5353 (4) | 0.0320 (3) | 0.0439 (13) | |
H14 | 0.7529 | 0.4814 | 0.0524 | 0.053* | |
C15 | 0.9399 (6) | 1.0942 (4) | 0.0546 (3) | 0.0316 (10) | |
C16 | 1.0580 (5) | 1.0903 (4) | 0.2399 (3) | 0.0287 (9) | |
C17 | 1.0131 (8) | 1.2133 (4) | −0.0439 (3) | 0.0525 (14) | |
H17A | 1.0924 | 1.2190 | −0.0774 | 0.079* | |
H17B | 1.0307 | 1.2706 | −0.0024 | 0.079* | |
H17C | 0.9053 | 1.2199 | −0.0798 | 0.079* | |
C18 | 1.1672 (6) | 1.2674 (4) | 0.2412 (3) | 0.0386 (11) | |
H18A | 1.2114 | 1.3143 | 0.2049 | 0.058* | |
H18B | 1.2410 | 1.2645 | 0.2961 | 0.058* | |
H18C | 1.0636 | 1.2955 | 0.2464 | 0.058* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.054 (2) | 0.0354 (19) | 0.054 (2) | 0.0149 (17) | 0.0183 (17) | 0.0094 (17) |
O2 | 0.055 (2) | 0.0344 (19) | 0.0313 (17) | −0.0011 (15) | 0.0150 (15) | 0.0089 (14) |
O3 | 0.079 (3) | 0.0309 (19) | 0.037 (2) | −0.0093 (17) | 0.0314 (19) | −0.0065 (14) |
O4 | 0.0460 (18) | 0.0266 (17) | 0.0375 (16) | −0.0064 (13) | 0.0171 (14) | −0.0077 (13) |
N1 | 0.0339 (19) | 0.0234 (19) | 0.0235 (18) | −0.0009 (14) | 0.0084 (14) | 0.0004 (13) |
N2 | 0.0320 (19) | 0.027 (2) | 0.0231 (18) | −0.0006 (14) | 0.0081 (15) | −0.0003 (13) |
N3 | 0.0337 (19) | 0.0282 (19) | 0.0223 (18) | −0.0009 (15) | 0.0077 (14) | 0.0010 (14) |
N4 | 0.049 (2) | 0.0326 (19) | 0.0237 (17) | −0.0122 (17) | 0.0103 (16) | −0.0023 (16) |
C1 | 0.029 (2) | 0.025 (2) | 0.023 (2) | 0.0003 (16) | 0.0110 (17) | 0.0009 (16) |
C2 | 0.027 (2) | 0.027 (2) | 0.024 (2) | 0.0006 (17) | 0.0066 (16) | 0.0011 (16) |
C3 | 0.032 (2) | 0.023 (2) | 0.027 (2) | 0.0005 (17) | 0.0108 (18) | −0.0016 (16) |
C4 | 0.0233 (19) | 0.024 (2) | 0.022 (2) | −0.0001 (15) | 0.0082 (15) | 0.0013 (15) |
C5 | 0.029 (2) | 0.024 (2) | 0.0201 (19) | −0.0017 (16) | 0.0032 (16) | −0.0009 (16) |
C6 | 0.038 (2) | 0.029 (2) | 0.026 (2) | 0.0039 (19) | 0.0090 (18) | −0.0011 (18) |
C7 | 0.040 (2) | 0.027 (2) | 0.036 (2) | 0.0047 (19) | 0.006 (2) | −0.0035 (19) |
C8 | 0.043 (3) | 0.022 (2) | 0.034 (2) | 0.0019 (19) | 0.0007 (19) | 0.0013 (18) |
C9 | 0.038 (2) | 0.029 (2) | 0.024 (2) | −0.0046 (18) | 0.0027 (18) | 0.0040 (18) |
C10 | 0.031 (2) | 0.025 (2) | 0.020 (2) | 0.0015 (17) | 0.0040 (16) | 0.0015 (16) |
C11 | 0.042 (3) | 0.034 (2) | 0.026 (2) | −0.0032 (18) | 0.0130 (18) | −0.0015 (18) |
C12 | 0.053 (3) | 0.039 (3) | 0.026 (2) | 0.001 (2) | 0.013 (2) | −0.007 (2) |
C13 | 0.059 (3) | 0.032 (3) | 0.030 (2) | −0.003 (2) | 0.003 (2) | −0.0083 (19) |
C14 | 0.066 (3) | 0.031 (2) | 0.035 (3) | −0.018 (2) | 0.012 (2) | 0.002 (2) |
C15 | 0.038 (2) | 0.030 (2) | 0.023 (2) | −0.002 (2) | 0.0008 (17) | 0.0001 (17) |
C16 | 0.037 (2) | 0.022 (2) | 0.025 (2) | 0.0026 (17) | 0.0038 (17) | −0.0003 (17) |
C17 | 0.069 (4) | 0.039 (3) | 0.045 (3) | −0.012 (3) | 0.005 (3) | 0.017 (2) |
C18 | 0.047 (3) | 0.024 (2) | 0.046 (3) | −0.0043 (19) | 0.013 (2) | −0.006 (2) |
O1—C15 | 1.202 (6) | C6—C7 | 1.387 (6) |
O2—C15 | 1.324 (6) | C6—H6 | 0.9300 |
O2—C17 | 1.455 (5) | C7—C8 | 1.373 (7) |
O3—C16 | 1.200 (6) | C7—H7 | 0.9300 |
O4—C16 | 1.325 (6) | C8—C9 | 1.387 (7) |
O4—C18 | 1.446 (5) | C8—H8 | 0.9300 |
N1—C1 | 1.329 (5) | C9—H9 | 0.9300 |
N1—C2 | 1.340 (5) | C10—C11 | 1.388 (6) |
N2—C3 | 1.331 (6) | C11—C12 | 1.377 (7) |
N2—C4 | 1.341 (5) | C11—H11 | 0.9300 |
N3—C9 | 1.340 (5) | C12—C13 | 1.368 (7) |
N3—C5 | 1.343 (5) | C12—H12 | 0.9300 |
N4—C10 | 1.335 (6) | C13—C14 | 1.389 (7) |
N4—C14 | 1.336 (6) | C13—H13 | 0.9300 |
C1—C4 | 1.419 (5) | C14—H14 | 0.9300 |
C1—C10 | 1.489 (6) | C17—H17A | 0.9600 |
C2—C3 | 1.397 (5) | C17—H17B | 0.9600 |
C2—C15 | 1.505 (6) | C17—H17C | 0.9600 |
C3—C16 | 1.508 (6) | C18—H18A | 0.9600 |
C4—C5 | 1.495 (6) | C18—H18B | 0.9600 |
C5—C6 | 1.377 (6) | C18—H18C | 0.9600 |
C15—O2—C17 | 115.7 (4) | N4—C10—C11 | 123.2 (4) |
C16—O4—C18 | 116.2 (3) | N4—C10—C1 | 117.0 (3) |
C1—N1—C2 | 117.5 (3) | C11—C10—C1 | 119.7 (4) |
C3—N2—C4 | 116.6 (3) | C12—C11—C10 | 119.1 (4) |
C9—N3—C5 | 116.7 (4) | C12—C11—H11 | 120.5 |
C10—N4—C14 | 116.5 (4) | C10—C11—H11 | 120.5 |
N1—C1—C4 | 121.1 (4) | C13—C12—C11 | 118.8 (4) |
N1—C1—C10 | 116.2 (3) | C13—C12—H12 | 120.6 |
C4—C1—C10 | 122.7 (4) | C11—C12—H12 | 120.6 |
N1—C2—C3 | 120.9 (4) | C12—C13—C14 | 118.3 (4) |
N1—C2—C15 | 118.3 (3) | C12—C13—H13 | 120.9 |
C3—C2—C15 | 120.8 (4) | C14—C13—H13 | 120.9 |
N2—C3—C2 | 122.5 (4) | N4—C14—C13 | 124.2 (4) |
N2—C3—C16 | 116.7 (3) | N4—C14—H14 | 117.9 |
C2—C3—C16 | 120.8 (4) | C13—C14—H14 | 117.9 |
N2—C4—C1 | 121.1 (4) | O1—C15—O2 | 125.6 (4) |
N2—C4—C5 | 115.8 (3) | O1—C15—C2 | 122.9 (4) |
C1—C4—C5 | 122.8 (4) | O2—C15—C2 | 111.6 (4) |
N3—C5—C6 | 123.2 (4) | O3—C16—O4 | 126.2 (4) |
N3—C5—C4 | 117.7 (3) | O3—C16—C3 | 124.5 (4) |
C6—C5—C4 | 119.1 (4) | O4—C16—C3 | 109.4 (3) |
C5—C6—C7 | 119.0 (4) | O2—C17—H17A | 109.5 |
C5—C6—H6 | 120.5 | O2—C17—H17B | 109.5 |
C7—C6—H6 | 120.5 | H17A—C17—H17B | 109.5 |
C8—C7—C6 | 118.9 (4) | O2—C17—H17C | 109.5 |
C8—C7—H7 | 120.5 | H17A—C17—H17C | 109.5 |
C6—C7—H7 | 120.5 | H17B—C17—H17C | 109.5 |
C7—C8—C9 | 118.3 (4) | O4—C18—H18A | 109.5 |
C7—C8—H8 | 120.9 | O4—C18—H18B | 109.5 |
C9—C8—H8 | 120.9 | H18A—C18—H18B | 109.5 |
N3—C9—C8 | 123.9 (4) | O4—C18—H18C | 109.5 |
N3—C9—H9 | 118.1 | H18A—C18—H18C | 109.5 |
C8—C9—H9 | 118.1 | H18B—C18—H18C | 109.5 |
C2—N1—C1—C4 | −3.6 (5) | C5—N3—C9—C8 | 0.1 (6) |
C2—N1—C1—C10 | 175.4 (3) | C7—C8—C9—N3 | 0.4 (7) |
C1—N1—C2—C3 | −1.6 (5) | C14—N4—C10—C11 | −0.4 (7) |
C1—N1—C2—C15 | −178.2 (4) | C14—N4—C10—C1 | 176.0 (4) |
C4—N2—C3—C2 | −1.4 (5) | N1—C1—C10—N4 | −133.7 (4) |
C4—N2—C3—C16 | −178.6 (4) | C4—C1—C10—N4 | 45.3 (5) |
N1—C2—C3—N2 | 4.3 (6) | N1—C1—C10—C11 | 42.8 (5) |
C15—C2—C3—N2 | −179.2 (4) | C4—C1—C10—C11 | −138.2 (4) |
N1—C2—C3—C16 | −178.6 (4) | N4—C10—C11—C12 | −0.7 (7) |
C15—C2—C3—C16 | −2.1 (6) | C1—C10—C11—C12 | −177.0 (4) |
C3—N2—C4—C1 | −3.8 (5) | C10—C11—C12—C13 | 1.2 (7) |
C3—N2—C4—C5 | 170.5 (3) | C11—C12—C13—C14 | −0.6 (8) |
N1—C1—C4—N2 | 6.5 (5) | C10—N4—C14—C13 | 1.0 (8) |
C10—C1—C4—N2 | −172.4 (4) | C12—C13—C14—N4 | −0.5 (8) |
N1—C1—C4—C5 | −167.4 (4) | C17—O2—C15—O1 | 4.4 (7) |
C10—C1—C4—C5 | 13.7 (5) | C17—O2—C15—C2 | −174.1 (4) |
C9—N3—C5—C6 | −0.6 (6) | N1—C2—C15—O1 | 120.0 (5) |
C9—N3—C5—C4 | −177.9 (4) | C3—C2—C15—O1 | −56.6 (6) |
N2—C4—C5—N3 | 50.7 (5) | N1—C2—C15—O2 | −61.5 (5) |
C1—C4—C5—N3 | −135.1 (4) | C3—C2—C15—O2 | 121.9 (4) |
N2—C4—C5—C6 | −126.6 (4) | C18—O4—C16—O3 | −6.2 (7) |
C1—C4—C5—C6 | 47.6 (6) | C18—O4—C16—C3 | 173.9 (4) |
N3—C5—C6—C7 | 0.7 (7) | N2—C3—C16—O3 | −50.9 (6) |
C4—C5—C6—C7 | 177.9 (4) | C2—C3—C16—O3 | 131.8 (5) |
C5—C6—C7—C8 | −0.2 (7) | N2—C3—C16—O4 | 128.9 (4) |
C6—C7—C8—C9 | −0.4 (7) | C2—C3—C16—O4 | −48.3 (5) |
Cg2 is the centroid of the N3/C5–C9 pyridine ring. |
D—H···A | D—H | H···A | D···A | D—H···A |
C11—H11···N3i | 0.93 | 2.57 | 3.334 (5) | 140 |
C7—H7···Cg2ii | 0.93 | 2.95 | 3.742 (5) | 144 |
C17—H17C···Cg2iii | 0.96 | 2.92 | 3.722 (6) | 141 |
Symmetry codes: (i) x, −y+3/2, z−1/2; (ii) x+1/2, −y+1, z; (iii) x−1/2, y+3/2, z−1/2. |
C20H18N4O4 | Dx = 1.324 Mg m−3 |
Mr = 378.38 | Mo Kα radiation, λ = 0.71073 Å |
Tetragonal, I41/a | Cell parameters from 5000 reflections |
a = 10.2295 (6) Å | θ = 3.3–52.1° |
c = 36.281 (3) Å | µ = 0.10 mm−1 |
V = 3796.5 (5) Å3 | T = 223 K |
Z = 8 | Block, colourless |
F(000) = 1584 | 0.65 × 0.50 × 0.50 mm |
Stoe IPDS 1 diffractometer | 1153 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.043 |
Plane graphite monochromator | θmax = 26.0°, θmin = 2.1° |
φ rotation scans | h = −12→12 |
14760 measured reflections | k = −12→12 |
1851 independent reflections | l = −44→44 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.049 | H-atom parameters constrained |
wR(F2) = 0.149 | w = 1/[σ2(Fo2) + (0.0925P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.01 | (Δ/σ)max < 0.001 |
1851 reflections | Δρmax = 0.34 e Å−3 |
129 parameters | Δρmin = −0.19 e Å−3 |
0 restraints | Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0049 (10) |
C20H18N4O4 | Z = 8 |
Mr = 378.38 | Mo Kα radiation |
Tetragonal, I41/a | µ = 0.10 mm−1 |
a = 10.2295 (6) Å | T = 223 K |
c = 36.281 (3) Å | 0.65 × 0.50 × 0.50 mm |
V = 3796.5 (5) Å3 |
Stoe IPDS 1 diffractometer | 1153 reflections with I > 2σ(I) |
14760 measured reflections | Rint = 0.043 |
1851 independent reflections |
R[F2 > 2σ(F2)] = 0.049 | 0 restraints |
wR(F2) = 0.149 | H-atom parameters constrained |
S = 1.01 | Δρmax = 0.34 e Å−3 |
1851 reflections | Δρmin = −0.19 e Å−3 |
129 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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.7424 (2) | 0.7559 (3) | 0.00480 (5) | 0.1009 (9) | |
O2 | 0.91015 (17) | 0.64422 (18) | −0.01674 (4) | 0.0693 (5) | |
N1 | 0.86590 (16) | 0.73125 (18) | 0.07318 (4) | 0.0478 (5) | |
N2 | 0.88149 (17) | 0.8399 (2) | 0.16340 (5) | 0.0583 (6) | |
C1 | 0.9332 (2) | 0.7371 (2) | 0.04156 (5) | 0.0473 (5) | |
C2 | 0.93113 (19) | 0.7446 (2) | 0.10488 (5) | 0.0450 (5) | |
C3 | 0.84753 (19) | 0.7504 (2) | 0.13824 (5) | 0.0452 (5) | |
C4 | 0.7388 (2) | 0.6719 (2) | 0.14134 (5) | 0.0466 (5) | |
H4 | 0.7174 | 0.6124 | 0.1225 | 0.056* | |
C5 | 0.6613 (2) | 0.6817 (2) | 0.17249 (5) | 0.0503 (5) | |
H5 | 0.5874 | 0.6282 | 0.1755 | 0.060* | |
C6 | 0.6952 (2) | 0.7712 (2) | 0.19868 (6) | 0.0569 (6) | |
H6 | 0.6448 | 0.7803 | 0.2202 | 0.068* | |
C7 | 0.8042 (2) | 0.8481 (3) | 0.19322 (6) | 0.0637 (7) | |
H7 | 0.8256 | 0.9098 | 0.2114 | 0.076* | |
C8 | 0.8508 (2) | 0.7155 (3) | 0.00796 (5) | 0.0558 (6) | |
C9 | 0.8402 (3) | 0.6183 (4) | −0.05106 (7) | 0.0978 (11) | |
H9A | 0.7744 | 0.5501 | −0.0471 | 0.117* | |
H9B | 0.7956 | 0.6977 | −0.0594 | 0.117* | |
C10 | 0.9335 (4) | 0.5760 (3) | −0.07867 (8) | 0.0965 (11) | |
H10A | 0.8877 | 0.5552 | −0.1013 | 0.145* | |
H10B | 0.9793 | 0.4990 | −0.0699 | 0.145* | |
H10C | 0.9960 | 0.6455 | −0.0833 | 0.145* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0662 (13) | 0.187 (2) | 0.0499 (11) | 0.0406 (14) | −0.0132 (9) | −0.0026 (12) |
O2 | 0.0689 (11) | 0.0889 (12) | 0.0500 (9) | 0.0023 (9) | −0.0168 (8) | −0.0172 (8) |
N1 | 0.0424 (9) | 0.0665 (12) | 0.0347 (9) | 0.0012 (8) | −0.0018 (7) | 0.0026 (8) |
N2 | 0.0464 (10) | 0.0866 (14) | 0.0418 (9) | −0.0104 (10) | 0.0042 (8) | −0.0093 (9) |
C1 | 0.0440 (10) | 0.0630 (13) | 0.0348 (10) | 0.0039 (10) | −0.0018 (8) | 0.0012 (9) |
C2 | 0.0418 (10) | 0.0581 (13) | 0.0350 (10) | −0.0016 (9) | −0.0010 (8) | 0.0011 (9) |
C3 | 0.0379 (10) | 0.0629 (13) | 0.0348 (10) | 0.0007 (9) | −0.0026 (8) | 0.0026 (9) |
C4 | 0.0421 (11) | 0.0541 (12) | 0.0437 (11) | 0.0028 (9) | −0.0017 (8) | 0.0041 (9) |
C5 | 0.0407 (11) | 0.0630 (13) | 0.0471 (12) | 0.0017 (10) | 0.0035 (9) | 0.0086 (10) |
C6 | 0.0450 (12) | 0.0826 (17) | 0.0431 (11) | 0.0052 (12) | 0.0067 (9) | 0.0062 (11) |
C7 | 0.0553 (14) | 0.0941 (18) | 0.0416 (11) | −0.0080 (13) | 0.0046 (10) | −0.0127 (12) |
C8 | 0.0467 (13) | 0.0851 (17) | 0.0357 (11) | 0.0035 (12) | −0.0008 (9) | 0.0047 (11) |
C9 | 0.095 (2) | 0.141 (3) | 0.0578 (16) | −0.007 (2) | −0.0290 (15) | −0.0268 (18) |
C10 | 0.157 (3) | 0.0720 (18) | 0.0605 (17) | −0.020 (2) | −0.0135 (19) | −0.0139 (14) |
O1—C8 | 1.189 (3) | C4—H4 | 0.9400 |
O2—C8 | 1.305 (3) | C5—C6 | 1.364 (3) |
O2—C9 | 1.460 (3) | C5—H5 | 0.9400 |
N1—C2 | 1.337 (2) | C6—C7 | 1.379 (3) |
N1—C1 | 1.339 (2) | C6—H6 | 0.9400 |
N2—C3 | 1.339 (3) | C7—H7 | 0.9400 |
N2—C7 | 1.343 (3) | C9—C10 | 1.450 (5) |
C1—C1i | 1.392 (4) | C9—H9A | 0.9800 |
C1—C8 | 1.499 (3) | C9—H9B | 0.9800 |
C2—C2i | 1.413 (4) | C10—H10A | 0.9700 |
C2—C3 | 1.483 (3) | C10—H10B | 0.9700 |
C3—C4 | 1.377 (3) | C10—H10C | 0.9700 |
C4—C5 | 1.384 (3) | ||
C8—O2—C9 | 117.3 (2) | C7—C6—H6 | 120.4 |
C2—N1—C1 | 118.40 (17) | N2—C7—C6 | 123.8 (2) |
C3—N2—C7 | 116.06 (19) | N2—C7—H7 | 118.1 |
N1—C1—C1i | 120.88 (11) | C6—C7—H7 | 118.1 |
N1—C1—C8 | 113.63 (18) | O1—C8—O2 | 124.2 (2) |
C1i—C1—C8 | 125.48 (12) | O1—C8—C1 | 123.5 (2) |
N1—C2—C2i | 120.38 (11) | O2—C8—C1 | 112.27 (19) |
N1—C2—C3 | 114.72 (17) | C10—C9—O2 | 108.7 (3) |
C2i—C2—C3 | 124.88 (11) | C10—C9—H9A | 109.9 |
N2—C3—C4 | 123.56 (18) | O2—C9—H9A | 109.9 |
N2—C3—C2 | 115.71 (18) | C10—C9—H9B | 109.9 |
C4—C3—C2 | 120.65 (18) | O2—C9—H9B | 109.9 |
C3—C4—C5 | 119.1 (2) | H9A—C9—H9B | 108.3 |
C3—C4—H4 | 120.4 | C9—C10—H10A | 109.5 |
C5—C4—H4 | 120.4 | C9—C10—H10B | 109.5 |
C6—C5—C4 | 118.2 (2) | H10A—C10—H10B | 109.5 |
C6—C5—H5 | 120.9 | C9—C10—H10C | 109.5 |
C4—C5—H5 | 120.9 | H10A—C10—H10C | 109.5 |
C5—C6—C7 | 119.20 (19) | H10B—C10—H10C | 109.5 |
C5—C6—H6 | 120.4 | ||
C2—N1—C1—C1i | −3.1 (4) | C3—C4—C5—C6 | 1.1 (3) |
C2—N1—C1—C8 | 177.7 (2) | C4—C5—C6—C7 | 0.1 (3) |
C1—N1—C2—C2i | −4.4 (4) | C3—N2—C7—C6 | −0.2 (4) |
C1—N1—C2—C3 | 174.09 (19) | C5—C6—C7—N2 | −0.6 (4) |
C7—N2—C3—C4 | 1.6 (3) | C9—O2—C8—O1 | 3.0 (4) |
C7—N2—C3—C2 | 178.3 (2) | C9—O2—C8—C1 | −179.0 (2) |
N1—C2—C3—N2 | −137.7 (2) | N1—C1—C8—O1 | 37.9 (4) |
C2i—C2—C3—N2 | 40.8 (4) | C1i—C1—C8—O1 | −141.2 (3) |
N1—C2—C3—C4 | 39.1 (3) | N1—C1—C8—O2 | −140.1 (2) |
C2i—C2—C3—C4 | −142.4 (3) | C1i—C1—C8—O2 | 40.8 (4) |
N2—C3—C4—C5 | −2.1 (3) | C8—O2—C9—C10 | 162.0 (3) |
C2—C3—C4—C5 | −178.62 (19) |
Symmetry code: (i) −x+2, −y+3/2, z. |
Cg1 and Cg2 are the centroids of the pyrazine and pyridine rings N1/C1/C2/N1'/C1'/C2' and N2/C3–C7, respectively [symmetry code ('): -x + 2, -y + 3/2, z]. |
D—H···A | D—H | H···A | D···A | D—H···A |
C7—H7···O1ii | 0.94 | 2.48 | 3.308 (3) | 147 |
C4—H4···Cg2iii | 0.94 | 2.92 | 3.739 (2) | 147 |
C10—H10B···Cg1iv | 0.97 | 2.56 | 3.409 (3) | 146 |
C10—H10B···Cg1v | 0.97 | 2.56 | 3.409 (3) | 146 |
Symmetry codes: (ii) −y+7/4, x+1/4, z+1/4; (iii) y−1/4, −x+5/4, −z+1/4; (iv) −x+2, −y+1, −z; (v) x, y−1/2, −z. |
Cg2 is the centroid of the N3/C5–C9 pyridine ring. |
D—H···A | D—H | H···A | D···A | D—H···A |
C11—H11···N3i | 0.93 | 2.57 | 3.334 (5) | 140 |
C7—H7···Cg2ii | 0.93 | 2.95 | 3.742 (5) | 144 |
C17—H17C···Cg2iii | 0.96 | 2.92 | 3.722 (6) | 141 |
Symmetry codes: (i) x, −y+3/2, z−1/2; (ii) x+1/2, −y+1, z; (iii) x−1/2, y+3/2, z−1/2. |
Cg1 and Cg2 are the centroids of the pyrazine and pyridine rings N1/C1/C2/N1'/C1'/C2' and N2/C3–C7, respectively [symmetry code ('): -x + 2, -y + 3/2, z]. |
D—H···A | D—H | H···A | D···A | D—H···A |
C7—H7···O1i | 0.94 | 2.48 | 3.308 (3) | 147 |
C4—H4···Cg2ii | 0.94 | 2.92 | 3.739 (2) | 147 |
C10—H10B···Cg1iii | 0.97 | 2.56 | 3.409 (3) | 146 |
C10—H10B···Cg1iv | 0.97 | 2.56 | 3.409 (3) | 146 |
Symmetry codes: (i) −y+7/4, x+1/4, z+1/4; (ii) y−1/4, −x+5/4, −z+1/4; (iii) −x+2, −y+1, −z; (iv) x, y−1/2, −z. |
Experimental details
(I) | (II) | |
Crystal data | ||
Chemical formula | C18H14N4O4 | C20H18N4O4 |
Mr | 350.33 | 378.38 |
Crystal system, space group | Monoclinic, Ia | Tetragonal, I41/a |
Temperature (K) | 293 | 223 |
a, b, c (Å) | 8.4249 (12), 12.2465 (10), 16.2561 (13) | 10.2295 (6), 10.2295 (6), 36.281 (3) |
α, β, γ (°) | 90, 103.730 (8), 90 | 90, 90, 90 |
V (Å3) | 1629.3 (3) | 3796.5 (5) |
Z | 4 | 8 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 0.10 | 0.10 |
Crystal size (mm) | 0.70 × 0.50 × 0.38 | 0.65 × 0.50 × 0.50 |
Data collection | ||
Diffractometer | Stoe–Siemens AED2 | Stoe IPDS 1 |
Absorption correction | – | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3035, 3028, 2737 | 14760, 1851, 1153 |
Rint | 0.012 | 0.043 |
(sin θ/λ)max (Å−1) | 0.606 | 0.616 |
Refinement | ||
R[F2 > 2σ(F2)], wR(F2), S | 0.050, 0.135, 1.11 | 0.049, 0.149, 1.01 |
No. of reflections | 3028 | 1851 |
No. of parameters | 238 | 129 |
No. of restraints | 2 | 0 |
H-atom treatment | H-atom parameters constrained | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.19, −0.21 | 0.34, −0.19 |
Computer programs: STADI4 (Stoe & Cie, 1997), EXPOSE in IPDS-I (Stoe & Cie, 2004), CELL in IPDS-I (Stoe & Cie, 2004), X-RED (Stoe & Cie, 1997), INTEGRATE in IPDS-I (Stoe & Cie, 2004), SHELXS97 (Sheldrick, 2008), PLATON (Spek, 2009) and Mercury (Macrae et al., 2008), SHELXL2014 (Sheldrick, 2015), PLATON (Spek, 2009) and publCIF (Westrip, 2010).
Acknowledgements
We are grateful to the Swiss National Science Foundation and the University of Neuchâtel for financial support.
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