Smaller is smarter in a new cobalt(II) imide: intermolecular interactions
involving pyrazine versus the larger aromatic quinoxaline
Matthew G. Cowan, Reece G. Miller, and Sally Brooker*
Department of Chemistry and the MacDiarmid Institute for Advanced Materials and
Nanotechnology, University of Otago, PO Box 56, Dunedin 9054, New Zealand. Email: sbrooker@chemistry.otago.ac.nz; Fax: +64-3-479 7906; Tel: +64-3-479 7919
An invited submission to this special Australasian issue.
Electronic Supporting Information
Additional synthetic details
Preparation of 2-styrylquinoxaline (prepared according to ref 1)
A mixture of 2-methylquinoxaline (5.2 g, 36.1 mmol), benzaldehyde (12.14 g, 114 mmol), acetic
anhydride (12 mL, 12.8 mmol) and sodium hydroxide (0.4 g, 10 mmol) was heated to 125 °C for
18 hours. The reaction was cooled and an excess of freshly prepared concentrated sodium
hydroxide was added. The resulting solution was extracted with diethylether (4 x 20 mL), the
combined extracts washed with water (3 x 10 mL) and then evaporated under reduced pressure to
give a thick oil. The unreacted starting materials were removed by Kugelrohr distillation under
high vacuum at 120 °C. The product was then collected by Kugelrohr distillation under high
vacuum at 200 °C. The resulting yellow oil was recrystallised from methanol and collected as
yellow crystals (4.237 g, 51%). MS (+ESI)(CH2Cl2): m/z 233.1069 [C16H13N2]+ calc. 233.1073.
1
H NMR (400 MHz, CDCl3): δ (ppm) 9.054 (s, 1H, H5), 8.077 (dt, J1-2/4-3 = 8.4 Hz, J1-3/4-2 = 1.6
Hz, 1H, H1/4), 7.769 (td, J2-1 = 6.8 Hz, J2-4 = 1.6 Hz, 1H, H2), 7.713 (td, J3-4 = 6.8 Hz, J3-1 = 1.6
Hz, 1H, H3), 7.886 (d, J = 16.4 Hz, 1H, H6), 7.673 (d, J = 8.8 Hz, 2H, H8/12), 7.452-7.418 (m,
3H, H9-11), 7.397 (d, J = 16.4 Hz, 1H, H7).
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Preparation of 2-quinoxalinecarboxylic acid (prepared according to ref1)
Potassium permanganate (374.6 mg, 2.63 mmol) was slowly added (ca. 20 minutes) to a solution
of 2-styrylquinoxaline (200 mg, 0.858 mmol) in acetone (7 mL). The resulting suspension was
stirred for two hours then filtered through celite and washed with hot water (80 mL). The
combined filtrate was evaporated to approximately 20 mL under reduced pressure and
concentrated hydrochloric acid (5 mL) was added and the product co-crystallised with benzoic
acid as white crystals. The crystals were collected and washed with diethylether (3 x 10 mL) to
remove the benzoic acid, leaving the product as a white solid (109.7 mg, 73%).1H NMR (400
MHz, CDCl3): δ (ppm) 9.567 (s, 1H, H5), 8.342 (dd, J1-2 = 8 Hz, J1-3 = 2 Hz, 1H, H1), 8.284 (dd,
J4-3 = 8 Hz, J4-2 = 0.8 Hz, 1H, H4), 7.938 (q-br, J2/3-3/2/1/4 = 8.4 Hz 2H, H4).
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Additional structural details
Table S1. Crystal structure determination details for Hquinoxquinox∙DMSO and [CoII(quinoxpz)2]∙CH3OH.
Hquinoxquinox∙DMSO
[CoII(quinoxpz)2]∙CH3OH
Empirical formula
C20H17N5O3S
C28.25H17CoN10O4.25
Formula weight
407.45
623.45
Temperature
90(2) K
90(2) K
Wavelength
0.71073 Å
0.71073 Å
Crystal system
Orthorhombic
Triclinic
Space group
Pca21
P-1
a
21.801(2) Å
10.3876(19) Å
b
5.6444(6) Å
11.573(2) Å
c
15.104(2) Å
12.311(2) Å
α
90°
95.091(10)°
β
90°
93.841(10)°
γ
90°
112.259(9)°
Volume
1858.6(4) Å3
1356.2(4) Å3
Z
4
2
-1
Density (calculated)
1.456 g cm
1.527 g cm-1
Absorption coefficient
0.208 mm-1
0.690 mm-1
F(000)
848
635
Crystal size
0.3 x 0.2 x 0.05 mm3
0.2 x 0.2 x 0.2 mm3
Theta range for data collection
3.97 to 26.40°
1.92 to 26.44°
Index ranges
-27 ≤ h ≤ 27, -7 ≤ k ≤ 6, -16 ≤ l ≤ 18
-12 ≤ h ≤ 12, -14 ≤ k ≤ 14, -15 ≤ l ≤ 15
Reflections collected
13105
32024
Independent reflections
3466 [Rint = 0.0980]
5532 [Rint = 0.0542]
Completeness to theta = 26.40°
99.3%
99.0%
Absorption correction
Semi-empirical from equivalents
Semi-empirical from equivalents
Max. and min. transmission
0.7454 and 0.6210
0.7454 and 0.6773
Refinement method
Full-matrix least-squares on F
Data / restraints / parameters
2
Full-matrix least-squares on F2
3466 / 1 / 267
5532 / 1 / 397
1.070
1.074
Final R indices [I>2sigma(I)]
R1 = 0.0669, wR2 = 0.1344
R1 = 0.0674, wR2 = 0.1850
R indices (all data)
R1 = 0.0975, wR2 = 0.1468
R1 = 0.0831, wR2 = 0.1952
Absolute structure parameter
-0.03(15)
-
Largest diff. peak and hole
0.360 and -0.305 e Å-3
1.672 and -0.410 e Å-3
Goodness-of-fit on F
2
S3
Additional structural diagrams
Figure S1. The H-bonding interactions observed between the ligand Hquinoxquinox and d6-DMSO. Distances
shown between non-H atoms, but clearly the H atoms are involved in the H-bonds (O21∙∙∙C7: 3.264 Å, 157.7°;
O21∙∙∙C16: 3.124 Å, 134.3°; C22∙∙∙O1: 3.476 Å, 150.9°, C15∙∙∙N2A = 3.480 Å, 157.3°).
S4
Figure S2. Two views of the offset π-π stacking interaction observed between the quinoxaline moieties in adjacent
ligand molecules in Hquinoxquinox·d6-DMSO, that connects the chains of H-bonded Hquinoxquinox molecules
in the third-dimension (solvent omitted for clarity). Top: centroidC13-C18∙∙∙centroidN1-N2: 3.612 Å, offset 6.1°.
Bottom: π-stacking viewed perpendicular to the N1-N2 aromatic ring.
S5
Figure S3. The short contact between the imide carbonyl atom and the d 6-DMSO oxygen atom (C22∙∙∙O21: 3.164 Å)
in Hquinoxquinox.
S6
Figure S4. The cage formed around the disordered methanol molecule in [CoII(quinoxpz)2]∙CH3OH. Note that nonsolvent hydrogen atoms have been omitted for clarity.
S7
Figure S5. The π-π interactions (centroidC1-C4∙∙∙centroidC1’-C4’ 3.369 Å; centroidC21-C24∙∙∙centroidC21’-C24’ 3.499 Å) and
‘edge to face’ π-stacking interactions (N2∙∙∙centroidC27-C34 2.978 Å) connecting the walls of the ‘cage’ (Figure S4) in
[CoII(quinoxpz)2]∙CH3OH. Note that non-solvent hydrogen atoms have been omitted for clarity.
S8
Figure S6. The mutual intermolecular head-to-tail bifurcated hydrogen bonding (C21∙∙∙O1/O2: 3.207/3.267 Å;
C21∙∙∙H21∙∙∙O2/O1: 153.6/130.3) connecting adjacent [CoII(quinoxpz)2] complexes in [CoII(quinoxpz)2]∙CH3OH.
Note that these interactions are reinforced by carbonyl-carbonyl stacking interactions (Figure S7). H atoms involved
in hydrogen bonding are shown in black.
S9
Figure S7. The mutual intermolecular carbonyl-carbonyl stacking interactions connecting adjacent
[CoII(quinoxpz)2] complexes (O1∙∙∙C6’: 3.135 Å and O2∙∙∙C5’: 3.116 Å) in [CoII(quinoxpz)2]∙CH3OH. Note that
these interactions are reinforced by head-to-tail bifurcated hydrogen bonding interactions (Figure S6).
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Figure S8. Inter-ligand cis-angles between the ‘spare’ quinoxaline and pyrazine nitrogen atoms.
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Figure S9. 1H NMR spectra (400 MHz) of Hquinoxpz in CDCl3. Please note the peak at δ = 1.64 ppm is
HDO.
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Figure S10. 1H NMR spectra (400 MHz) of Hquinoxquinox in CDCl3. Note that the poor signal to noise ratio
is due to the low solubility of the ligand.
S13
Reference
(1)
von Keller-Schierlein, W.; Prelog, V. Helv. Chim. Acta. 1957, 60, 205.
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