Nitrogen heterocycles are a class of organic compounds with extremely versatile functionality. Imidines, HN[C(NH) R ] 2 , are a rare class of heterocycles related to imides, HN[C(O) R ] 2 , in which the O atoms of the carbonyl groups are replaced by N—H groups. The useful synthesis of the imidine compounds succinimidine and glutarimidine, as well as their partially hydrolyzed imino–imide congeners, was first described in the mid-1950s, though structural characterization is presented for the first time in this article. In the solid state, these structures are different from the proposed imidine form: succinimidine crystallizes as an imino–amine, 2-imino-3,4-dihydro-2 H -pyrrol-5-amine, C 4 H 7 N 2 ( 1 ), glutarimidine as 6-imino-3,4,5,6-tetrahydropyridin-2-amine methanol monosolvate, C 5 H 9 N 3 ·CH 3 OH ( 2 ), and the corresponding hydrolyzed imino–imide compounds as amino–amides 5-amino-3,4-dihydro-2 H -pyrrol-2-one, C 4 H 6 N 2 O ( 3 ), and 6-amino-4,5-dihydropyridin-2(3 H )-one, C 5 H 8 N 2 O ( 4 ). Imidine 1 was also determined as the hydrochloride salt solvate 5-amino-3,4-dihydro-2 H -pyrrol-2-iminium chloride–2-imino-3,4-dihydro-2 H -pyrrol-5-amine–water (1/1/1), C 4 H 8 N 3 + ·Cl − ·C 4 H 7 N 3 ·H 2 O ( 1 ·HCl). As such, 1 and 2 show alternating short and long C—N bonds across the molecule, revealing distinct imino (C=NH) and amine (C—NH 2 ) groups throughout the C—N backbone. These structures provide definitive evidence for the predominant imino–amine tautomer in the solid state, which serves to enrich the previously proposed imidine-focused structures that have appeared in organic chemistry textbooks since the discovery of this class of compounds in 1883.
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Crystal structures of sodium-, lithium-, and ammonium 4,5-dihydroxybenzene-1,3-disulfonate (tiron) hydrates
The solid-state structures of the Na + , Li + , and NH 4 + salts of the 4,5-dihydroxybenzene-1,3-disulfonate (tiron) dianion are reported, namely disodium 4,5-dihydroxybenzene-1,3-disulfonate, 2Na + ·C 6 H 4 O 8 S 2 2− , μ-4,5-dihydroxybenzene-1,3-disulfonato-bis[aqualithium(I)] hemihydrate, [Li 2 (C 6 H 4 O 8 S 2 )(H 2 O) 2 ]·0.5H 2 O, and diammonium 4,5-dihydroxybenzene-1,3-disulfonate monohydrate, 2NH 4 + ·C 6 H 4 O 8 S 2 2− ·H 2 O. Intermolecular interactions vary with the size of the cation, and the asymmetric unit cell, and the macromolecular features are also affected. The sodium in Na 2 (tiron) is coordinated in a distorted octahedral environment through the sulfonate oxygen and hydroxyl oxygen donors on tiron, as well as an interstitial water molecule. Lithium, with its smaller ionic radius, is coordinated in a distorted tetrahedral environment by sulfonic and phenolic O atoms, as well as water in Li 2 (tiron). The surrounding tiron anions coordinating to sodium or lithium in Na 2 (tiron) and Li 2 (tiron), respectively, result in a three-dimensional network held together by the coordinate bonds to the alkali metal cations. The formation of such a three-dimensional network for tiron salts is relatively rare and has not been observed with monovalent cations. Finally, (NH 4 ) 2 (tiron) exhibits extensive hydrogen-bonding arrays between NH 4 + and the surrounding tiron anions and interstitial water molecules. This series of structures may be valuable for understanding charge transfer in a putative solid-state fuel cell utilizing tiron.
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- Award ID(s):
- 1708793
- NSF-PAR ID:
- 10073869
- Date Published:
- Journal Name:
- Acta Crystallographica Section E Crystallographic Communications
- Volume:
- 74
- Issue:
- 7
- ISSN:
- 2056-9890
- Page Range / eLocation ID:
- 918 to 925
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1107/S2056989018008009
