1-(Imidazo[1,2-a]pyridin-1-ium-1-yl)-2,3,4-trioxocyclobutan-1-ide

Kunick, Conrad; Jones, Peter G.

doi:10.3390/m1072

Cited by 2 publications

(5 citation statements)

References 10 publications

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“…These geometric parameters indicate that the resonance hybrid structure IV in Scheme 1 is the predominant form rather than the N-ylide structure II. This is consistent with previous structure reports of betaines of squaric acid containing a threecoordinate nitrogen atom [11][12][13][14][15][16][17] and the triphenylphosphonium betaine (CSD refcode: PIDDEL) [18], the only previously reported structurally characterized betaine of squaric acid featuring a four-coordinate group 15 atom. The CSD entry FEFLEI as an exception exhibits slightly different lateral C−O bond lengths, obviously resulting from intramolecular hydrogen bonding [19].…”

Section: Structural Description Of 1 In the Solid-statesupporting

confidence: 92%

“…0.12 Å, reflecting the squaramide nature of these structures [20][21][22][23]. The C4−C1−C2 bond angle in 1 is comparable to the average of the corresponding bond angle of 96.2° of the aforementioned previously reported betaines [11][12][13][14][15][16][17]19]. In PID-DEL, the corresponding angle is markedly smaller at 94.6 (1)° [18].…”

Section: Structural Description Of 1 In the Solid-statesupporting

confidence: 68%

“…The C1−N1 bond in 1 is longer by ca. 0.05 Å than the average C−N(sp 2 ) bond length in betaines of squaric acid with a three-coordinate nitrogen atom [11][12][13][14][15][16][17]19], but as expected markedly shorter by ca. 0.30 Å than the corresponding C−P bond in PIDDEL.…”

Section: Structural Description Of 1 In the Solid-statesupporting

confidence: 52%

“…Consistent with local C 2v symmetry, three 13 C NMR signals arise from the C 4 O 3 unit (Figure 5 and Table 4). For the related 2-imidazol [1,2-a]pyridine of squaric acid, similar 13 C NMR shifts have been reported for these carbon atoms but assignments have not been made [14]. We assign the signal with the largest downfield shift (211.0 ppm) to C3.…”

Section: Nmr Spectroscopymentioning

confidence: 54%

“…Molbank 2023, 2023, x FOR PEER REVIEW 6 of 10 related 2-imidazol [1,2-a]pyridine of squaric acid, similar 13 C NMR shifts have been reported for these carbon atoms but assignments have not been made [14]. We assign the signal with the largest downfield shift (211.0 ppm) to C3.…”

Section: Nmr Spectroscopymentioning

confidence: 62%

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Structural Elucidation of the Triethylammonium Betaine of Squaric Acid

Palme,

Goddard,

Leutzsch

et al. 2023

Molbank

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Betaines of squaric acid have gained research interest because of their structural and spectral properties. We elucidated the crystal and molecular structure of the triethylammonium betaine of squaric acid (1) by X-ray crystallography, IR, and NMR spectroscopy augmented by Hirshfeld surface analysis and DFT calculations. The crystal structure determination using Hirshfeld atom refinement reveals that the resonance hybrid structure with partial enolate character of the two lateral squaric acid C=O groups describes 1 best. The solid-state supramolecular structure features weak intermolecular C−H···O hydrogen bonds. The number of C=O bands in the IR spectrum in the solid-state is consistent with local C2v symmetry of the squaric acid residue in 1. The 13C NMR signals of this group in solution were assigned based on 2D NMR experiments and computational prediction using the Gauge-Independent Atom Orbital (GIAO) method. The present study provides the first structural characterization of a betaine of squaric acid containing a four-coordinate nitrogen atom directly attached to the four-membered ring.

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