<sup>13</sup>C‐NMR. Spectra, Structure and Reactivity of Cyclic Oxocarbons

Städeli, Werner; Hollenstein, Roger; Philipsborn, W. Von

doi:10.1002/hlca.19770600325

Cited by 33 publications

(13 citation statements)

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“…C NMR spectra of croconic acid have long been studied (2). In aqueous solution some of the carbonyl groups become hydrated and an equilibrium can be observed between the various hydrated forms.…”

Section: Photochemical Oxidationmentioning

confidence: 99%

“…4,5-Dihydroxycyclopentenetrione 1, commonly known as "croconic" acid, H2C505, and the croconate anion [C,O,]~-have received considerable attention from both a theoretical and an experimental point of view (1)(2)(3)(4)(5)(6). Croconate, like squarate or rhodizonate ions, is a member of the oxocarbon ring system, [cn0,12-, a new class of aromatic substances with planar structure containing only carbon and oxygen atoms.…”

mentioning

confidence: 99%

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A photo-oxidation of croconic acid into oxalic acid

Fabre¹,

Castan²,

Deguenon³

et al. 1995

Can. J. Chem.

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Croconic acid, H2C5O5. is readily oxidized. This may be attested by decolorization of the solutions and by observation of oxalic acid complexes. The oxidation products are identified by I3C NMR spectroscopy as oxalic and mesoxalic acids, and experimental conditions are specified. The oxidation process requires dioxygen and photons. In parallel, the electrochemical oxidation of croconic acid is studied in aqueous media and in acetonitrile. A potential-pH diagram is drawn. 4,5-Dihydroxycyclopentenetrione 1, commonly known as "croconic" acid, H2C505, and the croconate anion [C,O,]~-have received considerable attention from both a theoretical and an experimental point of view (1-6). Croconate, like squarate or rhodizonate ions, is a member of the oxocarbon ring system, [cn0,12-, a new class of aromatic substances with planar structure containing only carbon and oxygen atoms. Both croconic and squaric acids are strong acids in aqueous solution, having pK,, values of 0.80 (7) and 0.54 (8), respectively.During the course of our investigations concerning transition metal complexes of croconic acid we attempted to prepare a manganese croconate complex. In the presence of croconic acid, 2,2'-bipyridine, and Mn(I1) salt, the complex [Mn(CloHsN2)(C204)], was unexpectedly obtained, and was structurally identified (9). This synthesis requires the oxidation of croconic acid into oxalic acid.Oxidation of croconic acid and of other polyketo compounds by molybdenum(V1) in acidic media has already been described by ; a transient 111 complex between Mo(V1) and the ionized acid was shown. 0xalic and mesoxalic acids were identified among the oxida-

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Section: Photochemical Oxidationmentioning

confidence: 99%

mentioning

confidence: 99%

A photo-oxidation of croconic acid into oxalic acid

Fabre¹,

Castan²,

Deguenon³

et al. 1995

Can. J. Chem.

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“…10,11 Here we present a study of the first two-dimensional crystallization of RA on the crystalline surfaces of gold and copper. Our starting point is the rhodizonic acid dihydrate, which we dehydrate under ultrahigh vacuum to form RA, 9RA structures. In addition, through controlling the surface chemistry and aided by first principles calculations, we were able to identify a novel surface supported metal coordinated rhodizonate species.…”

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confidence: 99%

“…The experimental treatment of the RA in this study, however, strictly followed a procedure that has been proven to dehydrate the RA. 9 Evidence for the presence of anhydrous RA is the characteristic change in color during the dehydration from colorless 8 to deep orange, 10 which is observed to be reversible after removal of the anhydrous powder from vacuum (see the Supporting Information for further images and discussion). Considering this, it is reasonable to assume that the experimental RA layers consist of the dehydrated species.…”

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confidence: 99%

Rhodizonic Acid on Noble Metals: Surface Reactivity and Coordination Chemistry

Kunkel

Hooper

Simpson

et al. 2013

J. Phys. Chem. Lett.

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A study of the two-dimensional crystallization of rhodizonic acid on the crystalline surfaces of gold and copper is presented. Rhodizonic acid, a cyclic oxocarbon related to the ferroelectric croconic acid and the antiferroelectric squaric acid, has not been synthesized in bulk crystalline form yet. Capitalizing on surface-assisted molecular selfassembly, a two-dimensional analogue to the well-known solution-based coordination chemistry, two-dimensional structures of rhodizonic acid were stabilized under ultrahigh vacuum on Au(111) and Cu(111) surfaces. Scanning tunneling microscopy, coupled with first-principles calculations, reveals that on the less reactive Au surface, extended twodimensional islands of rhodizonic acid are formed, in which the molecules interact via hydrogen bonding and dispersion forces. However, the rhodizonic acid deprotonates into rhodizonate on Cu substrates upon annealing, forming magic clusters and metal−organic coordination networks with substrate adatoms. The networks show a 2:1 distribution of rhodizonate coordinated with 3 and 6 Cu atoms, respectively. The stabilization of crystalline structures of rhodizonic acid, structures not reported before, and their transition into metal−organic networks demonstrate the potential of surface chemistry to synthesize new and potential useful organic nanomaterials.

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“…Observase que este deslocamento para o rodizonato está em campo mais fraco (204,2 ppm) que o croconato (189,3 ppm) e estes em campo mais fraco quando comparados ao esquarato (174,2 ppm). 10 Assim, conclui-se que há uma maior deslocalização de carga sobre o anel do esquarato em relação ao croconato e deste em relação ao rodizonato. Características singulares como estas fazem com que estes compostos se tornem de grande interesse quando utilizados como moléculas marcadoras espectroscopicamente.…”

Section: Introductionunclassified

Oxocarbonos, pseudo-oxocarbonos e esquaraínas

Oliveira¹,

Diniz²,

Oliveira³

2009

Quím. Nova

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Recebido em 19/11/08; aceito em 27/3/09; publicado na web em 26/8/09 OXOCARBONS, PSEUDO-OXOCARBONS AND SQUARAINES. Oxocarbons ions are cyclic compounds presenting unusual electronic and vibrational properties. These molecules anions possess a high symmetry and degree of electronic delocalization, characteristics that have been discussed in several structural and spectroscopic investigations. Compounds in which one or more of the carbonyl oxygen atoms are replaced by other atoms or groups are called pseudo-oxocarbons. Compounds formed by substitution of the carbonyl groups by nitrogen groups former a new class named squaraines. Specificity the dicyanomethylene groups are interesting because of the possibility of further extension of the electronic delocalization and a new coordination site. These molecules also present interesting coordination properties which make these systems potentially useful in crystal engineering research.Keywords: oxocarbons; pseudo-oxocarbons; squaraines. INTRODUÇÃOOxocarbonos são compostos orgânicos formados essencialmente por carbono e oxigênio, apresentam-se como diácidos em sua forma neutra e seus ânions possuem fórmula geral C n O n 2-onde n varia de 3 a 6. Os ânions croconato (n=5) e rodizonato (n=6) Os oxocarbonos apresentam características particulares muito interessantes, tais como, estruturas cíclicas planares, elevada simetria molecular, sistemas π-deslocalizados e espectros eletrônicos singulares por apresentarem o efeito Jahn-Teller. 4 Uma evidência experimental acerca da estrutura de ressonância destes compostos foi obtida por Hirata e colaboradores através da espectroscopia de absorção no infravermelho.5 Nestes estudos foi verificada a ausência da banda referente ao ν(CO) que ocorre na região ~1850-1710 cm -1. Em estudos posteriores constatou-se que a variação do tamanho do anel promove uma interessante modificação na deslocalização eletrônica do respectivo oxocarbono: quanto maior o anel menor a deslocalização eletrônica. 5Deste ponto de vista , o íon deltato é o único oxocarbono considerado realmente aromático apresentando uma maior estabilidade, devida à maior distribuição de carga, quando comparado aos demais oxocarbonos, e esta estabilidade diminui com o aumento do tamanho do anel. Os demais oxocarbonos são considerados, formalmente, não-aromáticos, porém, apresentando a elevada conjugação eletrônica característica.Estas espécies apresentam elevado valor de constante de dissociação, evidenciando a elevada estabilidade conseguida através da ressonância de seus respectivos ânions. Por exemplo, os valores de pK 1 e pK 2 para o íon croconato são 0,8 e 2,2, respectivamente, para o íon esquarato são 0,5 e 3,5 e para o rodizonato são 4,3 e 4,7, respectivamente. 6A elevada simetria molecular é verificada através de seus espectros eletrônicos, onde o perfil espectroscópico evidencia a presença do efeito Jahn-Teller característico destas espécies (Figura 2). O dupleto observado ocorre devido à dupla degenerescência do primeiro estado eletrônico excitado presente nestas molécul...

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¹³C‐NMR. Spectra, Structure and Reactivity of Cyclic Oxocarbons

Cited by 33 publications

References 24 publications

A photo-oxidation of croconic acid into oxalic acid

A photo-oxidation of croconic acid into oxalic acid

Rhodizonic Acid on Noble Metals: Surface Reactivity and Coordination Chemistry

Oxocarbonos, pseudo-oxocarbonos e esquaraínas

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13C‐NMR. Spectra, Structure and Reactivity of Cyclic Oxocarbons

Cited by 33 publications

References 24 publications

A photo-oxidation of croconic acid into oxalic acid

A photo-oxidation of croconic acid into oxalic acid

Rhodizonic Acid on Noble Metals: Surface Reactivity and Coordination Chemistry

Oxocarbonos, pseudo-oxocarbonos e esquaraínas

Contact Info

Product

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¹³C‐NMR. Spectra, Structure and Reactivity of Cyclic Oxocarbons