The structure and spectra of squaric acid

Thackeray, D. P. C.; Shirley, Robin; Stace, B. C.

doi:10.1016/0038-1098(78)90901-8

Cited by 9 publications

(5 citation statements)

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“…The experimental Raman spectrum of the squaric acid has been obtained in many occasions and may be found in several published articles. − For example, this spectrum was recorded at 309 K by Baglin and Rose in 1970 with an estimated resolution of ±4 cm –1 . Similarly, Nakashima and Balkanski recorded the Raman spectrum of squaric acid at 77 K in 1976 with an improved resolution of about ±2 cm –1 .…”

Section: Resultsmentioning

confidence: 99%

“…While these important materials have been studied at length experimentally, their characterization was relatively poor. One of the most surprising features of this study is that the characterization of their Raman spectra, being very accurately recorded and published in a large number of excellent spectroscopic studies, [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] was not reliable. This is due to the use of the empirical method of assignment as the only source of information, surely for lack of relevant theoretical solid-state calculations.…”

Section: Discussionmentioning

confidence: 99%

“…6 The second one is their fundamental thermodynamic properties and the third one is their ultraviolet-visible (UV-Vis) optical spectra and properties. Finally, although the Raman spectra of these materials have been recorded experimentally in many previous works, [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] the band assignments were founded on empirical arguments only. The results obtained in the present theoretical solid-state calculations of the deltic, squaric and croconic acids ( = 3, 4 and 5, respectively), pointed out to significant problems in their assignment.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, the Raman spectra of these materials were reassigned. Of course, this feature is not a critique to the excellent spectroscopic works performed so far [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] for these materials but to the empirical method of assignment which is too rough to provide the correct spectral interpretations in many occasions. [24][25] The extrapolation of spectroscopic data from gas phase molecule to solid state materials is a very crude approximation indeed.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, the Raman spectra of these materials were reassigned. Of course, this feature is not a critique to the excellent spectroscopic works performed so far − for these materials but to the empirical method of assignment, which is too rough to provide the correct spectral interpretations in many occasions. , The extrapolation of spectroscopic data from gas-phase molecules to solid-state materials is a very crude approximation indeed. Likewise, the use of normal-coordinate treatments based on approximate force-field methods ,,,,, may lead to significant errors in the calculated spectra of solid materials and their assignment.…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamic, Raman Spectroscopic, and UV–Visible Optical Characterization of the Deltic, Squaric, and Croconic Cyclic Oxocarbon Acids

Colmenero

Escribano

2019

J. Phys. Chem. A

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A precise and complete thermodynamic, Raman spectroscopic and ultraviolet-visible optical characterization of the deltic, squaric and croconic cyclic oxocarbon acids is obtained using theoretical solid-state methods employing very demanding calculation parameters. The computed fundamental thermodynamic properties include the isobaric specific heat, the entropy, the enthalpy and the Gibbs free energy as a function of temperature. The calculated specific heats at 298.15 K of the deltic, squaric and croconic acids are 89.7, 111.2 and 133.2 J • mol −1 • K −1 , respectively, and the corresponding entropies are 98.3, 117.3 and 136.5 J • mol −1 • K −1 . The only value of these properties known from experimental measurements is the specific heat of the squaric acid which differs from the computed value at 315 K by about 4.9%. The calculated values of the thermodynamic properties are then used to determine the thermodynamic properties of formation of these materials in terms of the elements. As an application of the calculated thermodynamic properties of formation, the Gibbs free energies of reaction and associated reaction constants are evaluated for the reactions of thermal decomposition and complete combustion of the squaric and croconic acids and the reaction of interconversion between them. The only available experimental values of these properties, namely the enthalpies of combustion of squaric and croconic acids at room temperature, are reproduced theoretically with high accuracy. The Raman spectra of these materials are also computed using Density Functional Perturbation Theory. The analysis of the theoretical Raman spectra of these materials points out to significant differences with respect to their usual empirical assignment. Therefore, the Raman spectra of these materials is fully reassigned. Finally, the ultraviolet-visible (UV-Vis) optical properties of the deltic, squaric and croconic acids are computed. The UV-Vis absorption spectrum of the croconic acid in the spectral region 225-425 nm and the UV absorption spectrum of the squaric acid in the region 200-350 nm which had previously been measured experimentally are well reproduced. The corresponding spectrum for the deltic acid and the reflectivity, optical conductivity, dielectric, refractive index and loss optical functions of the three materials, which had never been published as far as we know, are reported as a function of the wavelength of incident radiation in the range 200-750 nm. The origin of the peaks in the absorption spectra which had not been analyzed so far is unveiled here by examining the inter-band electronic transitions in these materials.their reactions of complete combustion:and the reaction of conversion between them in the presence of carbon monoxide: (E) H 2 C 4 O 4 (cr) + CO(g) → H 2 C 5 O 5 (cr) as a function of temperature. The thermodynamic parameters of organic compounds are extraordinarily important not only in

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermodynamic, Raman Spectroscopic, and UV–Visible Optical Characterization of the Deltic, Squaric, and Croconic Cyclic Oxocarbon Acids

Colmenero

Escribano

2019

J. Phys. Chem. A

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Raman and infrared spectra in organic layer crystals of squaric acid

Nakashima

Aziza

Postollec

et al. 1979

Physica Status Solidi (b)

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The Raman spectra of squaric acid and its deuterated derivative are measured for temperatures from 77 to 450 K covering both ordered and disordered phases. Infrared absorption spectra are investigated for thin films of the single crystals and compared with the Raman spectra. It is found that the vibrational Davydov splitting due to the interlayer interaction is large for the external modes, while i t is small for the internal modes of the squaric molecule. This behavior is explained by the model that the interlayer interaction acts between the hydrogen bonds of adjacent layers and is localized in the region near the hydrogen bonds. The temperature dependence of the frequencies and the linewidths is discussed in relation to the phase transition mechanism.Les spectres Raman de I'acide carre et de son dkrivk deuterie ont BtB mesurks Q des tempkratures comprises entre 77 e t 450 K couvrant & la fois les phases ordonnkes e t dbsordonnkes. Les spectres d'absorption infrarouges ont Btk Btudiks sur des couches minces monocristallines e t compares avec les spectres Raman. On a constate que le dkdoublement vibrationnel de Davydov du^ a l'intkraction intercouche est large pour les modes externes, mais petit pour les modes internes de la molkcule carr6e. Ce comportement est expliquk par le modde: l'inthraction intercouche agit entre Ies liaisons hydrogene des couches adjacentes e t est localiske dans la region pres des liaisons hydrog h e . La dependance de la tempkrature, des frkquences e t des Iargeurs de raies est discutke en relation avec le mkcanisme de la transition de phase.

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A crystal-dynamical approach to squaric acid

Bougeard

1984

Chemical Physics

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The structure and spectra of squaric acid

Cited by 9 publications

References 4 publications

Thermodynamic, Raman Spectroscopic, and UV–Visible Optical Characterization of the Deltic, Squaric, and Croconic Cyclic Oxocarbon Acids

Thermodynamic, Raman Spectroscopic, and UV–Visible Optical Characterization of the Deltic, Squaric, and Croconic Cyclic Oxocarbon Acids

Raman and infrared spectra in organic layer crystals of squaric acid

A crystal-dynamical approach to squaric acid

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