New Insight on the Investigation of the Role of Water in the Solid-State Structures of Potassium Croconate, K₂C₅O₅·2H₂O, and Its Anhydrate

Abstract

This work presents a comparative study of dihydrated and anhydrous forms of potassium croconate crystals by vibrational spectroscopy, X-ray powder diffraction, and thermogravimetry. These compounds have different colors (dihydrated is orange, and dehydrated is yellow) due to the presence of coordinated water molecules. X-ray diffraction patterns show that the unit cell of the yellow compound is smaller than that of the orange analogue, suggesting that the croconate ion layers are more closely bonded in this salt. The loss of water is reversible due to the potassium cation size which is intermediate between small (Li+ and Na+) and large (Rb+ and Cs+) alkaline metal ions. However, the hydrated compound (orange) is more stable, and with a small quantity of water the yellow compound is quickly converted to the orange compound. A diagnostic feature of the Raman spectrum for the orange (hydrated) and yellow (anhydrous) analogues is the singlet at 1240 cm(-1) in the former, assigned to a nu(CC) + delta(CCC) + nu(CO) + beta(CO) mode of E'2 symmetry, which splits in the yellow form to a doublet at 1256 and 1232 cm(-1).

Chemical behavior of croconic acid coordinated to Co(II) adsorbed on silver surface

“…One may notice that there are lesser number of bands than in the solid state phases because of the changes in the intermolecular interactions and the loss of structural arrangement. In the higher wavenumber region, CA shows bands at 1,609, 1,695, and 1,754 cm −1 , whereas CR has bands at 1,587, 1,609, and 1,719 cm −1 , all assigned to different CO stretching modes . The absence of any shoulder in the band at 1,719 cm −1 in the CR Raman spectrum can be rationalized by the equivalence of the local environment around each oxygen atoms in solution, different from the observed in the solid state.…”

“…The Raman spectrum of CA shows more bands than CR, because the latter presents a higher symmetry due to the delocalized π‐electrons. The assignments of the Raman bands of both CA and CR have been previously studied thoroughly in the literature . Notably, the Raman spectrum of CA shows, in the higher wavenumber region, two bands at 1,722 and 1,757 cm −1 , whereas CR has a band at 1,723 cm −1 and a shoulder at 1,719 cm −1 , all assigned to CO stretching modes.…”

“…In the low wavenumber region of both CA and CR Raman spectra, fewer differences are observed in terms of number, position, and relative intensity of the bands. Two bands are present in CR spectrum at 558 and 637 cm −1 , assigned to ring bending and ring breathing modes, respectively . The corresponding bands in the Raman spectrum of CA are observed at 552 and 630 cm −1 .…”

Squaraines: Crystal Structures and Spectroscopic Analysis of Hydrated and Anhydrous Forms of Squaric Acid-Isoniazid Species

“…In other words, Braga and co-workers presented a correlation between cation size and the kind of packing in the solid state. In another investigation, Da Silva et al performed a similar study involving heating potassium croconate K 2 C 5 O 5 ·2H 2 O salt, where it could be observed from the XRD pattern of the hydrated (orange) and anhydrous (yellow) species that the most intense peaks occurred at 2θ = 11.45 and 24.5°. These peaks represent the d hkl value of 7.72 and 3.63 Å, respectively, and are indicative of a small interplanar distance for the dehydrated structure, consequently related to a possible reduction in the oxocarbon ring distance in the packing, which was also observed in the present study by single crystal diffraction.…”

Hydration‐Facilitated Fine‐Tuning of the AIE Amphiphile Color and Application as Erasable Materials with Hot/Cold Dual Writing Modes

“…Many inorganic crystals in nature contain a certain amount of coordinating water, which induces energy level splitting of the central metal ions. This results in absorption of visible light of certain wavelength, so that the crystal displays the complementary color . Well‐known examples are CuSO 4 ⋅5 H 2 O and CoCl 2 ⋅6 H 2 O.…”