Structural, Optical, and Magnetic Properties of Ultramarine Pigments: A DFT Insight

Abstract

The ultramarine pigments are among the most widely used coloring materials since the antiquity till present times. Despite many experimental studies, the characterization of ultramarines is still incomplete. In this work, we reported for the first time the density functional theory results obtained for realistic periodic and large cluster models of ultramarines with blue S 3 − and yellow S 2 − chromophores. Periodic calculations provided insight into S n − siting inside aluminosilicate cages, normally not resolved well in experimental structural data. All electron calculations performed on large cluster models showed that the optical properties of S 3 − ions depend little on their orientation within cavities, unless strong distortion from free S 3 − ion C 2v symmetry is enforced by the lattice. No magnetic coupling between S 3 − species occupying adjacent cages was found. Upon the present results, observed differences in the averaging of electron resonance signals should be rather ascribed to different S 3 − dynamical effects. Though the quantitative computational treatment of S 2 − systems is more challenging because of near orbital degeneracy, the qualitative results show that the electronic structure and spectroscopic properties of embedded S 2 − radicals are more sensitive to the environment than in the case of S 3 − species.

Reviving Alexander Calder’s Man-Eater with Pennants: A Technical Examination of the Original Paint Palette

“…The broad absorption of green-yellow-orange visible light of this radical, centered around 600 nm, gives the pigment its signature blue color. This energy corresponds to an electronic transition between two singly occupied molecular orbitals [35]. Ultramarine was identified through Raman spectroscopy (Figure 7) by the S 3 − radical symmetric stretch at 540 cm −1 [36].…”

1-Ethyl-3-methylimidazolium Acetate as a Reactive Solvent for Elemental Sulfur and Poly(sulfur nitride)

“…Raulin et al reported g -values (2.054, 2.041, and 2.005) at 30 K for [S 3 ] •– of different UM pigments. DFT studies on UMs also returned a rhombic g-tensor (2.002, 2.056, 2.040) for trisulfide radical …”

“…The presence of two radical components with different dynamics (mobilities) could also explain the broad line width of observed EPR spectra at room temperature. Since there is no crystal structure available for the trisulfide radical, theoretical studies suggest a C 2 v symmetry. , Comparing the obtained results in this study with those in the literature, one might conclude that the symmetry of the trisulfide radical in the IL is preserved.…”

Sapozhnikovite, Na8(Al6Si6O24)(HS)2, a new sodalite-group mineral from the Lovozero alkaline massif, Kola Peninsula

“…Analogous signals of S 2 •– have also been observed in the ESR spectra of other sodalite-group minerals (Chukanov et al , 2020b) and ultramarine analogues prepared from zeolites (Kowalak et al ., 2007). However, S 2 •– spectra can be undetectably broadened by radical dynamics and should be very environmentally dependent due to the varying interaction between split π* states of S 2 •– in different local environments (Rejmak, 2018). In alkali halides S 2 •– radicals have been well-studied and g components demonstrate strong anisotropy and variability (Vannotti and Morton, 1967; Callens et al , 1989).…”