Propriedades estruturais, espectroscópicas e térmicas do sal de Tutton Rb2Co(SO4)2(H2O)6: uma abordagem experimental e teórica visando aplicações em dispositivos ópticos

Abstract

This work investigates the structural, spectroscopic, thermal, and optical properties of the Rb2Co(SO4)2(H2O)6 crystal, a Tutton salt with potential application in selective optical devices. The material was synthesized by slow solvent evaporation and

characterized by powder X-ray diffraction (PXRD) with Rietveld refinement, Fourier- transform infrared (FT-IR) and Raman spectroscopies, thermogravimetric and

differential scanning calorimetry (TG-DSC) analyses, and ultraviolet–visible–near infrared (UV-Vis-NIR) spectroscopy. The monoclinic crystal structure, belonging to the P21/a space group, was confirmed, with lattice parameters consistent with literature data. The analysis of intermolecular interactions, via Hirshfeld surfaces and calculations of crystal voids, revealed a dense lattice packing, predominantly governed by O···H/H···O hydrogen bonds, O···Co/Co···O coordination interactions, and Rb···O/O···Rb electrostatic interactions. Periodic calculations based on Density Functional Theory (DFT) indicated an electronic band gap of approximately 3.0 eV, mainly associated with the contributions of the Co2+ ion's d orbitals. Vibrational characterization allowed for the suitable assignment of Raman and FT-IR modes based on the structural units [Co(H2O)6] 2+, [SO4] 2- , and Rb+

. TG-DSC analyses revealed a dehydration event at approximately 111 °C, with the associated enthalpy for the dehydration process. The optical study showed absorption bands in the UV region associated with ligand-to-metal charge transfer transitions and bands in the Vis region attributed to d-d electronic transitions of the Co2+ ion, evidencing the Jahn-Teller effect. The observed absorption and transmittance windows indicate the material's intrinsic spectral selectivity, reinforcing its potential for applications in optical filters and selective photonic systems.