Properties and Perspectives of Rb₂Co(SO₄)₂(H₂O)₆ Tutton Crystal: A Combined Experimental-Theoretical Analysis

This paper presents a comprehensive investigation of a Tutton crystal, rubidium cobalt sulfate hexahydrate Rb2Co(SO4)2(H2O)6, detailing its synthesis and characterizing its structural (PXRD), vibrational (FT-IR and Raman), thermal (TG and DSC), and optical (UV-vis-NIR) properties. Complementary, calculations using density functional theory (DFT) were implemented to estimate electronic band structure and assign optical phonon modes identified through FT-IR and Raman spectra. The material was prepared by the slow solvent evaporation method and crystallized, having P21/a-space group in the monoclinic system (unit cell parameters a = 9.204(9) Å, b = 12.467(2) Å, c = 6.246(3) Å, β = 106.02(5)°, and V = 688.93(4) Å3). Hirshfeld surface analysis and void calculations revealed a densely packed structure stabilized by strong O···H/H···O hydrogen bonds, followed by O···Co/Co···O contacts, with a void volume of only 1.4%. Thermograms show a full dehydration at ≈ 384 K (ΔH = 301.15 kJ/mol). While electronic band structure indicates an electronic bandgap of 3.00 eV, dominated by Co2+ d-orbital contributions, the optical measurements display an optical bandgap of ≈ 4.13 eV, attributed to ligand-to-metal charge transfer bands involving electron donation from the nonbonding orbitals of H2O to the Co2+ orbitals. The optical absorbance (200–300 nm) transmittance (300–420 nm/580–1100 nm) windows underscore the potential of Rb2Co(SO4)2(H2O)6 crystal.