Properties and Perspectives of Rb<sub>2</sub>Co(SO<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub> Tutton Crystal: A Combined Experimental-Theoretical Analysis.

Abstract

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 <i>P</i>2₁/<i>a</i>-space group in the monoclinic system (unit cell parameters <i>a</i> = 9.204(9) Å, <i>b</i> = 12.467(2) Å, <i>c</i> = 6.246(3) Å, β = 106.02(5)°, and <i>V</i> = 688.93(4) ų). 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 (Δ<i>H</i> = 301.15 kJ/mol). While electronic band structure indicates an electronic bandgap of 3.00 eV, dominated by Co²⁺ <i>d</i>-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.