Pressure-Driven Symmetry-Preserving Phase Transitions in Co(IO₃)₂

High-pressure synchrotron X-ray diffraction studies of cobalt iodate, Co(IO3)2, reveal a counterintuitive pressure-induced expansion along certain crystallographic directions. Raman and infrared spectroscopy, combined with density-functional theory calculations, that increasing pressure, it becomes energetically favorable for I–O bonds to increase in length over the full range pressure studied up 28 GPa. This phenomenon is driven by high-pressure behavior iodate ion lone electron pairs. Two isosymmetric monoclinic–monoclinic phase transitions are observed at around 3.0 9.0 GPa, which characterized oxygen coordination iodine atoms probable formation metavalent bonds. Pressure–volume equations state presented, as well detailed discussion dependences Raman- infrared-active modes, clarifies previous inconsistencies literature.