Pressure-induced spin transition and site-selective metallization in CoCl 2

The interplay between spin states and metallization in compressed CoCl 2 is investigated by combining diffraction, resistivity and spectroscopy techniques under high-pressure conditions and ab-initio calculations. A pressure-induced metallization along with a Co 2+ high-spin (S = 3/2) to low-spin (S = 1/2) crossover transition is observed at high pressure near 70 GPa. This metallization process, which is associated with the p - d charge-transfer band gap closure, maintains the localization of 3 d electrons around Co 2+ , demonstrating that metallization and localized Co 2+ -3 d low-spin magnetism can coexist prior to the full 3 d -electron delocalization (Mott-Hubbard d-d breakdown) at pressures greater than 180 GPa.