Interactions in inorganic molecular crystals. Electronic spectra of ReF6 pure and mixed crystals

Electronic absorption spectra of ReF6(5d1) are obtained for the pure crystal and UF6, MoF6, and WF6 mixed crystals. The observed transition arises from an intraconfigurational t2g→t2g promotion characterized Γ7g←Γ8g in 0h symmetry. The pure crystal is predicted to undergo a magnetic phase transition below ∼1.5 K. Pair spectra, two-molecule transitions, the ground state Jahn–Teller effect, linewidths, and vibrational assignments are discussed. The major mechanism for pair coupling and magnetic ordering is identified as superexchange through low lying delocalized charge transfer bands. These interactions are qualitatively discussed and energy localizing and delocalizing interactions are separated.