PRESSURE-INDUCED ELECTRON-TRANSFER IN QUASI-MOLECULAR SOLIDS

A combination of Raman scattering and synchrotron X-ray powder diffrac tion on Group-V metal triiodides (XI(3), X = As, Sb, Bi) has revealed a continuous isostructural transition from a molecular solid to a two- dimensional layered crystal under high pressure. The loss of molecular identity proceeds by gradual pressure-induced electron transfer from intramolecular to intermolecular bonds and suppression of sp(3) hybrid isation. Initial pressure increase has the effect of destroying molecu lar units while continued compression enhances intralayer cohesion. Th ese two effects give rise to a non-monotonic pressure variation of the X-I bond-stretching frequency.