Competing Patterns of Weak Directional Forces in Pressure-Frozen CH₂ClI and CH₂I₂

Isostructural relations and phase transitions of dihalomethanes have been rationalized by the competing patterns of CH···halogen hydrogen bonds and halogen···halogen interactions, the common weak directional interactions in soft organic matter. Pressure-frozen chloroiodomethane, CH2ClI, at 295 K and 0.72 GPa forms centrosymmetric phase III, which at ca. 400 K and 1.6 GPa disproportionates into CH2Cl2 and CH2I2. The directional character of intermolecular contacts between halogen atoms results from the characteristic anisotropic charge distribution on molecular surface.二卤代甲烷（dihalomethanes）的同构关系与相变过程，可通过CH···卤素氢键（CH···halogen hydrogen bonds）与卤素-卤素相互作用（halogen···halogen interactions）这两类软有机物质（soft organic matter）中常见的弱定向相互作用的竞争模式予以合理解释。在295 K、0.72 GPa条件下加压冷冻的氯碘甲烷（CH₂ClI），可形成中心对称相III（centrosymmetric phase III）；该相在约400 K、1.6 GPa时会发生歧化反应，分解为二氯甲烷（CH₂Cl₂）与二碘甲烷（CH₂I₂）。卤素原子间分子间接触（intermolecular contacts）的定向特征，源于分子表面特征性的各向异性电荷分布（anisotropic charge distribution）。