Spring‐Loaded p‐Block Ions: Homodesmotic Ring Strain Energy Benchmarks for Charged Three‐Membered Rings

Ring strain energy (RSE) is central to the stability and ring‐opening chemistry of three‐membered rings (3MRs), yet reliable benchmarks for ionic p‐block 3MRs remain scarce. Here, we establish a unified homodesmotic protocol for charged saturated 3MRs: monocationic pnictogeniranium, chalcogeniranium and halonium ions, and monoanionic trieliranides bearing H, F, or Me ligands. A three‐tier workflow, from GFN2‐xTB screening to DLPNO‐CCSD(T)/def2‐QZVPP refinement, is used to compare counter‐ion‐free reactions, Coulomb‐corrected charge‐separated products and explicit ion pairs with SbF 6 − or Cs + . Benchmarking shows that naked‐ion C─C cleavage, or the average of naked‐ion C─C and C─El cleavages where appropriate, gives the most transferable RSE scale while avoiding artifacts from ion pairing. Cationic 3MRs are generally more strained than their neutral analogs, whereas trieliranides show stronger substituent control, with fluorination markedly increasing RSE. The heaviest pnictogeniranium cations (As, Sb, Bi) are best described as pseudocyclic, nonclassical multicentre C 2 Pn frameworks lacking an RCP and displaying Dewar–Chatt–Duncanson‐type structures. Periodic trends are rationalized through lone‐pair‐driven hybridization changes and charge‐dependent bonding. Additive atom and bond strain contributions are reported to enable rapid estimation of RSE in charged p‐block 3MRs.