Polynuclear Superhalogen Anions with Heterovalent Central Atoms

This study explores a novel class of polynuclear superhalogen anions featuring heterovalent central atoms from groups 13 (B, Al) and 15 (P, As). The investigated species follow a modified general formula, (<b>X</b><i>_n</i><b>Y</b><i>_n_'</i>F_{{(3<i>n</i>+5<i>n</i>}<i>_'</i>_)+1})^- where <b>X</b> = B and/or Al, <b>Y</b> = P and/or As, and <i>n</i> + <i>n'</i> = 2-4. Low-energy isomers were identified using the Coalescence Kick method and subsequently optimized at the MP2/aug-cc-pVDZ level of theory. Electronic stability was assessed via the outer valence Green's function (OVGF) approach with the same aug-cc-pVDZ basis set. All examined anions exhibit exceptional electronic stability, with vertical electron detachment energies (VDEs) ranging from 10.70 to 12.37 eV, significantly exceeding the superhalogen threshold of 3.65 eV. Thermodynamic analyses indicate that aluminum atoms play a crucial role in stabilizing larger clusters by acting as a structural "glue", thereby suppressing fragmentation through the loss of neutral <b>X</b>F₃ or <b>Y</b>F₅ units. In contrast, larger non-metallic analogs show an increased propensity toward dissociation. The potential of the heterovalent polynuclear superhalogen anions as weakly coordinating anions (WCAs) was further evaluated through molecular electrostatic potential (ESP) analysis. The results demonstrate that combining different central atoms within boron-based frameworks leads to a more homogeneous charge distribution, enhancing weakly coordinating behavior.