doi:10.1039/d5dt02386fengPolo, AlvaroGarcía-Orduña, PilarEcheverría, JorgeSanz Miguel, Pablo J.Unveiling n → π* interactions: convergence of quantum crystallography and computational insightsART-2026-148062We report the identification and characterization of a n → π* interaction between halide anions and a cationic purine nucleobase. Through a combined quantum crystallographic and computational approach, we demonstrate that perpendicular anion⋯(sp2)carbon contacts occur consistently at the C2 position of the purine nucleobase, with geometries and energies comparable to hydrogen bonds. High-resolution X-ray charge density analysis of 2[Br]·H2O confirms the existence of a bond path and an electron density depletion on C2, supporting a charge-transfer interaction. Complementary theoretical studies reveal a lone pair-to-π* orbital delocalization mechanism, with second-order NBO energies up to 6 kcal mol−1. The interaction persists with various anions, hydration levels, and C2 substitutions, highlighting its robustness and potential relevance in supramolecular chemistry. This study provides the experimental validation of an n → π* contact, supported by topological and electrostatic descriptors.2026http://zaguan.unizar.es/record/16864310.1039/d5dt02386fhttp://zaguan.unizar.es/record/168643oai:zaguan.unizar.es:168643info:eu-repo/grantAgreement/ES/DGA/E05-23Rinfo:eu-repo/grantAgreement/ES/DGA/E42-23Rinfo:eu-repo/grantAgreement/ES/MCIU-AEI-FEDER/PID2021-122406NB-I00Dalton Transactions (2026), [8 p.]All rights reservedhttp://www.europeana.eu/rights/rr-f/info:eu-repo/semantics/embargoedAccess