Hydrogen-Bonded and Halogen-Bonded: Orthogonal Interactions for the Chloride Anion of a Pyrazolium Salt

In the hydrochloride of a pyrazolyl-substituted acetylacetone, the chloride anion is hydrogen-bonded to the protonated pyrazolyl moiety. Equimolar co-crystallization with tetrafluorodiiodobenzene (TFDIB) leads to a supramolecular aggregate in which TFDIB is situated on a crystallographic center of inversion. The iodine atom in the asymmetric unit acts as halogen bond donor, and the chloride acceptor approaches the [Formula: see text]-hole of this TFDIB iodine subtending an almost linear halogen bond, with Cl···I = [Formula: see text] Å and Cl···I–C = 179.32(6)°. This contact is roughly orthogonal to the N–H···Cl hydrogen bond. An analysis of the electron density according to Bader’s Quantum Theory of Atoms in Molecules confirms bond critical points (bcps) for both short contacts, with [Formula: see text] = 0.129 for the halogen and [Formula: see text] e [Formula: see text] for the hydrogen bond. Our halogen-bonded adduct represents the prototype for a future class of co-crystals with tunable electron density distribution about the [Formula: see text]-hole contact.