Weaving a 2D net of hydrogen and halogen bonds: cocrystal of a pyrazolium bromide with tetrafluorodiiodobenzene.

Hydrohalides of Lewis bases may act as halogen bond (XB) acceptors and combine two directional interactions, namely, hydrogen bonds (HB) and XBs in the same solid. 3-(1,3,5-Trimethyl-1H-pyrazol-4-yl)acetylacetone (C 11 H 16 N 2 O 2 , HacacMePz) was protonated with HX (X = Cl or Br) to afford the hydrohalides, C 11 H 17 N 2 O 2 + ·X - or H 2 acacMePz + ·X - (1, X = Cl; 2, X = Br). Hydrohalides 1 and 2 are isomorphous and adopt a classical dipole packing. Consistent with the observation for most β-diketones, the enol form with an intramolecular HB is observed. Additional noteworthy interactions are HBs of the protonated pyrazolium towards the X - anion at donor-acceptor distances of 2.9671 (17) Å for 1 and 3.159 (4) Å for 2. Cocrystallization of hydrobromide 2 with the XB donor tetrafluorodiiodobenzene (TFDIB) leads to the adduct C 11 H 17 N 2 O 2 + ·Br - ·0.5C 6 F 4 I 2 ·H 2 O or (H 2 acacMePz + ·Br - ) 2 ·(H 2 O) 2 ·TFDIB (3), in which the XB donor TFDIB is situated on a crystallographic centre of inversion. Classical HBs link organic cations, water molecules and Br - anions into chains along [010]. Almost orthogonal to this interaction, XBs with Br...I = 3.2956 (4) Å connect neighbouring chains along [102] into two-dimensional sheets in the (10-2) plane. Assisted by their negative charge, halide anions represent particularly good nucleophiles towards XB donors.