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 (C11H16N2O2, HacacMePz) was protonated with HX (X   = Cl or Br) to afford the hydrohalides, C11H17N2O2+ · X − or H2acacMePz+ · 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 C11H17N2O2+ · Br − · 0.5C6F4I2 · H2O or (H2acacMePz+ · Br − )2 · (H2O)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\overline{2}) plane. Assisted by their negative charge, halide anions represent particularly good nucleophiles towards XB donors.

Source: Acta Crystallographica Section C - May 9, 2022 Category: Chemistry Authors: van Terwingen, S. Ebel, B. Wang, R. Englert, U. Tags: crystal engineering halogen bonds hydrogen bonds QTAIM electron density research papers Source Type: research