The ditopic molecule 3-(1,3,5-trimethyl-4-1H -pyrazolyl)acetylacetone (HacacMePz) combines an acetylacetone group suitable for deprotonation and O,O' coordination to a Pearson-hard cation with a softer N-donor site. Both binding modes were employed individually: The pyrazolyl moiety was coordinated to Zn II , Cd II , Hg II and Ag I , and with trivalent iron the tris-chelating O,O' complex [Fe(acacMePz) 3 ] was isolated. The Cu II derivative shows shorter O,O' chelation and N coordination in the more distant Jahn-Teller sites and exists in two alternative crystal forms, namely as a tetranuclear discrete complex and as a chain polymer. The dierent Pearson hardnesses of the coordination sites of acacMePz − allow for the design of well-ordered mixed-metal solids. Selective complexation to a hard and a soft cation was achieved in coordination polymers combining hard Fe III and softer Hg II or Ag I . Even slight dierences in Pearson hardness based on dierent oxidation states of the same cation imply sucient selectivity, as shown by the successful synthesis of a mixed-valent Cu II /Cu I chain polymer. A 1 synopsis of all structurally characterized compounds conrms that HacacMePz represents a bridging ligand with restricted conformational freedom. No full rotation about the single bond between the pyrazolyl and acetylacetone fragments occurs, and dihedral angles between these moieties are limited to values of 90°± 17°.
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.
The heteroditopic molecule HacacMePz combines a Pearson hard acetylacetone donor site with a softer trimethylpyrazole and shows site selectivity towards the coinage metal cations. The coordination of the N donor function was achieved towards AgI and AuI, leading to the salt [Ag(HacacMePz)2]PF6 (1) and the neutral complex [AuCl(HacacMePz)] (2). In either case, linear coordination about the coinage metal cation is observed. Interestingly, both complexes crystallize in space group Pbca with similar cell parameters. The two solids do not qualify as isostructural, albeit being closely related in real and reciprocal space. To probe the ligand’s ability for the envisaged synthesis of bimetallic coordination polymers, the mixed-metal CuII/AuI complex [Cu(acacMePzAuCl)2] (3) was obtained. In this mixed-metal oligomer, the central CuII cation adopts a square planar coordination environment with two O,O′-coordinated acacMePz− ligands, whose softer N donor sites are saturated with a AuCl moiety.
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