Sara Busi

Novel one-pot synthesis of quaternary ammonium halides: new route to ionic liquids

Treatment of an amide with an alkyl or substituted alkyl halide in the presence of a weak base in a one-pot reaction leads to crystalline quaternary ammonium halides with reasonable chemical yields; some of the compounds show low melting points and a liquid range of over 50–100 °C before decomposition.

The role of cation⋯π interactions in capsule formation: co-crystals of resorcinarenes and alkyl ammonium salts

An unprecented dimeric capsular assembly of a tetramethylated C-hexyl resorcinarene and an expected one from unsubstituted C-butyl resorcinarene with tetramethylammonium cation are described. Surprisingly tetramethylated C-hexyl resorcinarene, with no apparent possibility for intra-capsular hydrogen bonds, forms a capsule which is held together solely by the cation⋯π interactions and the complementary geometry of the spherical guest cation and the concave resorcinarene host. The C-butyl resorcinarene capsule, as in the case of dimeric resorcinarene capsules reported earlier, is mediated viasolvent molecules and intra-capsular hydrogen bonds. We also report here two co-crystals of C-methyl resorcinarene and one of C-(3-hydroxy)propyl resorcinarene with R2,R′2-type of alkyl ammonium halide salts. These structures manifest the difficulty of structure control and prediction due to competing and multiple interactions in the crystalline state. The design of the resorcinarene-based host–guest system so as to enable prediction or inducement of a specific crystal packing or structural arrangement of host and guest, is very difficult, if not impossible due to the cameleon nature of resorcinarenes in their ability to form weak interactions.

A linear Fe–O–Fe unit in bis­(dibenzyl­dimethyl­ammonium) μ-oxo-bis­[tribromo­ferrate(III)]

The title compound, (C16H20N)2[Fe2Br6O], crystallizes with one dibenzyldimethylammonium cation and one half of a mu-oxo-bis[tribromoferrate(III)] anion in the asymmetric unit. The bridging oxo group is situated on an inversion centre, resulting in a linear conformation for the Fe-O-Fe unit. The iron(III) cations have tetrahedral geometry, with bond angles in the range 106.8 (1)-112.2 (1) degrees . The ion pairs are held together by Coulombic forces and C-H...Br hydrogen bonds. Each Br- anion forms one hydrogen bond. No C-H...O hydrogen bonds are found between the O atom in the Fe-O-Fe unit and surrounding counter-cations, consistent with the linear configuration of the Fe-O-Fe unit.

Crystal Structures and Thermal Behavior of Bis(dibenzyldimethylammonium) Tetrabromometallates(II) [M = Mn(II), Co(II) and Zn(II)] and Their Solvates

Six new A2MBr4 structures [A = dibenzyldimethylammonium cation,M = Mn(II), Co(II) or Zn(II)] were crystallized with or without solvent molecules from acetonitrile, methanol and/or aqueous solutions. The isomorphous compounds [(Bz2Me2N)2][MnBr4]·CH3CN·H2O (1) and [(Bz2Me2N)2]-[ZnBr4]·CH3CN·H2O (4) crystallize in the triclinic space group P1̄ from acetonitrile solutions. The solvent molecules participate in the hydrogen bonding network inside the crystal structure. [(Bz2Me2N)2][CoBr4]·0.5CH3CN (2) crystallizes from an acetonitrile solution in the monoclinic space group P21/c. The solvent molecules fill the voids of the crystal structure. Compound 2 is isostructural with the previously reported compounds [(Bz2Me2N)2][MCl4]·0.5CH3CN with M = Mn(II), Co(II), Ni(II), Cu(II) or Zn(II). [(Bz2Me2N)2][CoBr4] (3) and [(Bz2Me2N)2][ZnBr4] (5a) crystallize from a methanol solution in the monoclinic space group P21/c without solvents. A polymorph of compound 5a, [(Bz2Me2N)2][ZnBr4] (5b), was crystallized from aqueous solution in the monoclinic space group P21/c. The packing of the components of the two polymorphs differs clearly. One cation of 5a appears in the W-conformation whereas the other cation of 5a and both cations of 5b appear in twisted conformations. In addition to the ionic interactions between the ion pairs, the packing of the compounds is stabilized by hydrogen bonds and weak intermolecular π-π interactions in all cases. The compounds melt around 200 °C and decompose mainly in two steps just above the melting point. Slow evaporation of solvents is observed both in the TG and DSC diagrams of the solvates (1, 2 and 4) below 100 °C.

Crystal Structures and Thermal Behavior of Isostructural Bis(dibenzyldimethylammonium) Tetrachlorometallate (M = Mn(II), Co(II), Ni(II) and Zn(II)) Solvates Crystallized from Acetonitrile and/or Methanol Solutions

Five isostructural bis(dibenzyldimethylammonium) tetrachlorometallate solvate complexes [M = Mn(II), Co(II), Ni(II) or Zn(II)] were crystallized from acetonitrile and/or methanol solutions. The crystal structures are compared to those of the analogous, isostructural copper compounds (X = Cl or Br) reported earlier. The complexes crystallize in the monoclinic space group P21/n with Z = 4, and unit cell dimensions of a ≈ 14.1, b ≈ 16.1, c ≈ 15.7 °A and β ≈ 108 - 109°. The asymmetric unit of these compounds contains one MCl42− anion, two Bz2Me2N+ cations in theW-conformation and one half of a disordered solvent molecule (acetonitrile or methanol). The geometry of the MCl42− anion is close to tetrahedral, whereas the analogous copper anions appeared in distorted tetrahedral geometries with trans angles of 124.4° for X = Cl and 123.6° for X = Br. In addition to the ionic interactions between the cations and the anions, the components are connected by weak C-H· · · Cl− bonds. As a distinction between the two crystallographically independent cations in the asymmetric unit, one type of independent cations form long chains via weak edge to face π-π interactions along the crystallographic b axis, whereas the other type of cations are not tied together by such weak π-π interactions. The coordination around the N atoms is also nearly tetrahedral, and neither static nor dynamic disorder of the Bz2Me2N+ cations can be observed. The complexes are thermally stable and melt close to the decomposition temperatures in the range 170 - 205 °C.