: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Tetrathiafulvalenes, oligoacenenes, and their buckminsterfullerene derivatives: the brick and mortar of organic electronics.

A halogen bond is a highly directional, electrostatically-driven noncovalent interaction between a region of positive electrostatic potential on the outer side of the halogen X in a molecule R–X and a negative site B, such as a lone pair of a Lewis base or the π-electrons of an unsaturated system. The positive region on X corresponds to the electronically-depleted outer lobe of the half-filled p-type orbital of X that is involved in forming the covalent bond to R. This depletion is labeled a σ-hole. The resulting positive electrostatic potential is along the extension of the R–X bond, which accounts for the directionality of halogen bonding. Positive σ-holes can also be found on covalently-bonded Group IV–VI atoms, which can similarly interact electrostatically with negative sites. Since positive σ-holes often exist in conjunction with negative potentials on other portions of the atom's surface, such atoms can interact electrostatically with both nucleophiles and electrophiles, as has been observed in surveys of crystallographic structures. Experimental as well as computational studies indicate that halogen and other σ-hole interactions can be competitive with hydrogen bonding, which itself can be viewed as a subset of σ-hole bonding.

Halogen bonding: an electrostatically-driven highly directional noncovalent interaction

Conversion constants for redox potentials measured versus different reference electrodes in acetonitrile solutions at 25°C

Catalytic Enantioselective Formation of C−C Bonds by Addition to Imines and Hydrazones: A Ten-Year Update

Coordination stabilised copper(I) flouride. Crystal and molecular structure of fluorotris(triphenylphosphine)copper(I)·ethanol (1/2), Cu(PPh3)3, P·2EtOH

A crown for germanium: Neutral aza- and oxamacrocycles enable stabilization of halide-free germanium(II) dications (see structure, Ge teal, N blue, C gray). The resulting structures show a marked dependence upon the denticity, donor type, and ring size of the macrocycle.

Germanium(II) dications stabilized by azamacrocycles and crown ethers.

Tetrakis(triphenylphosphine oxide) complexes of the lanthanide nitrates; synthesis, characterisation and crystal structures of [La(Ph3PO)4(NO3)3]·Me2CO and [Lu(Ph3PO)4(NO3)2]NO3

Reaction of TiCl4 or ZrI4 with the soft, neutral o-C6H4(CH2EMe)2 (E = S or Se) in anhydrous CH2Cl2 (or toluene) yields the distorted octahedral chelate complexes [MX4{o-C6H4(CH2EMe)2}]. Using Et2Se gives [MX4(Et2Se)2] (M = Zr, X = Cl or I; M = Hf, X = I). The Sn(IV) analogues, [SnCl4{o-C6H4(CH2EMe)2}] and [SnCl4(Et2Se)2] were obtained similarly. These complexes have been characterised spectroscopically and analytically, and crystal structures of trans-[SnCl4(Et2Se)2] and some selenonium salts derived as minor by-products from the parent Group 4 complexes are described. The neutral chalcogenoether complexes have been evaluated as single source precursors to ME2/ME thin films via LPCVD. [TiCl4{o-C6H4(CH2EMe)2}] leads to the deposition of air and moisture stable TiE2 films (with no residual Cl). Coverage of the substrate is uniform with platelet growth perpendicular to the surface. The heavier Zr(IV) species do not lead to significant ZrE2 deposition. On the other hand, LPCVD of [SnCl4{o-C6H4(CH2SMe)2}] leads to deposition of SnS2 at lower temperatures and SnS at higher temperatures, while [SnCl4{o-C6H4(CH2SeMe)2}] gives rather uneven coatings of SnSe2. The Et2Se derivative, [SnCl4(Et2Se)2] leads to uniform deposition of SnSe2 with growth perpendicular to the substrate surface. The SnE2/SnE films are stable indefinitely to air and moisture. The generation of TiS2, SnS2 and SnS in this way are very rare examples of metal sulfide deposition from C–S bond fission within a thioether complex.

Thio- and seleno-ether complexes with Group 4 tetrahalides and tin tetrachloride: preparation and use in CVD for metal chalcogenide films

The Ge(II) complexes [GeX2(L–L)] (L–L = 1,10-phen (X = Cl, Br); L–L = Me2N(CH2)2NMe2, 2,2′-bipy (X = Cl)), [GeX(L–L)][GeX3] (L–L = 2,2′-bipy (X = Br); L–L = pmdta (MeN(CH2CH2NMe2)2) (X = Cl, Br)) have been prepared and their crystal structures determined. The crystal structure of [GeCl2{Me2N(CH2)2NMe2}] shows a weakly associated centrosymmetric dimer based upon distorted square-pyramidal coordination at Ge(II) and containing asymmetrically chelating diamine ligands. The structure of [GeCl2(2,2′-bipy)] contains a chelating 2,2′-bipy ligand and forms a zig-zag chain polymer via long-range intermolecular Ge⋯Cl bridging interactions, leading to a very distorted six-coordinate environment at Ge. [GeCl2(1,10-phen)] adopts a weakly associated dimeric structure similar to that in [GeCl2{Me2N(CH2)2NMe2}], whereas [GeBr2(1,10-phen)] is again a zig-zag polymer similar to [GeCl2(2,2′-bipy)]. [GeBr(2,2′-bipy)][GeBr3] contains a pyramidal cation with a chelating 2,2′-bipy and a terminal Br ligand and with long-range contacts involving the three Br atoms in the anion. [GeX(pmdta)][GeX3] (X = Cl or Br) show discrete cations and anions, with no significant long-range interactions. The bonding in these systems can be described as covalent, with longer range interactions to other ligands involving the 4p orbitals of Ge. DFT calculations performed on [GeCl2(2,2′-bipy)] show that the geometry of the monomer unit in the experimental crystal structure does not correspond to the global minimum of the isolated molecule, but to a higher energy minimum. In contrast, the calculated structure of the tetramer shows some of the main structural characteristics observed in the crystal structure.

Michael Webster

Papers

Coordination stabilised copper(I) flouride. Crystal and molecular structure of fluorotris(triphenylphosphine)copper(I)·ethanol (1/2), Cu(PPh3)3, P·2EtOH

Germanium(II) dications stabilized by azamacrocycles and crown ethers.

Tetrakis(triphenylphosphine oxide) complexes of the lanthanide nitrates; synthesis, characterisation and crystal structures of [La(Ph3PO)4(NO3)3]·Me2CO and [Lu(Ph3PO)4(NO3)2]NO3

Thio- and seleno-ether complexes with Group 4 tetrahalides and tin tetrachloride: preparation and use in CVD for metal chalcogenide films

Synthesis and structural characterisation of germanium(II) halide complexes with neutral N-donor ligands