Phenyl thiazyl compounds: Synthesis and electrical conductivity

A series of substituted phenylene-dithio-bis(phenyldithiazyl) (PDBPD) and phenylthiophenyldithiazyl (PTPD) compounds have been synthesized utilizing the facile reaction between N-trimethyl silylimides and aromatic sulfenyl chlorides. The compounds are insulators with conductivities of 10^?8–10^?12 (Ω cm)^?1. However, they can be oxidized with Br₂ to conductivities of 10^?3–10^?5 (Ω cm)^?1 for pressed pellets. Electron donating and withdrawing substituents on the phenyl ring markedly alter the electrical transport properties. While PTPD compounds are soluble in many solvents, the PDBPD derivatives are only sparingly soluble.     

Structure and bonding in cluster compounds of gold

Recently a number of high nuclearity gold cluster compounds of the type [Au(AuPR₃)_n]^x+ have been synthesised and structurally characterised using single crystal X-ray crystallographic measurements. The structures and properties of these compounds are contrasted with those of comparable high nuclearity metal carbonyl cluster compounds. In order to account for the structures of [Au(AuPR₃)_n]^x+ in the solid state and in solution it has proved necessary to develop a flexible bonding model which emphasises the topologies of the clusters rather than their detailed geometries. In this fashion the observed stereochemical non-rigidity of these compounds in solution is readily accounted for. In the solid state the structures of the higher nuclearity cluster cations can be derived either from the centred chair [Au(AuPR₃)₆], or the centred crown [Au(AuPR₃)₈] by adding edge or face capping AuPR₃ fragments. The bonding in heterometallic clusters containing the AuPR₃ fragment is also considered.     

Reactions of chlorine monofluoride with tetrasulphur tetranitride,thiazyl chloride and thiazyl fluoride

Chlorine monofluoride reacts with tetrasulphur tetranitride to give thiazyl chloride (monomer and trimer) and thiazyl fluoride; with further ClF, NSCl reacts to form NSF then ClNSF₂, and finally N₂, Cl₂ and SF₄. The reaction NSCl/ClF to give NSF/Cl₂ reverses in SO₂ solvent due to removal of ClF as SO₂ClF. NSF was prepared, in a new method, by passing NSCl through a column of CsF at 110°.     

An electron localization function investigation of bonding in some simple four‐coordinate nitrogen and phosphorus compounds

The bonding in some simple four‐coordinate species involving nitrogen and phosphorus has been studied by the electron localization function (ELF) approach and compared to that in their conventionally singly and doubly bonded counterparts. Despite evidence suggesting the presence of a conventional multiple bond in certain cases of the four‐coordinate species, the ELF study shows this not to be the case. Rather, the situation is better pictured as, for example, in the case of H₃PCH₂as where both ionic and covalent interactions are present, a type of bond we term cov‐ionic. While the ionic interaction is generally strong, the covalent part can be weak, as in the case of the four‐coordinate nitrogen compounds, or strong, as in the case of the four‐coordinate phosphorus species. The quantum mechanically determined properties of the cov‐ionic bonded compounds are consistent with this picture. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:341–352, 2000     

The bonding in boron and transition-metal cluster compounds

A method is described for constructing qualitatively the molecular orbitals of an approximately spherical cluster of boron or transition-metal atoms. The method gives a way of understanding the electron-counting rules for such clusters, the preference for deltahedral structures, the relationship between closo boranes on the one hand and nido and arachno boranes on the other, and Mingos' capping and condensation principles for transition-metal clusters.     

Hydrogen bonding in nylon 66 and model compounds

Fourier-transform infrared spectroscopy was used to study the hydrogen bond-breaking process in nylon 66 and two model compounds. The resulting enthalpy and entropy values indicated that while there is no interaction between adjacent amide groups in the polymer chain, there is, nevertheless, a substantial cooperative effect in the transverse hydrogen bond direction. We have also established that any analysis of hydrogen bond breaking in semicrystalline polymers (i.e., nylon 66) below the melting point should include a crystallinity correction factor. Extrapolation of our data above the melting point of nylon 66 yielded a 26% retention of hydrogen bonding.     

Structure and bonding in [M6X8] units of nonmetallic transition metal cluster compounds

A simple quantum mechanical method, based on the Wolfsberg-Helmholtz approximation, has been applied to some nonmetallic4d and5d transition metal cluster compounds containing M₆X₈ units. Our aim was to calculate bonding energies ofM₆ clusters as a function of electronic configuration and symmetry. Energy sequences of clusters containing elements adjacent to each other in the periodic table are discussed, in particular, niobium and molybdenum as well as tungsten and rhenium. Compared with experimentally well-characterized compounds, the computional results show good qualitative agreement. So the occurrence ofM₆ clusters withO_h or lower symmetry can be explained by electronic effects.     

Inclusion of thiazyl radicals in porous crystalline materials

The incorporation of benzodithiazolyl (BDTA) and methylbenzodithiazolyl (MBDTA) radicals into porous hybrid frameworks via gas phase diffusion revealed that inclusion appeared selective for the MIL53(Al) framework against a range of other potential hosts. Both PXRD and EPR studies are consistent with retention of a π*-π* dimer motif for BDTA in MIL53(Al)@BDTA whereas MBDTA in MIL53(Al)@MBDTA appears to be monomeric. The guests are readily released by the addition of solvent (CH(2)Cl(2)).     

Structure and bonding in the PtCO isoelectronic series

The equilibrium geometries and harmonic frequencies of PtXY, XY = CO, N₂, CN⁻ and NO⁺, in the ¹∑⁺ state have been calculated by the ab initio self-consistent field method with gradients using appropriate effective core potentials. An analogous analysis was also carried out on the free ligands for comparison purposes. The ligands are compared with respect to changes in X-Y bond lengths and stretch frequencies upon complexation, and Pt-XY bond lengths, stretch frequencies and bond energies. The calculated results for PtCO and PtN₂ are compared with matrix-isolated infrared spectra.     

Chemical bonding in oblatonido ditantalaboranes and related compounds

Abstract  

The recently discovered ditantalaboranes Cp₂Ta₂B _n H _n+6 (n = 4, 5) are isoelectronic with the previously discovered dimetallaboranes Cp₂M₂B _n H _n+4 of the group 6 metals Cr, Mo, and W where Cp = η⁵-cyclopentadienyl or substituted cyclopentadienyl. Their oblatonido polyhedral structures can be derived from the oblate (flattened) deltahedra of the oblatocloso dirhenaboranes Cp₂Re₂B _n+1H _n+1 by removal of an equatorial BH vertex with adjustment of the skeletal electron count by changing the metal atoms and adding hydrogen atoms. In these oblatocloso dirhenaborane deltahedra, the approximately antipodal rhenium atoms are close enough together to form a formal Re=Re double bond with lengths in the range 2.69–2.82 ?. Similarly, short M=M distances are maintained in the related oblatonido derivatives Cp₂Ta₂B _n H _n+6 (n = 4, 5) and Cp₂M₂B _n H _n+4 (M=Cr, Mo, W). However, the synthesis of Cp₂Ta₂B _n H _n+6 (n = 4, 5) from CpTaCl₄ + LiBH₄/BH₃ also gives a less-reduced product Cp₂Ta₂Cl₂B₅H₁₁ with a longer Ta–Ta distance of ~3.2 ?. This may be regarded as a formal single bond bridged by one of the hydrogen atoms. Vertices of degree 5 (excluding terminal atoms/groups but not edge-bridging hydrogens) are sites of highest stability/lowest chemical reactivity not only in metal-free boranes but also in the dimetallaboranes discussed in this paper. For example, all four boron vertices in Cp₂Ta₂B₄H₁₀ have the favorable degree or 5.     

Structure and hydrogen bonding in polyhydrated complexes of guanine

Abstract Molecular structure of complexes of guanine with 12, 13, 16, and 17 water molecules were calculated using B3LYP/6-311G(d,p) level of theory. Interaction with water results in some deformation of geometrical parameters of guanine, which can be described as contribution of zwitter-ionic resonant form into the structure of DNA base. Saturation of water binding sites within guanine creates possibilities for the formation of the N···H–O hydrogen bond where the nitrogen atom of amino group acts as proton acceptor. The NBO analysis of guanine–water interactions reveals that hydrogen bonds involving the N(3) and N(7) atoms of guanine represent a case of mixed N···H–O/π···H–O hydrogen bonds where contribution of π-system into total energy of interaction varies from 3% to 41%. This contribution significantly depends on orientation of the hydrogen atom of water molecule with respect to plane of purine bicycle and influence of neighboring water molecules. Graphical Abstract