Graham A. Bowmaker

Relativistic effects in gold chemistry. I. Diatomic gold compounds

Nonrelativistic and relativistic Hartree–Fock (HF) and configuration interaction (CI) calculations have been performed in order to analyze the relativistic and correlation effects in various diatomic gold compounds. It is found that relativistic effects reverse the trend in most molecular properties down the group (11). The consequences for gold chemistry are described. Relativistic bond stabilizations or destabilizations are dependent on the electronegativity of the ligand, showing the largest bond destabilization for AuF (86 kJ/mol at the CI level) and the largest stabilization for AuLi (−174 kJ/mol). Relativistic bond contractions lie between 1.09 (AuH+) and 0.16 A (AuF). Relativistic effects of various other properties are discussed. A number of as yet unmeasured spectroscopic properties, such as bondlengths (re), dissociation energies (De), force constants (ke), and dipole moments (μe), are predicted.

The thermal decomposition of silver (I, III) oxide: A combined XRD, FT-IR and Raman spectroscopic study

FT-IR and Raman spectra for polycrystalline powders of silver (I, III) oxide, AgO, and silver (I) oxide, Ag2O, are reported. The vibrational spectra for each oxide are discussed in relation to its crystal structure, and were found to be consistent with factor group analysis predictions. Infrared and Raman spectroscopy, in conjunction with powder XRD, were also used to follow the thermal decomposition of AgO powder in air. Supplementary studies employing differential scanning calorimetry (DSC) and temperature programmed reaction (TPR), provided additional information relevant to the decomposition process. In agreement with mechanisms previously reported, AgO was thermally reduced to metallic silver ia two non-reversible steps, with the intermediate formation of Ag2O. The transformation of AgO to Ag2O occurred with heating in the 373–473 K region, while the product of this reaction remained stable to temperatures in excess of 623 K. Complete thermal decomposition of the Ag2O intermediate to Ag and O2 occurred at 673 K.

Infrared and Raman spectroscopic studies of the electrochemical oxidative degradation of polypyrrole

Abstract Electrochemical oxidative degradation of polypyrrole (PPy), known as overoxidation, in aqueous media has been studied using Raman and FT-IR spectroscopy. Raman spectroscopy was found to be the more sensitive tool to monitor the overoxidation reaction and it was found that PPy degrades at potentials as low as +0.5 V versus the saturated calomel electrode, in the presence of chloride ions. The rate of overoxidation of PPy is higher at higher potential and at higher pH.

Conducting polymers as free radical scavengers

The potential antioxidant activity of conducting polymers in biomedical applications has been evaluated by determining radical scavenging ability using the stable α,α-diphenyl-β-picrylhydrazyl (DPPH) free radical and correlating this with the reducing strength of the polymer. Commercial soluble polyaniline grafted to lignin, poly(anilinesulfonic acid), and polypyrrole, were found to be very efficient scavengers of DPPH radicals, reacting with 2-4 DPPH radicals per aniline or pyrrole monomer unit. Shifts in IR bands in the case of a polyaniline powder pointed to polymer oxidation and methoxy-substitution as likely mechanisms. All of the conducting polymers had low formal potentials (ca. 150 mV (Ag/AgCl) at pH 7), similar to those of catechin-type polyphenol antioxidants. On the other hand, the formal potentials of pyrrole and aniline were quite high (ca. 700 mV), and the reaction of aniline with DPPH radicals was limited, while o-methoxyaniline with a lower formal potential (ca. 500 mV) neutralised DPPH radicals in a 1:1 ratio.

Relativistic effects in gold chemistry. V. Group 11 dipole polarizabilities and weak bonding in monocarbonyl compounds

Hartree–Fock and Mo/ller–Plesset second order (MP2) calculations have been carried out in order to study the stability and structure of open‐shell group 11 monocarbonyl compounds MCO (M=Cu,Ag,Au). AgCO is calculated to be a very weakly bound molecule with a dissociation energy of less than 1 kJ/mol, and this casts some doubt on the previously reported identification of this species in matrix isolation studies. AuCO is stable only if relativistic effects are included, which explains the recently observed anomaly in the strength of the metal–CO interaction within the group 11 series. The metal–carbonyl interactions in CuCO and AuCO are relatively weak, with dissociation energies of about 30 kJ/mol and may be best described as a combination of dispersion, donor–acceptor (charge‐transfer) and repulsive interactions. The MP2 Cu–CO dissociation energy of 32 kJ/mol is in good agreement with the estimated experimental value of 23±6 kJ/mol. At the highest level of theory, AuCO possesses a bent geometry with a bond...

Solvent-assisted mechanochemical synthesis of metal complexes

The application of solvent-assisted mechanochemical synthesis to the study of metal complex formation is illustrated by examples involving complexes of silver halides with ethylenethiourea.

In-situ synchrotron far infrared spectroscopy of surface films on a copper electrode in aqueous solutions.

Abstract Far infrared spectra of the surface films formed upon anodic oxidation of copper have been obtained in-situ for the first time in aqueous solution environments using a synchrotron source. The spectroelectrochemical behavior of copper was studied in NaOH and in a dilute solution of KSCN in perchlorate. The oxide film at −0.05 V vs. SCE in 0.1 M NaOH solution has been identified as Cu 2 O. In the passive region at 0.3 V, CuO and Cu(OH) 2 appear to be present on the surface. Vibrational bands observed in 0.025 M KSCN+perchlorate solution are attributed to a multilayer film of copper(I) thiocyanate.

The formation and crystal and molecular structures of hexa(μ-organothiolato)tetracuprate(I) cage dianions: bis-(tetramethylammonium)hexa-(μ-methanethiolato)tetracuprate(I) and two polymorphs of bis(tetramethylammonium)hexa-(μ-benzenethiolato)-tetracuprate(I)

Abstract X-Ray analysis shows that the crystalline compounds (Me4N)2[Cu4(SMe)6] (1), (Me4N)2[Cu4(SPh)6] (2) and (Me4N)2[Cu4(SPh)6]EtOH (3) all contain the [tetrahedro-CuI4-octahedro-(SR)6]2− molecular cage. Very well developed pale yellow crystals of (2) and (3) can be obtained directly from a mixture of copper(II) salt and excess benzenethiol with tertiary amine in alcohol. The substituents R of the [Cu4(SR)6]2− cage remove the high symmetry of the Cu4S6 core, and allow three configurational isomers for the cage. All known instances of this cage structure occur as the isomer which minimises the number of close contacts of substituents over the surface of the cage. Despite this, there remain intra-cage repulsive interactions between substituents, greater for RPh than for RMe, which cause distortions primarily in the SCuS angles which range from 105–144°. CuS distances are coupled, apparently electronically, to opposite SCuS angles. The stereo-chemical analysis is extended to all known Cu4(SR)6 cages, and to alternative cage structures.

Crystal structures and spectroscopic studies of the mononuclear complex [AgBr(PPh3)2] and binuclear [Ag2X2(PPh3)4]·2CHCl3(X = Cl or Br)

The structure of the silver(I) complexes [AgBr(PPh3)2] and [Ag2X2(PPh3)4]·2CHCl3(X = Cl or Br) have been determined by single-crystal X-ray diffraction. The complex [AgBr(PPh3)2] crystallizes in the monoclinic space group C2/c and contains discrete monomeric [AgBr(PPh3)2] units with essentially trigonal-planar AgBrP2 co-ordination, and a crystallographic two-fold axis of symmetry coincident with the Ag–Br bond. The geometric parameters for the silver atom environment are: Ag–Br 2.568(1), Ag–P 2.458(2)A, P–M–P 124.14(5), P–M–Br 117.93(3)°. The complexes [Ag2X2(PPh3)4]·2CHCl3(X = Cl or Br) are isomorphous, monoclinic, space group C2/c, and contain [Ag2X2(PPh3)4] dimers. Each of the two silver atoms in the structure is four-co-ordinated by forming bonds with the P atoms of the two phosphine ligands and the two doubly bridging halide atoms. The Ag and X atoms lie in a plane, and each of the molecules in the unit cell has a C2 axis which passes through the two X atoms. A chloroform molecule is hydrogen bonded to each X atom. The far-IR spectra of these complexes show bands which are assigned to ν(AgX) modes, and the spectra of these and the unsolvated dimer [Ag2Cl2(PPh3)4] are analysed to yield information about the Ag–X bonding. The Raman spectrum of [AgBr(PPh3)2] shows a band which is assigned to a ν(AgP) mode, an assignement which is confirmed by the observation of similar bands in the Raman spectra of the isostructural gold(I) complexes [AuX(PPh3)2](X = Cl, Br or I). The solid-state cross-polarization magic-angle spinning (CP MAS)31P NMR spectra of the silver complexes show multiplets die to 1J(AgP) coupling. The spectra of the dimers show separate chemical shifts for the crystallographically inequivalent phosphorus atoms, and 2J(PP) coupling between these atoms. The splitting patterns are interpreted in terms of the silver co-ordination environment.

The formation and structural chemistry of the hexa(μ-t-butylthiolato) pentacuprate(I) cage anion with triethylammonium and tetraethylammonium cations

Abstract Yellow (Et4N)[Cu5(SBut)6] crystallises from solutions prepared from Cu(II), ButSH, Et3N and Et4NBr in acetone/ethanol, while (Et3NH)[Cu5(SBut)6] crystallises from solutions of CuSBut and ButSH in Et3N. Crystal structure determinations reveal that both compounds contain the molecular cage [Cu5(μ-SBut)6]−, in which two copper atoms are three-coordinate (Cutrig), three copper atoms are two-coordinate (Cudig), and all thiolate ligands are doubly-bridging. The polyhedral stereochemistry of the core is trigonal bipyramido-Cu5-trigonal antiprismo-S6. The complete [Cu5(μ-SBut)6]− cage in the Et4N+ compound closely approaches D3 symmetry, but in the Et3NH+ compound one SBut ligand is inverted at the sulphur bridge, causing angular distortions in the cage. Two structural features, the antiprismatic twist of the S6 polyhedron and the bending of Cudig towards the cage centroid (S-Cudig-S = 171(1)°), provide evidence for weak Cu-Cu attractive interactions within the cage. Infrared data are discussed. Crystal data: (Et4N)[Cu5(SBut)6], C32H74Cu5NS6, a = 45.500 (3), b = 11.805(1), c = 20.168(2) A, β = 117.81 (1)°, C2/c, Z = 8, R = 0.078 (2953 observed F); (Et3NH)[Cu5(SBut)6], C30H70Cu5NS6, a = 10.519(1), b = 21.457(1), c = 20.065(1), β = 95.11(1), P21/c, Z = 4, R = 0.072 (3093 observed F). (Et4N)[Ag5(SBut)6] is isostructural with (Et4N)[Cu5(SBut)6].