Matthew J. Almond

The photodimerisation of trans-cinnamic acid and its derivatives: a study by vibrational microspectroscopy.

Infrared and Raman spectroscopies have been used to monitor the [2 + 2] photodimerisation reactions of alpha-trans-cinnamic acid and of a number of its derivatives. The principal changes observed in the spectra upon dimerisation are decay of a band around 1637 cm(-1), which is assigned to v(C=C) of the ethene bond of the monomer, and growth of bands just above 3000 cm(-1), which result from v(C-H) of saturated carbon atoms of the dimer. The use of microscope attachments has allowed us to follow the reactions of single crystals and we conclude that the reactions are topotactic in nature. We have carried out preliminary kinetic experiments in which spectra of one single crystal are recorded after sequential periods of photolysis. We find that the rates of dimerisation of differently substituted cinnamic acids are similar, with physical effects, such as the thickness of an individual crystal, outweighing any observed electronic effects (inductive or mesomeric).

The use of FT-IR as a screening technique for organic residue analysis of archaeological samples

A range of archaeological samples have been examined using FT-IR spectroscopy. These include suspected coprolite samples from the Neolithic site of Catalhöyük in Turkey, pottery samples from the Roman site of Silchester, UK and the Bronze Age site of Gatas, Spain and unidentified black residues on pottery sherds from the Roman sites of Springhead and Cambourne, UK. For coprolite samples the aim of FT-IR analysis is identification. Identification of coprolites in the field is based on their distinct orange colour; however, such visual identifications can often be misleading due to their similarity with deposits such as ochre and clay. For pottery the aim is to screen those samples that might contain high levels of organic residues which would be suitable for GC-MS analysis. The experiments have shown coprolites to have distinctive spectra, containing strong peaks from calcite, phosphate and quartz; the presence of phosphorus may be confirmed by SEM-EDX analysis. Pottery containing organic residues of plant and animal origin has also been shown to generally display strong phosphate peaks. FT-IR has distinguished between organic resin and non-organic compositions for the black residues, with differences also being seen between organic samples that have the same physical appearance. Further analysis by GC-MS has confirmed the identification of the coprolites through the presence of coprostanol and bile acids, and shows that the majority of organic pottery residues are either fatty acids or mono- or di-acylglycerols from foodstuffs, or triterpenoid resin compounds exposed to high temperatures. One suspected resin sample was shown to contain no organic residues, and it is seen that resin samples with similar physical appearances have different chemical compositions. FT-IR is proposed as a quick and cheap method of screening archaeological samples before subjecting them to the more expensive and time-consuming method of GC-MS. This will eliminate inorganic samples such as clays and ochre from GC-MS analysis, and will screen those samples which are most likely to have a high concentration of preserved organic residues.

Organometallic precursors to the formation of GaN by MOCVD: structural characterisation of Me3Ga · NH3 by gas-phase electron diffraction

Abstract The molecular structure of Me3Ga · NH3 [I] has been studied by gas-phase electron diffraction at 25°C. The experimental data are fitted by a model in which the C3GaN core of the molecule has C3v symmetry. The molecule was defined in terms of four bond distances, three valence angles and two torsion angles. Of the bond distances three were refined (rg(GaN) = 2.161(22)°, rg(GaC) = 1.979(3) A, rg(CH) = 1.109(7) A). It was necessary to hold the fourth bond distance at an assumed value [rg(NH) = 1.045 A]. Two of the valence angles were refined (NGaC = 101.8(62)°, GaCH = 111.3(16)°) with the third (GaNH) being held at 109.0°. The torsion angle HN / GaC was held at 60.0° while the remaining torsion angle HC / GaN was refined to 37.5(224)°. The dependent angle CGaC was 115.9(42)°, so the C3Ga fragment is not far from planar, which is in accord with the lone pair from the nitrogen atom being donated into the pz orbital on the gallium atom. This suggestion is supported by the gas-phase and low temperature infra-red spectroscopic data that are reported. Evidence is also presented suggesting the GaN bond is weak and thus it is not surprising that when NH3 and Me3Ga are used to grow GaN it is necessary to use NH3 / Me3Ga ratios greater than one.

The photodimerisation of the α- and β-forms of trans-cinnamic acid: a study of single crystals by vibrational microspectroscopy

Abstract Infrared and Raman microspectroscopy have been used to follow the photodimerisation reactions of single crystals, the α- and β-forms of trans-cinnamic acid. This approach allows the starting materials and products—α-truxillic acid that has Ci symmetry and β-truxinic acid, which has Cs symmetry—to be identified. It also allows the topotactic nature of the reaction to be confirmed. Attempts to produce the poorly-defined unreactive γ-form of trans-cinnamic acid resulted only in a mixture of the α- and β-forms. The findings suggest a wide role for these spectroscopic methods in monitoring solid-state organic reactions.

The microstratigraphy of middens: capturing daily routine in rubbish at Neolithic Çatalhöyük, Turkey

Microstratigraphy — the sequencing of detailed biological signals on site — is an important new approach being developed in the Çatalhöyük project. Here the authors show how microscopic recording of the strata and content of widespread middens on the tell are revealing daily activities and the selective employment of plants in houses and as fuel. Here we continue to witness a major advance in the practice of archaeological investigation.

Reactions of alkenes with ozone in the gas phase: a matrix-isolation study of secondary ozonides and carbonyl-containing reaction products

Gas phase ozonolysis reactions of the alkenes ethene, cis- and trans-but-2-ene, isoprene and the monoterpenes alpha-pinene, beta-pinene, beta-carene, limonene and beta-myrcene have been carried out and the reaction products have been trapped in O2-doped-argon matrices onto a Csl window held at 12 K. Products have been identified by IR spectroscopy. Comparison with previous matrix spectra, where secondary ozonides have been generated either in situ by annealing or in solution reactions allows a positive identification of the secondary ozonides of ethene and of cis- and trans-but-2-ene to be made. These observations are backed up by experiments utilising the isotopes 13C and 2H (D). It appears that secondary ozonides have also been formed from isoprene and the range of monoterpenes studied; this hypothesis is based upon the similarity of spectral features seen in the products of these reactions within those of the simpler alkenes. A number of other primary and secondary products are also identified from these reactions. Ethene gives formaldehyde as a primary product and acetaldehyde as a secondary product; it is found that the yield of acetaldehyde compared to formaldehyde increases as the reaction times are increased. Formaldehyde, one of the expected primary products, is formed by ozonolysis of beta-pinene, although the other expected primary product, nopinone, is not seen. A range of secondary reaction products have been identified from the ozonolysis of the monoterpenes studied.

Novel low-temperature route to known (MnS and FeS2) and new (CrS3, MoS4 and WS5) transition-metal sulfides

The reaction of the transition-metal carbonyls, Mn2(CO)10, Fe(CO)5 or M(CO)6(M = Cr, Mo or W) with sulfur in 1, 2-dichlorobenzene yields polycrystalline MnS (alabandite), FeS2(marcarsite), and three new amorphous sulfur-rich sulfides CrS3, MoS4 and WS5.

PHOTOCHEMICAL AND THERMAL SYNTHESIS OF METAL CARBONYL COMPLEXES OF TETRAALKYL DIPHOSPHINE DISULFIDES M(CO)4(R2P(S)P(S)R2) (M = MO, W; R = ME, ET, PR-N , BU-N)

Abstract The new complexes [M(CO)4(R2P(S)P(S)R2)], 1A-1D, 2A-2D, (1A, M  Mo, R  Me; 1B, M  Mo, R  Et; 1C, M  Mo, R  Pr-n; 1D, M  Mo, R  Bu-n; 2A, M  W, R  Me; 2B; M  W, R  Et; 2C, M  W, R  Pr-n; 2D, M  W, R  Bu-n) have been prepared either by the photochemical reaction of M(CO)6 with R2P(S)P(S)R2, or by thermal displacement of coordinated norbornadiene in C7H8Mo(CO)4 with R2P(S)P(S)R2, to give the complexes [M(CO)4(R2P(S)P(S)R2)]. The complexes have been characterized by elemental analysis, IR and 31P-[1H]-NMR spectroscopy and FAB-Mass spectrometry; the spectroscopic studies suggest a cis-chelate dibentate coordination of the ligand.

A single crystal x-ray diffraction study of yttrium tartrate hydrate [Y(C4H4O6)(C6H5O6) ·2.5H2O]

Abstract Yttrium tartrate hydrate [Y(C4H4O4)(C4H5O6) · 2.5H2O] (A) has been prepared by the reaction of YC13 with tartaric acid in alkaline solution. It is believed that the two tartrate anions, while crystallographically equivalent, have different charges, one being -1 and the other -2. In A the yttrium centre is coordinated to nine oxygen atoms. These nine oxygen atoms originate from four tartrate ligands which are crystallographically identical and from three water molecules, one of which has an occupancy factor of 50%. The metal takes part in two symmetry-related, five-membered chelate rings formed by carboxyl and α-hydroxyl groups from each of two tartrate ligands. The carboxyl groups also form bidentate bridges linking two metal centres. The tartrate groups thus interconnect to give a three-dimensional layered structure to the compound. The coordination at each yttrium centre is completed by three water molecules, one of which is unique. The Y—O distances in the five-membered rings are 2.324(14) (carboxyl oxygen) and 2.489(11)(hydroxyl oxygen). The results of studies utilizing elemental analysis, powder X-ray diffraction and IR spectroscopy support the single crystal diffraction findings. Copyright

Rapid characterisation of archaeological midden components using FT-IR spectroscopy, SEM-EDX and micro-XRD

Samples taken from middens at the Neolithic site of Catalhöyük in Turkey have been analysed using IR spectroscopy backed up by powder XRD and SEM-EDX. Microcomponents studied include fossil hackberries (providing evidence of ancient diet and seasonality), mineral nodules (providing evidence of post-depositional change) and phytoliths (mineralised plant cells, providing evidence of usage of plant species). Finely laminated ashy deposits have also been investigated allowing chemical and mineralogical variations to be explored. It is found that many layers which appear visually to be quite distinctive have, in fact, very similar mineralogy.