Iron phthalocyanine (FePc) has been studied using Fe-57 Mossbauer spectroscopy, to obtain information which helps in understanding the gas-sensing properties of phthalocyanines. The isomer shift values of the alpha and beta phases (0.46 and 0.49 with respect to alpha-Fe) occur between high-spin and low-spin iron(II) ion. The quadrupole values (2.50 and 2.62) are characteristic of high-spin iron(II). The variable-temperature studies have determined different Debye temperatures (theta(D)) and recoil fractions at room temperature (f(300)) for the alpha and beta phases, respectively: theta(D) = 143 and f(300) = 0.14; theta(D) = 199 and f(300) = 0.36. This indicates a more rigid structure for the beta-phase, consistent with the presence of the two additional nitrogen interactions, absent in the alpha-phase, giving an octahedral structure.

Fe-57 Mossbauer spectroscopy has been used to examine a number of phosphate glasses containing iron a as alpha-Fe2O3. Glasses melted for a long duration in air gave a Fe3+/Fe2+ ratio of 60140 whilst those melted in an inert atmosphere showed a total absence of Fe3+ and those melted for a short duration in air gave a 85/15 ratio. A quadrupole splitting distribution programme was used to fit the spectra in terms of ferric and ferrous iron envelopes. For the glass melted in air, this yielded Gaussian profiles indicative of octahedral sites for both Fe3+ and Fe2+. The Fe2+ profile of the glass melted in the inert atmosphere and the Fe3+ profile of the glasses melted for the short time were both resolved into two Gaussians. In each case, one was similar to that for the glass melted in air whilst the second represented more disordered iron sites. Two distinct types of iron site appear to be present in these glasses, one preferentially occupied by Fe3+ and the other by Fe2+. Adjustment of the Fe3+/Fe2+ ratio causes both types of site to be occupied by either Fe3+ or Fe2+.

Fe-57 Mossbauer spectra of phosphate glasses containing iron obtained over a temperature range 12-600 K consisted of two broadened quadrupole doublets characteristic of octahedral Fe3+ and Fe2+ sites. No compositional trends could be discerned. The temperature dependence of the absorption areas and isomer shifts were fitted to equations derived from the Debye model of solids with appropriate approximations to the relevant Debye integrals. Absorption area data yielded theta(D) approximately 320 K for Fe3+ and approximately 240 K for Fe2+, leading to a room temperature recoilless fraction ratio f(Fe3+)/f(Fe2+) approximately 1.3. The second order Doppler shift of the isomer shift yielded theta(D) approximately 400-565 K for Fe3+ but the poor quality of the Fe2+ data prevented accurate fitting. A crystal field splitting model used to analyse the temperature dependence of the ferrous iron quadrupole splitting yielding average splittings DELTA1 approximately 360 cm-1 and DELTA2 approximately 900 cm-1. The lattice component of the Fe2+ quadrupole splitting was consistently larger than the Fe3+ splitting, suggesting that the Fe2+ sites are more disordered than the Fe3+ sites.

The efficient synthesis of a range of highly polar novel zwitterionic D-π-A adducts of tetracyanoquinodimethane (TCNQ) has been established and derivatives with an alkyl chain as short as eight carbon atoms have been fabricated as Langmuir–Blodgett (LB) films.

This work is concerned with the development of a technique to observe the onset of corrosion as it occurs beneath a temporary protective layer. Such temporary protectives include paints, varnishes, greases and oils that are applied to metal surfaces to give short-term protection from corrosion. The objective of this project was to develop a technique that could be used to evaluate the effectiveness of various temporary protectives in different environments, without the need to remove the protective layer, thus eliminating the possibility of any chemical changes or loss of corrosion products occurring as a result of removal. The temporary protective layers are typically 25Μm for paints and 15Μm per layer for varnishes. The 6.3 keV fluorescence X-ray is able to penetrate such layers, but the large escape depth (∼10Μm) of the X-rays means that for a thin protective layer a large proportion of the X-rays detected will originate from deep within the substrate and the resultant spectrum will be representative of the bulk rather than the surface. To enhance the surface sensitivity of the CXMS technique, the near surface region must be enriched in the isotope Fe-57. To achieve this, Fe-57 was vacuum evaporated onto the surface of mild steel substrates and subsequently diffused into the near surface region. An approximate 20 nm Fe-57 layer was deposited onto mild steel samples. The surface enriched samples were then annealed to allow the Fe-57 to diffuse into the near surface region of the mild steel substrate, and also to allow back diffusion of the substrate. A diffusion model was developed to predict the surface distribution of Fe-57 as a function of annealing parameters. The computer diffusion model allowed the ideal annealing conditions to be estimated to obtain a required near surface environment. It was essential that the annealing conditions did not result in any surface oxidation, and did result in a surface that was characteristic of mild steel. CEMS and CXMS spectra were recorded of samples before and after annealing, and also dynamic Secondary Ion Mass Spectrometry (SIMS) was used to monitor the enrichment and diffusion process. Energy Dispersive X-ray Analysis (EDXA) was also used to characterize the surface. A number of enriched samples were prepared and treated with a variety of surface temporary protectives. The CXMS spectra were recorded before and after exposure of the coated samples to various aggressive environments.

Charge distribution in two monocationic bimetallic organoiron complexes, prepared by transfer of Fp+ to Fp acyl and vinyl species [Fp = Fe(CO)2(C5H5)], have been studied by 57Fe Mössbauer spectroscopy, demonstrating that a considerable degree of polarisation is present in linear organic π-systems interposed between organometallic donor and acceptor groups.

AbstractThe fate of a series of triphenyltin biocides on incorporation into neoprene elastomers has been studied by 119mSn Mössbauer spectroscopy, together with supporting chemical derivatization techniques. It is shown that triphenyltin compounds undergo drastic degradation on incorporation into neoprene, suffering cleavage of phenyl–tin bonds to give a mixture of products in which all stages of dephenylation are present, including stannic chloride. This degradation occurs not only in elastomers cured at 150°C, but also in room temperature solvent‐cast samples.

AbstractThe fate of a series of tributyltin toxicants on incorporation into cured neoprene elastomers has been studied by 119mSn Mössbauer and 119Sn NMR spectroscopic techniques, together with supporting chemical derivatization techniques. It is shown that all of the toxicants undergo chemical change during the curing process, being converted into tributyltin chloride, together with (in some cases) tributyltin stearate and a small amount of dibutyltin distearate. Possible interactions between the organotin agents and other components of the elastomer, e.g. carbon black filler, and cure accelerators such as tetramethylthiuram disulphide, have also been investigated.

Organotin stabilizers of the type Bu 2 SnX 2 (X = SCH 2 CO 2 C 8 H 17 or O 2 CCHCHCO 2 C 8 H 17 ) present in poly(vinyl chloride) (PVC) and subjected to varying doses of gamma irradiation in the range 1–200 kGy (0.1–20 Mrad) are shown to suffer degradation with dealkylation to form monobutyltin trichloride and tin(IV) chloride, which have been characterized by a subsequent alkylation procedure followed by gas chromatographic analysis. The extent of degradation of the stabilizers on prolonged gamma irradiation is much more severe than during thermal degradation leading to comparable blackening of the polymer.

AbstractVariable‐temperature Sn‐119m Mössbauer studies of tin(IV) chloride (SnCl4) and dibutyltin dichloride (Bu2SnCl2) when dispersed in a poly(vinyl chloride) (PVC) matrix have been interpreted using a Debye model. Recoilless fractions have been determined which indicate that at 80 K the Mössbauer technique is nearly three times as sensitive to the presence of SnCl4 compared with Bu2SnCl2 within the poly(vinyl chloride) matrix. These observations have been explained in terms of structural changes occurring on dispersion in the polymer matrix which result in the tin atom in tin(IV) chloride becoming six‐coordinate whereas that in dibutyltin dichloride reduces its coordination to five. The implications of these results for future applications of Mössbauer spectroscopy to the study of organotin compounds present in polymers are considered.

The technique of 119mSn Mössbauer spectroscopy has been used to study the changes which occur in three organotin stabilisers within a PVC matrix when exposed to doses of γ-irradiation up to 20 Mrad. The stabilisers studied were dioctyltinbis(iso-octylthioglycollate) [Oct2Sn(IOTG)2], dibutyltinbis(iso-octylthioglycollate) [Bu2Sn(IOTG)2] and dibutyltinbis(iso-octylmaleate) [Bu2Sn(IOM)2] incorporated into the PVC at the appropriate commercial level by conventional hot milling techniques or solvent casting. Extended doses up to 20 Mrad showed that the final degradation product for all three stabilisers is SnCl4 and that the rate of degradation depends not only upon the type of stabiliser but also upon the extent of thermo-mechanical damage suffered by the PVC during processing. Mössbauer spectra were recorded at intermediate doses in the range 0·1 to 10 Mrad and yielded complex spectra containing unresolved lines corresponding to mixtures of original stabilisers and degradation products. Intermediate degradation products are proposed and rapid conversion to SnCl4 is observed to start at doses greater than 3 Mrad.

119mSn Mossbauer spectroscopy has been used to study the chemical changes undergone by a range of tin-containing stabilisers (dialkyltin dilaurates, dialkyltin bis(ethylcysteinates), stannous stearate and stannous cysteinate) during thermal degradation of PVC at 185°C. The dialkyltin-laurate and -cysteinate stabilisers are converted to the dialkyltin dichlorides. Stannous stearate and stannous cysteinate are rapidly converted into stannic oxide and stannic chloride, respectively.

The technique of 119m Sn Mössbauer spectroscopy has been used to study the changes which occur in three organotin stabilisers within a PVC matrix when exposed to doses of γ-irradiation up to 20 Mrad. The stabilisers studied were dioctyltinbis(iso-octylthioglycollate) [Oct 2 Sn( IOTG ) 2 ], dibutyltinbis(iso-octylthioglycollate) [Bu 2 Sn(IOTG) 2 ] and dibutyltinbis(iso-octylmaleate) [Bu 2 Sn(IOM) 2 ] incorporated into the PVC at the appropriate commercial level by conventional hot milling techniques or solvent casting. Extended doses up to 20 Mrad showed that the final degradation product for all three stabilisers is SnCl 4 and that the rate of degradation depends not only upon the type of stabiliser but also upon the extent of thermo-mechanical damage suffered by the PVC during processing. Mössbauer spectra were recorded at intermediate doses in the range 0·1 to 10 Mrad and yielded complex spectra containing unresolved lines corresponding to mixtures of original stabilisers and degradation products. Intermediate degradation products are proposed and rapid conversion to SnCl 4 is observed to start at doses greater than 3 Mrad.

AbstractDie Reaktion der Sn‐tetrachloride mit Tetrakis‐ [3‐furyl]‐zinn führt beim Erhitzen abhängig vom Molverhältnis zu den flüssigen Produkten (Ia) oder zu den Verbindungen (Ib) (Ausb. in g), die in Toluol mit äquimolaren Mengen des Phosphinoxids die Komplexe (II) liefern.

The solid state structure of the triphenylphosphine oxide (TPPO) adduct of tri-3-thienyltin bromide has been investigated by both single crystal X-ray analysis and Mössbauer spectroscopy. The crystal structure consists of discrete molecules and there is no evidence of any intermolecular tin-sulphur interactions. Each tin atom is found to be in a five-coordinate trigonal bipyramidal environment in which the three thienyl groups occupy equatorial positions. The metal atom is displaced by 0.182 Å out of the equatorial plane and towards the axial bromine. Two of the thienyl ligands exhibit rotational disorder and the lack of disorder in the remaining heteroaryl ligand is attributed to the close proximity of this group to a phenyl ligand. The Mössbauer parameters are also in accord with five-coordination for tin and are indicative of the aryl groups being equatorial.