The structures of two complex layered oxide-fluorides have been determined from the analysis of room temperature X-ray and constant wavelength neutron powder diffraction data. Bi2TiO4F2 and Bi2NbO5F adopt a single layer Aurivillius-type structure with an ordered array of fluoride/oxide anions. The structure of Bi2TiO4F2 has also been studied at 24 K using time-of-flight neutron powder diffraction, which is well below the previously reported ferroelectric transition temperature. The structures of both materials can be described in the tetragonal space group I4/mmm, but show significant atomic displacements from the positions described in the original structural models proposed for these compounds as a result of disordered tilts and/or distortions of the M(O,F)(6) octahedra. No three-dimensional long-range ordered structural distortion was observed upon cooling of Bi2TiO4F2 to 24 K. F-19 MAS NMR data have been collected and support the presence of only one fluoride site. Bond valence calculations allow the assignment of the oxide and fluoride ions within the structure, and the proposed model has the fluoride ions located in the equatorial sites of the titanium or niobium octahedra.

The influence of molecular conformation on the oxidation (ionisation) potential and electronic structure associated with several TPD-style hole transport materials has been assessed through a combination of single crystal X-ray diffraction, electrochemical and spectroelectrochemical methods and DFT calculations. The introduction of methyl groups can be used to tune the ionisation potential of these molecular species through a combination of electronic (inductive) and thermodynamic effects, while the conformation of the biphenyl portion of the molecular framework is found to play the greatest role in determining the Marcus-type reorganisation energy associated with the charge transport process on the molecular level.

The compounds N,N,N′,N′-tetra(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (4), N,N,N′,N′-tetra(4-methylphenyl)-(2,2′-dimethyl)-(1,1′-biphenyl)-4,4′-diamine (5a) and N,N,N′,N′-tetra(4-methylphenyl)-(2,2′,6,6′-tetramethyl)-(1,1′-biphenyl)-4,4′-diamine (6a) undergo two reversible one electron oxidations. The first oxidation potential increases in the order 4 < 5a < 6a, while the separation between the first and second oxidation decreases in the reverse order 4 (0.30 V) > 5a (0.16 V) > 6a (0.00 V), reflecting the decreasing thermodynamic stability of the radical cations [4+] > [5+] > [6a+]. Electronic spectroscopy and spectroelectrochemistry (UV-Vis-NIR) confirm expectations, and the introduction of methyl groups at the 2,2′ and 6,6′ positions of the 1,1′-biphenyl moiety electronically decouple the arylamine moieties. In contrast, N,N,N′,N′-tetra(phenyl)-(2,2′-dimethyl)-(1,1′-biphenyl)-4,4′-diamine (5b) and N,N,N′,N′-tetra(phenyl)-(2,2′,6,6′-tetramethyl)-(1,1′-biphenyl)-4,4′-diamine (6b) give much less kinetically stable radical cations upon oxidation, which oligomerise/polymerise through the 4 positions of the N-phenyl groups via a step-growth process. The molecular and crystal structures of 4 and 6b are also reported.

Poly(aryl)amine based charge transfer materials (CTMs) are essential components in a range of present and future technologies, from the Xerox process to display devices based upon light emitting polymers (LEPs). However. there is a lack of detailed understanding regarding the electronic properties of CTMs in their various neutral and oxidized forms. This paper reports the use of an optically transparent thin layer electrochemical (OTTLE) cell in combination with a Raman microprobe system and DFT calculations to provide information on the molecular and electronic structure of the mono- and di-oxidized derivatives of the classic CTM N,N'-diphenyl-N,N"-bis (3-methylphenyl)(1,1'-biphenyl)-4,4'-diamine (TPD) and the closely related species N,N'-diphenyl-N,N'-bis(2,4-dimethylphenyl)(1,1'-biphenyl)-4,4'-diamine (DMTPD). The resonance Raman scattering profile easily discriminates between the monovalent and divalent cations while DFT calculations permit correlation of the observed vibrational frequencies with localized atomic displacements. The cations are best described in terms of a symmetrical (i.e. fully delocalized) structure. The high sensitivity of the method suggests that it should be appropriate for the observation of low concentrations of the various cations generated from TPD type CTMs during device operation.

Light emitting polymers (LEPs) are poised to become the predominant display technology within this decade. Charge transfer materials (CTMs) within these LEPs are important as they aid the efficiency of the electroluminescence emitted from the devices. Since many of these materials are strong Raman scatterers, Raman microscopy would provide an ideal method for investigating CTMs in-situ in the polymer matrix. The Raman spectra of the widely used CTMs based on triphenylamines are assigned for three different substituted monomers and for selected dimers and trimers. Theoretical calculations using the hybrid BPW91 functional and split-valence polarised 6G(d) basis set were performed, and the Raman scattering frequencies calculated and compared with those from experimental materials. A good correlation was found between the computed and experimental frequencies for the monomers. The largest deficit was 29 cm−1 for any clearly assigned band, and there was an average error of 9.4 cm−1 for the five most intense bands. The experimental Raman spectrum of the dimer dimethyltriphenyldiamine (DMTPD) and the calculated Raman active vibrations of methyltriphenyldiamine (MTPD) show few significant changes compared to the monomer. Comparison of the experimental trimer spectra with monomer calculations also show that simplified DFT calculations may confidently be used for assigning many bands in larger polymeric CTMs.

The importance of polymorphism in crystallisation processes is widely recognised and is the subject of intense academic and industrial interest.Although the use of high pressure has been shown by physicists and geoscientists to be a powerful method for preparing new polymorphs of metals, alloys, ceramics, and minerals, it is only relatively recently that high pressure has been exploited to modify intermolecular interactions in simple molecular compounds.Thus it has been shown that new polymorphs of simple molecular organic and inorganic compounds such as ketones, alcohols, and mineral acids are readily obtained by cooling the liquid compound contained within a diamond-anvil cell under conditions of high pressure.Spectroscopic and structural characterisation of these new polymorphs can then be performed in situ.Whilst this technique is ideally suited for studying compounds that have normal melting points near or below ambient temperature, it is less useful for compounds with higher melting points, such as pharmaceutical compounds, pigments, or explosives.The problem is exacerbated by the generally steep increase in melting point associated with increasing pressure, with the result that thermal decomposition of the compound occurs well before the onset of melting.We have overcome this problem by using a solvent so that higher melting compounds are effectively recrystallised from solution at elevated pressures, typically in the range 1-20 kbar.The technique has allowed us to extend greatly the range of compounds that may be studied and has been used successfully to identify and characterise new polymorphs of a range of organic compounds.The high-pressure recrystallisation technique also provides a route for the preparation and structural characterisation of new solvates of organic compounds, e.g. the 1:1 methanol solvate of paracetamol [1].Its potential as a new method of screening pharmaceutical compounds for polymorphism and solvate formation is currently being explored and will be reported here.

The solid-state structures of 43 Li, Na, K, Rb, Mg, Ca and Ba salts of para- and meta-sulfonated azo dyes have been examined and can be categorised into three structural classes. All form alternating organic and inorganic layers, however, the nature of the coordination network that forms these layers differs from class to class. The class of structure formed was found to be primarily governed by metal type, but can also be influenced by the nature and position of the organic substituents. Thus, for the para-sulfonated azo dyes, Mg compounds form solvent-separated ion-pair solids; Ca, Ba and Li compounds form simple coordination networks based on metal-sulfonate bonding; and Na, K and Rb compounds form more complex, higher dimensional coordination networks. Compounds of meta-sulfonated azo dyes follow a similar pattern, but here, Ca species may also form solvent-separated ion-pair solids. Significantly, this first attempt to classify such dyestuffs using the principles of supramolecular chemistry succeeds not only for the simple dyes used here as model compounds, but also for more complex molecules, similar to modern colourants.

A simultaneous experimental and computational search for polymorphs of chlorothalonil (2,4,5,6-tetrachloro-1,3-benzenedicarbonitrile) has been conducted, leading to the first characterization of forms 2 and 3. The crystal structure prediction study, using a specifically developed anisotropic atom-atom potential for chlorothalonil, gave as the global minimum in the lattice energy a structure that was readily refined against powder diffraction data to the known form 1 (P2(1)/a). The structure of form 2 was solved and refined from powder diffraction data, giving a disordered structure in the Rm (166) space group (Z = 3). It could also be refined against a P1 ordered model, starting from a low-energy hypothetical sheet structure found in the computational search. This shows that the disorder could be associated with the stacking of ordered sheets. The disordered structure for form 2 was later confirmed by single-crystal X-ray diffraction. The structure of form 3, determined from single-crystal diffraction, contains three independent molecules in the asymmetric unit in P2(1) (4) (Z = 6). Powder diffraction showed that this single-herringbone structure was similar to two low-energy structures found in the search. Further analysis confirmed that form 3 has a similar lattice energy and contains elements from both these predicted structures, which can be considered as good approximations to the form 3 structure.

We investigate the relative stabilities, in the gas and solid phases, of three tautomers of hydroxytriazine. In order to study the solid state energetics, we generate a number of hypothetical crystal structures for each tautomer, which we then subject to lattice energy minimisation. In both the solid and gas phases, we find that hydroxytriazine (TOH) and the ortho-protonated triazinone tautomer (T1) are almost indistinguishable in energy and are significantly more stable than the para-protonated triazinone tautomer (T2). In the crystal structures, both the experimental ones of related molecules and the hypothetical ones generated for hydroxytriazine and its triazinone tautomers, we find the expected hydrogen bonding interactions. In addition, various motifs associated with pi-stacking are often found in the experimental structures.

Three model 2,4,6-tris(amino)-1,3, 5-triazines, structurally related to a dyestuff molecule previously studied by NMR, were synthesized in order to enable the effects of rotamer exchange on the NMR spectra to be investigated in more detail. Two of the compounds are novel. Internal rotation of the triazine ring substituents was studied by variable-temperature solution-state H-1, C-13 and N-15 NMR spectroscopy. All the expected rotamers were detected for each molecule. Rotamer exchange rates varied from slow to fast over the temperature range -40 to 90degreesC, as observed for the dyestuff molecule itself. Solid-state C-13 and N-15 NMR provided information about the structures of the solid molecules. A full crystal structure determination from high-resolution powder x-ray diffraction was achieved for one of the molecules using simulated annealing techniques. Ab initio MO and N-15 NMR chemical shift calculations, based on energy-minimized structures derived from the x-ray structure determination, enabled the effect of intermolecular hydrogen bonding on the N-15 NMR chemical shifts to be studied. The results compared favourably with the experimental solid-state N-15 NMR shifts. Copyright (C) 2003 John Wiley Sons, Ltd.

Oxidation of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD, 1 a) and N,N'-diphenyl-N,N'-bis(2,4-dimethylphenyl)-(1,1'-biphenyl)-4,4'-diamine (1 b) with SbCl(5) affords the corresponding radical cations quantitatively. The crystal and molecular structure of 1 b and [1 b]SbCl(6), the first tetraphenyl benzidene derivatives to be characterised crystallographically in both the neutral and radical cation states, reveal molecular parameters in agreement with the predictions made on the basis of DFT studies. Analysis of the NIR transition in the radical cations [1](+) (.) allows an estimate of the electronic coupling parameter V (1 a(+) (.) 3200 cm(-1); 1 b(+) (.) 3300 cm(-1)), the reorganisation energy lambda(1 a(+) (.) 7500 cm(-1); 1 b(+) (.) 7800 cm(-1)), and the linear coupling constant l (1 a(+) (.) 3100 cm(-1); 1 b(+) (.) 2700 cm(-1)) of the symmetric mode.

Molecular modelling computation using the gaussian 94 package of programs was carried out to estimate four different barriers to internal rotation about amine nitrogen to sp2 carbon bonds for two compounds with triazine rings. Whereas two of the processes appear to retain a planar side-chain nitrogen environment throughout the internal rotation, the other two involve pyramidalisation. In the latter two cases, after the barrier is passed, the process may or may not include a transient inversion at nitrogen. The internal rotation for cyclotriazine systems is discussed in relation to those for aniline and formamide. The four barrier magnitudes calculated for the triazines are in the same order as (though somewhat larger than) those measured by variable-temperature NMR bandshape analysis for a relevant compound.

When determining crystal structures of organic molecular materials from high-resolution powder diffraction data, the key step is the generation of reliable trial structures fur final refinement. The subject of the study reported here is the pharmaceutical material anhydrous theophylline (3,7-dihydro-1,3-dimethyl- 1H-purine-2,6-dione), which contains both oxygen and nitrogen as possible hydrogen bond acceptor atoms. A systematic search of direct space was employed to assess every possible packing arrangement of the asymmetric unit within the experimentally determined unit cell. Trial structures were ranked in terms of calculated lattice energy and weighted residuals from a comparison of calculated and experimental X-ray diffraction profiles. The systematic search found two packing arrangements with different intermolecular hydrogen-bonding motifs within the same unit cell. In one, denoted NH. . . N, the amino hydrogen is hydrogen bonded to the aldimine nitrogen, and in the other, denoted (NHO)-O-. . ., to the carbonyl oxygen neighboring the imidazole ring. These trial structures were "virtually indistinguishable" in terms of calculated lattice energy or X-ray profile fit. Solid-state NMR spectra of a commercial sample not only confirmed immediately that there was only one molecule in the crystallographic asymmetric unit but also produced distinctive C-13 and N-15 chemical shifts. The experimentally determined N-15 chemical shifts showed considerably better agreement with values from ab initio calculations for the trial crystal structure with N--H N hydrogen bonding. In these calculations, representative chains of three hydrogen-bonded molecules were employed as models for the (NHN)-N-. . . and (NHO)-O-. . . trial crystal structures. In addition, a more sophisticated analysis of the lattice energy hypersurfaccs. using a distributed multipole based intermolecular potential, indicated that the N-(HN)-N-. . . trial structure is the more stable. It was noted that the NH N packing motif identified by our studies is observed in a single-crystal determination for theophylline reported independently while our investigations were ongoing. Our study shows how the potential for polymorphism in a "given unit cell'' may be assessed successfully by combining several complementary experimental and theoretical approaches.

Proton and C-13 solution-state spectra were obtained for a substituted triazine and assignments made for the signals using different solvents. Site-exchange effects were observed in H-1 spectra at different temperatures below ambient for a CD3OD solution. The bandshapes were fitted for three-site exchange and the relevant rate constants extracted. The exchange was attributed to internal rotation of the substituents about the triazine ring. Activation parameters were calculated: for exchange between one pair of sites Delta H-double dagger = 71 +/- 4 kJ mol(-1) and Delta S-double dagger = 33 +/- 15 J mol(-1) K-1, and for a second pair Delta H-double dagger = 72 +/- 5 kJ mol(-1) and Delta S-double dagger = 39 +/- 26J mol(-1) K-1, whereas direct exchange between the remaining pair of sites is negligible. Exchange involving a fourth rotamer affects the spectra at lower temperatures, which assists in a partial assignment of the observed peaks to the rotamers. These results are discussed in relation to molecular modelling information and literature values. Solution-state and solid-state C-13 spectra were also recorded but the latter are broad, making detailed assignment difficult. Copyright (C) 2000 John Wiley & Sons, Ltd.

Phosphorus-31 and carbon-13 CPMAS NMR spectra have been obtained for imino(triphenyl)phosphorane and amino(triphenyl)phosphonium bromide. Detailed analysis yields information about the P-31 shielding tensor and the N-14 quadrupole coupling tensor. The static P-31 spectrum of the bromide was also analysed in terms of the relevant tensors. Ab initio calculations at the hf/6-31g* level reproduce the observed data well, except for the isotropic shifts, which require a larger basis set and/or higher level of theory. The orientations of the tensors in the molecular frame are derived for the bromide from the calculations.

nBu3SnF and Mes3SnF (Mes = mesityl) are organotin fluorides that have direct Sn–F bonds. The119Sn and19F NMR spectra of these compounds have been measured using a selection of CPMAS probes. Doubly decoupled {1H,19F} as well as singly decoupled {1H}119Sn NMR spectra are shown. Double decoupling gives higher resolution spectra and allows the sample of Mes3SnF to be spun slower to give more spinning-sidebands without overlapping of signals, giving improved analysis. The doubly decoupled spectra are sensitive to the power and offset of the decouplers. The effect of off-resonance decoupling has been observed for119Sn NMR through reduced splittings when the19F decoupler power and offset were varied. Proton-decoupled19F spectra have been measured using a new HF double-resonance probe. In addition, two-dimensional heteronuclear correlation spectra are presented for Mes3SnF, allowing a full assignment for the19F and119Sn chemical shifts of the two sites. Full shielding tensor data are reported for both compounds. Values have been derived for the effective (119Sn,19F) dipolar coupling constants from both119Sn and19F experiments, yielding estimates of coupling anisotropy.

The reaction of [Ru(tpy)Cl3] with the potentially cyclometallating ligand 2,2′:6′,4″-terpyridine (HL) results in the formation of the non-metallated complex ion [Ru(tpy)(HL)Cl]+ and the complex ion [Ru(tpy)(LH)]2+ in which the cyclometallated ligand L is protonated on the non-coordinated nitrogen atom. If ethane-1,2-diol is used as the solvent the latter complex is the major product, while the use of glacial acetic acid favours the former. This electron-withdrawing pyridinium functionality significantly affects the properties of the complex. In contrast, the non-metallated complex behaves like similar ruthenium complexes with N5Cl donor sets. Both complexes have been fully characterized as their hexafluorophosphate salts, and studied by cyclic voltammetry and electronic spectroscopy. The complex [Ru(tpy)(LH)][PF6]2 is weakly luminescent at room temperature in acetonitrile solution.