Louise S. Price

Towards crystal structure prediction of complex organic compounds – a report on the fifth blind test

The results of the fifth blind test of crystal structure prediction, which show important success with more challenging large and flexible molecules, are presented and discussed.

Report on the sixth blind test of organic crystal structure prediction methods

The results of the sixth blind test of organic crystal structure prediction methods are presented and discussed, highlighting progress for salts, hydrates and bulky flexible molecules, as well as on-going challenges.

A strategy for producing predicted polymorphs: catemeric carbamazepine form V.

A computationally assisted approach has enabled the first catemeric polymorph of carbamazepine (form V) to be selectively formed by templating the growth of carbamazepine from the vapour phase onto the surface of a crystal of dihydrocarbamazepine form II.

Organotin unsymmetric dithiocarbamates: synthesis, formation and characterisation of tin(II) sulfide films by atmospheric pressure chemical vapour deposition

A series of tin unsymmetric dithiocarbamate complexes have been made from metathesis reaction of [CH3(C4H9)NSC2]Li and RnSnCl4-n; [RnSn(S2CN(C4H9)CH3)(4-n)] [n = 3, R = Me (1), Bu (2), Ph (3); n = 2, R = Me (4), Bu (5), Ph (6); n = 1, R = Me (7), Bu (8), Ph (9)]. The complexes were characterised by microanalysis, C-13, H-1 and Sn-119 NMR, Mossbauer and, in the case of 3, by X-ray diffraction, which revealed one short Sn-S [2.4631(9) Angstrom] and one long Sn-S interaction [3.084(l) Angstrom] indicative of a weakly chelating dithiocarbamate ligand. Atmospheric pressure chemical vapour deposition using I and 8 with H2S at 350-550 degreesC produced SnS and Sn2S3 films on glass substrates. The tin sulfides were analysed by Raman, EDAX, SEM and band gap measurements. Growth rates were of the order of 150 nm min(-1)

Deposition of tin sulfide thin films from tin(IV) thiolate precursors

AACVD (aerosol-assisted chemical vapour deposition) using (PhS)(4)Sn as precursor leads to the deposition of Sn3O4 in the absence of H2S and tin sulfides when H2S is used as co-reactant. At 450 degreesC the film deposited consists of mainly SnS2 while at 500 degreesC SnS is the dominant component. The mechanism of decomposition of (PhS)(4)Sn is discussed and the structure of the precursor presented.

Deposition of tin sulfide thin films from novel, volatile (fluoroalkythiolato)tin(IV) precursors

Novel, volatile (fluoroalkylthiolato)tin(IV) precursors have been synthesised and (CF3CH2S)4Sn used to deposit tin sulfide films under APCVD (atmospheric pressure chemical vapour deposition) conditions. H2S is, however, required as co-reactant. Films deposited at 300–400 °C are composed of sulfur-deficient SnS2, films deposited at 450 and 500 °C comprise the sesquisulfide, Sn2S3, and the films deposited at 550 or 600 °C are sulfur-deficient SnS. The structure of [CF3(CF2)5CH2CH2S]4Sn is also reported.

The observed and energetically feasible crystal structures of 5-substituted uracils

A search of the Cambridge Structural Database for crystal structures of 5-substituted uracils shows that, although there is a recurrent motif with symmetric hydrogen bonding and interdigitation of the 5-substituent R, a range of other hydrogen bonded ribbons, sheets and three-dimensional motifs are possible. In order to try and rationalize this, we have performed a combination of experimental studies and computational searches for low energy structures for the 12 simple 5-substituted uracils with R = H, CH3, CH2CH3, CHCH2, CN, OH, NH2, NO2, F, Cl, Br and I. Crystallization experiments on these compounds yielded the first single crystal X-ray determinations of 5-ethyluracil and 5-cyanouracil, as well as low temperature redeterminations of the disordered structures of 5-chlorouracil and 5-bromouracil. The lattice energies were calculated for the known crystal structures and compared with the computed lattice energy landscape for each molecule (except R = Br and I). Although the symmetric ribbon motif often dominates the computed crystal energy landscape, all of the molecules show a variety of different hydrogen bonding structures within a small energy range (5 kJ mol−1) of the global minimum and exhibit quite a diverse range of energetically competitive motifs. Thus, the range of crystallization outcomes, from polymorphism and other multiple forms, to the difficulty in growing single crystals (R = CHCH2 and NH2) probably reflects the sensitivity of the various hydrogen bonding motifs to the substituent and limited range of crystallization conditions that can be applied.

Synthesis and thermal decomposition studies of homo- and heteroleptic tin(IV) thiolates and dithiocarbamates: molecular precursors for tin sulfides

The syntheses and X-ray structures of novel heteroleptic thiolate/dithiocarbamate derivatives (Et2NCS2)2(RS)2Sn (R = Cy, CH2CF3) have been examined and their thermal decompositions compared with those of selected tin(II) and tin(IV) dithiocarbamates. The heteroleptic species decompose to SnS by initial elimination of RSSR to afford (Et2NCS2)2Sn and subsequent loss of [Et2NC(S)]2S. In contrast, (Et2NCS2)4Sn decomposes via [(Et2NCS2)2SnS]2, whose structure has been determined, and finally to SnS2 by sequential elimination of [Et2NC(S)]2S. The two families of compounds, (R2NCS2)4Sn and (Et2NCS2)2(RS)2Sn, thus provide single-source materials for bulk SnS2 and SnS, respectively, by virtue of their differing decomposition pathways. Preliminary CVD experiments with (Et2NCS2)2(CyS)2Sn are also reported.

Atmospheric Pressure CVD of SnS and SnS2 on Glass

The atmospheric pressure chemical vapor deposition (APCVD) of SnS and SnS2 films from the reaction of SnCl4 and H2S was studied. The APCVD reaction of SnCl4 and H2S produced fast growth rates of good quality chlorine-free crystalline SnS films. SnS films were formed at 545 °C, while SnS2 films were produced at lower temperatures.

Designing precursors for the deposition of tin sulphide thin films

This paper reviews the work carried out by the authors over the last three years on the deposition of tin sulphide films. Particular emphasis is placed on the design and limitations of single-source precursors for these films. Simple homoleptic thiolates Sn(SR)(4) only generate tin sulphides in combination with H2S, otherwise Sn3O4 is produced by in situ formation of Sn(0) and subsequent oxidation. This problem is overcome by the use of chelating dithiolates. The decomposition of mixed ligand (RS)(2)Sn(S2CNEt2)(2) are also described, as are the synthesis and structures of mixed metal thiolates (Ph3PP)AuSSnCy3 and PhHgSSnCy3, potential precursors for ternary tin-containing sulphides.