The sterically demanding carbene 1,3-di-tert-butylimidazolidin-2-ylidene and B(C(6)F(5))(3) form a "frustrated" Lewis pair (FLP), which is able to cleave dihydrogen heterolytically. In the absence of reactants, this FLP system exhibits dehydrogenation reactivity to give a mixture of an imidazolidinium borate and an abnormal carbene-borane adduct.

We have redetermined the known structures of (i) methylthiourea (MTU) and (ii) 1,1-dimethylthiourea (1,1-DMTU), and investigated the structure of 1,3-dimethylthiourea (1,3-DMTU), which was however severely disordered. We report the structures of crystalline adducts of (iii) MTU with morpholine (1:1), (iv) 1,1-DMTU with 1,4-dioxane (2:1) and (v) 1,3-DMTU with 1,4-dioxane (2:1). Finally, (vi) we determined the structure of tetramethylthiourea (TetMTU). (i) In both independent molecules of MTU, the methyl group is trans to the C=S group across the C-N bond. The two molecules are connected to form an R2(2)(8) dimer by mutual N-H...S=C interactions. The packing involves six N-H...S=C interactions and is three-dimensional. (ii) The packing of the MTU-morpholine adduct is a layer structure, within which both molecules form linear aggregates parallel to the b axis. (iii) The packing of 1,1-DMTU involves N-H...S=C hydrogen bonds forming a corrugated layer structure. (iv) In the 2:1 adduct between 1,1-DMTU and 1,4-dioxane, the DMTU molecule occupies a general position whereas the dioxane molecule lies across an inversion centre. The crystal packing involves chains of alternating 1,1-DMTU R2(2)(8) dimers and dioxanes, both across inversion centres. (v) In the 2:1 adduct between 1,3-DMTU and dioxane, the 1,3-DMTU molecule occupies a general position, while the dioxane molecule lies across an inversion centre. One methyl group of the DMTU is trans and one cis to the sulfur across the corresponding C-N bond. The molecules form chains of alternating 1,3-DMTU R2(2)(8) dimers and dioxanes, both across inversion centres. Crystals of the 2:1 adduct between 1,3-DMTU and morpholine were also obtained, and were isotypic with the dioxane adduct. The morpholine molecule is disordered across the inversion centre. (vi) The molecule of TetMTU displays crystallographic twofold symmetry. Significant distortions reflect the steric pressure between methyl groups trans to sulfur. The packing of TetMTU involves only a weak hydrogen bond, C-Hmethyl...S, which connects the molecules to form layers.

The monoselenide of 1,8-bis(diphenylphosphino)naphthalene reacts with (tht)AuCl to give the gold(III) system [(dppnAuSe)(2)](2+) 2Cl(-) (1); bromination of the bromogold(I) complex of the 1,2-bis(diphenylphosphino)methane monosulfide ligand furnishes the tribromide salt (2a) of a gold(III) cation [LAuBr(2)](+); bromination of the bromogold(I) complex of the 1,2-bis(diphenylphosphino)benzene monosulfide ligand leads to a mixed bromide/tetrabromoaurate salt (3) of a heterocyclic dication involving a [-PPh(2)-S-PPh(2)-](2+) moiety; analogous reactions of triphenylphosphine sulfide and selenide complexes lead to tetrabromoaurate salts (4a and 4b) of the (bromochalcogeno)phosphonium cations Ph(3)PEBr(+).

Trimethylthiourea crystallizes in two different polymorphic modifications. Polymorph I crystallizes in the monoclinic space group P21/c with Z = 8, whereas polymorph II crystallizes in the alternative setting of the same space group, P21/n with Z = 4. Both polymorphs form chains of molecules linked by hydrogen bonds N–H···SC via glide planes, with translational repeats after four molecules (the two independent molecules alternate) or two molecules, respectively. Interplanar angles between molecules in the chain differ appreciably between I and II, and for I, one hydrogen bond is very nonplanar with respect to the N2CS acceptor plane. Solvent-mediated conversion experiments prove that polymorph II is the thermodynamically stable polymorph at room temperature, where I is metastable, and that I can be obtained by solidification of the melt. On heating, I transforms slowly into II with no detectable transfer of energy, and on further heating, melting of this polymorph is observed. DSC experiments reveal that I exhibits the higher melting point and the lower heat of fusion, and therefore, the polymorphs are related by enantiotropy, with I being stable at higher temperatures. Isothermic DSC experiments prove that the thermodynamic transition point is between 70 and 80 °C, in agreement with the value calculated from the melting enthalpy and the melting point of both polymorphs. Further experiments reveal that at very low heating rates II initially melts and that I crystallizes from the liquid and melts on further heating. This process can only be observed if crystals of polymorph I are present during melting of II, in order to induce crystallization of polymorph I.

The solvents 1,4-dioxane and morpholine have been employed to synthesize solvates of urea and thiourea.The structures confirm the tendency of urea to form more rigid systems of hydrogen bonds in the plane of the N 2 CLO moiety, thus forming layer structures with close complementarity of the donors and acceptors, whereas the more flexible sulfur acceptor of thiourea can also accept hydrogen bonds from donors that lie far from the N 2 CLS plane, forming three-dimensional packing patterns with much more variable parameters. A database investigation confirms these tendencies. The solvate urea : morpholine (1 : 1) crystallizes in Pbcm with Z = 4. The complete urea molecule lies in the mirror plane, as do the heteroatoms of the morpholine molecule. The molecular packing is a layer structure. The solvate urea : 1,4-dioxane (1 : 1) crystallizes in P2/c with Z = 2. The CLO bond of the urea molecule lies along a twofold axis, whereas the dioxane molecule lies across an inversion centre. The molecules form a layer structure analogous to that of the morpholine solvate. The thiourea solvates are more complex, and both involve a more irregular hydrogen bonding geometry at sulfur. The solvate thiourea : morpholine (4 : 3) crystallizes in P2 1 /c with Z = 2. The asymmetric unit contains two independent molecules of thiourea, one morpholine on a general position, and one morpholine disordered over an inversion centre. The thiourea molecules combine to form an open framework with a series of channels, in which the morpholine molecules are attached. The solvate thiourea : 1,4-dioxane (4 : 1) crystallizes in P2 1 /n with Z = 2. The asymmetric unit contains two independent molecules of thiourea and one molecule of dioxane across an inversion centre. One thiourea molecule and the dioxane combine to form a layer structure. The second thiourea molecule links these layers in the third dimension.