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Ambient‐pressure trigonal phase α of selenourea SeC(NH2)2 is noncentrosymmetric, with high Z′ = 9. Under high pressure it undergoes several intriguing transformations, depending on the pressure‐transmitting medium and the compression or recrystallization process. In glycerine or oil, α‐SeC(NH2)2 transforms into phase β at 0.21 GPa; however in water, phase α initially increases its volume and can be compressed to 0.30 GPa due to the formation of α‐SeC(NH2)2·xH2O. The single crystals of α‐SeC(NH2)2 and of its partial hydrate α‐SeC(NH2)2·xH2O are shattered by pressure‐induced transitions. Single crystals of phase β‐SeC(NH2)2 were in situ grown in a diamond‐anvil cell and studied by X‐ray diffraction. The monoclinic phase β is centrosymmetric, with Z′ = 2. It is stable to 3.20 GPa at least, but it cannot be recovered at ambient conditions due to strongly strained NH...Se hydrogen bonds. No hydrogen‐bonding motifs present in the urea structures have been found in selenourea phases α and β. [ABSTRACT FROM AUTHOR]

High‐nitrogen‐content compounds 6‐azido‐1,2,4‐triazolo[4,3‐b]pyridazine (C5H3N7) and its 3‐methyl derivative (C6H5N7) have been in situ crystallized in a diamond‐anvil cell and their structures determined by single‐crystal X‐ray diffraction. Under ambient and high‐pressure conditions the crystallizations yield the same phases: the C5H3N7 anhydrate and C6H5N7 hydrated clathrate. In both the structures there are clearly distinguished regions of short CH...N and N...N intermolecular contacts, the latter involving exclusively the azide groups. High pressure initially increases the contents of water in the channel pores of the clathrate. [ABSTRACT FROM AUTHOR]

Reports on the third polymorph (MH3) of maleic hydrazide, studied by X-ray diffraction and shown to be monoclinic, space group P2[sub 1]/n. Finding that the polymorph MH3 is the prevailing form along with the rare triclinic polymorph MH1; Accommodation of the supramolecular conformations to the requirements of close pacing of the aggregates in crystal lattices.

Abstract: Intermolecular interactions in a synthesized C-acid, 4-nitrophenyl[bis(ethylsulfonyl)]methane have been analysed and its structure determined by X-ray diffraction. The molecular packing in the crystal is governed by CH…O. The dimensions of the hydrogen bonds and the shortest non-bonded distances are also determined. The possible implications in the formation of the hydrogen bonded complexes with the strong organic bases are also discussed. [Copyright &y& Elsevier]

Abstract: The 2:2 hydrogen-bonded complex between Kemp’s triacid (KTA) and 1,1,3,3-tetramethylguanidine (TMG) has been synthesised and studied by X-ray diffraction and by FT-IR spectroscopy. Cocrystals of KTA–TMG belong to the monoclinic system and crystallize in the space group is P2 1 with a =10.5017(3)Å, b =7.9504(3)Å, c =11.8910(4)Å, β =104.004(4)° and Z =2. The ring of the KTA monoanion molecule exhibits a chair conformation with all three carboxylic groups in the axial positions and all three methyl groups in the equatorial positions. In the crystal of the complex, cooperative systems involving inter- and intra-molecular hydrogen bonds are formed. In the solid state two protonated TMG molecules and two deprotonated KTA molecules form a dimer in which three-dimensional hydrogen-bonded networks are found. [Copyright &y& Elsevier]