Methylthioureas and their morpholine and dioxane adducts; hydrogen-bonding patterns

Crystal structure of the 1:2 adduct of bis-(piperidinium) sulfate and 1,3-di-methyl-thio-urea

In the title compound, 2C5H12N+·SO42-·2C3H8N2S, the C=S groups of the two independent 1,3-di-methyl-urea mol-ecules and the sulfur atom of the anion lie on twofold axes. The packing is centred on bis-(piperidinium) sulfate ribbons parallel to the c axis; the cations are hydrogen bonded to the sulfate by N-H⋯O and C-H⋯O inter-actions. The 1,3-di-methyl-urea mol-ecules are also hydrogen bonded to sulfate O atoms, and project outwards from the ribbon parallel to the b axis.

Structure of the adducts methylthiourea: 1,4-dioxane (2:1) and 1,1-dimethylthiourea: morpholine (1:1)

The adducts methylthiourea:1,4-dioxane (2:1) (1) and 1,1-dimethylthiourea:morpholine (1:1) (2) were prepared and their crystal structures determined. In 1, hydrogen bonding involving the methylthiourea molecules leads to the formation of R 2 2 ( 8 ) ${\rm{R}}_2^2(8)$ rings and thence to molecular ribbons parallel to [110]. The dioxane molecules accept hydrogen bonds from the remaining NH groups, and their inversion symmetry means that they connect adjacent methylthiourea ribbons, forming a layer structure parallel to (11̅1). In the packing of 2, dimethylthiourea dimers cannot link to each other because of the blocking effect of their methyl groups, but instead are linked indirectly via morpholine molecules, the NH groups of which are simultaneously hydrogen bond acceptors from the remaining NH function of dimethylthiourea and donors towards the sulfur atom of a neighbouring dimer. The overall effect is to form broad ribbons parallel to the a axis, with the morpholine molecules occupying the peripheral positions. The morpholine oxygen atom of 2 is not involved in classical hydrogen bonds.

Structural Characterization of Thermochromic and Spin Equilibria in Solid-State Ni(detu)4Cl2 (detu = N,N'-Diethylthiourea)

Consecutive thermochromic lattice distortional and spin crossover equilibria in solid-state Ni(detu)4Cl2 (detu = N,N'-diethylthiourea) are investigated by variable-temperature X-ray crystallography (173-333 K), DFT calculations, and differential scanning calorimetry. Thermochromism and anomalous magnetism were reported previously (S. L. Holt, Jr., et al. J. Am. Chem. Soc. 1964, 86, 519-520); the latter was attributed to equilibration of a singlet ground state and a thermally accessible triplet state, but structural data were not obtained. A crystal structure at 173(2) K revealed [Ni(detu)4](2+) centers with distorted planar ligation of nickel(II) to the four sulfur atoms, with an average Ni-S bond length of 2.226(3) Å. The nickel ion was displaced out-of-plane by 0.334 Å toward a proximal apical chloride at a nonbonding distance of 3.134(1) Å. Asymmetry in the trans S-Ni-S angles was coupled to a monoclinic ↔ tetragonal lattice distortion (T(1/2) = 254 ± 11 K), resulting in thermochromism. Spin crossover occurs by tetragonal modulation of nickel(II) with approach of the proximal chloride at higher temperatures (T(1/2) = 383 ± 18 K), which is consistent with a contraction of -0.096(4) Å in the Ni···Cl separation observed at 293 K. A high-spin (S = 1) square-pyramidal [Ni(dmtu)4Cl](+) model (dmtu = N,N'-dimethylthiourea) was optimized by DFT calculations, which estimated limiting equatorial Ni-S bond lengths of 2.45 Å and an apical Ni-Cl bond of 2.43 Å. Electronic spectra of the spin isomers were calculated by TD-DFT methods. Assignment of the FTIR spectrum was assisted by frequency calculations and isotope substitution.

Two polymorphs of 4-hydroxypiperidine with different NH configurations

4-Hydroxypiperidine 1 exists in two crystal forms, tetragonal 1t with axial NH and orthorhombic 1o with equatorial NH.

Imidazolidin-2-one: pseudosymmetry and twinning

The title compound, C3H6N2O, crystallizes with imposed twofold symmetry in the space group I4(1)/a. The five-membered ring displays a half-chair conformation. N-H···O hydrogen bonds connect the molecules to form R2(2)(8) rings and thence ribbons parallel to the a and b axes. These intersect via O2H2 rings involving longer H···O contacts. The crystal was merohedrally twinned. Preliminary indications of the higher symmetry space group I4(1)/amd, which would require the ring to be planar, proved to be incorrect. A previous brief report of the structure in Fdd2 is also probably incorrect.