High-Pressure Transformations and the Resonance Structure of Thiourea

Abstract

High pressure increases intermolecular interactions in the crystal environment and affects the molecular dimensions of thiourea, CS(NH 2 ) 2 , consistently with changing contributions of the thione and zwitterionic mesomers. The ambient-pressure phase V (space-group Pnma, Z = 4) at 0.34 GPa transforms to phase VI, of the same spacegroup symmetry, but with the larger unit-cell trifold (Z = 12). Another pressure-induced transition to phase VII was previously postulated for thiourea at 0.54 GPa; however, no associated structural transformations were identified. Our high-pressure single-crystal X-ray diffraction study reveals that following the transition at 0.34 GPa the lattice parameters and crystal structure strongly and monotonically change to about 0.65 GPa while the crystal symmetry is retained.

High-pressure and environment effects in selenourea and its labile crystal field around molecules

“…This crystal (Fig. 5) is isostructural with the analogous thiourea duotritohydrate, 3SC(NH 2 ) 2 Á2H 2 O (Tomkowiak & Katrusiak, 2018). Both 3SeC(NH 2 ) 2 Á2H 2 O and 3SC(NH 2 ) 2 Á2H 2 O decompose on releasing pressure and our attempts to recover these crystals to ambient conditions failed.…”

“…For example, in ethynylbenzene (Dziubek et al, 2007) the Z 0 number increases from 2.5 to 3; in pyrazine (Patyk et al, 2015) from 0.25 to 0.5; in chlorpropamide (Seryotkin et al, 2013) from 1 to 2. Likewise, in thiourea (Tomkowiak & Katrusiak, 2018) Z 0 in the ambient-pressure phase V is equal to 1 and in high-pressure phase VI the Z 0 ISSN 2052-5206 number increases to 3; the urea (Olejniczak et al, 2009;Roszak & Katrusiak, 2017) crystal transforms from the ambient-pressure phase I (Z 0 = 0.25) to phase III (Z 0 = 1) at 0.48 GPa.…”

High-pressure preference for reduced water content in porous zinc aspartate hydrates

“…For example, the hydrate Y 2 (C 2 O 4 ) 3 Á10H 2 O reduces its water content at 1 GPa to Y 2 (C 2 O 4 ) 3 Á6H 2 O (Zakharov et al, 2017), the dehydration of phosphatidylinositol bilayers was postulated above 0.7 GPa based on IR spectroscopy (Carrier & Wong, 1996), and the decomposition of orthoboric acid with the release of water at about 2 GPa was reported by Kuznetsov et al (2006). We also noted that pressures above 1 GPa prevent the formation of hydrates of thiourea (Figuiere et al, 1975;Tomkowiak et al, 2013;Tomkowiak & Katrusiak, 2018) and at pressures above 8 GPa no methane hydrates are formed (Kevenvolden, 1995). Presently, we have established that the porous crystals of ZnAsp 2 ÁnH 2 O display structural features connected to their water content.…”

“…The effect of high pressure on the hydration of various organic compounds, such as methane (Kevenvolden, 1995), thiourea (Figuiere et al, 1975;Tomkowiak et al, 2013;Tomkowiak & Katrusiak, 2018), 1,4-diazabicyclo[2.2.2]octane hydroiodide (dabcoHI, Olejniczak & Katrusiak, 2010), 1,4diazabicyclo[2.2.2]octane dibromide (dabco2HBr, Andrzejewski et al, 2011), 5,6-dimethylbenzimidazole (Zieliń ski & and 4,4 0 -bipyridinium perchlorate (Anioła & Katrusiak, 2017), and minerals (Van Valkenburg et al, 1971), is well documented in the literature. However, in most cases high pressure increases the water content in a crystal structure, and exceptions are rare.…”

Lab in a DAC – high-pressure crystal chemistry in a diamond-anvil cell

“…So far, there are numerous cases of both increased and decreased Z 0 . The Z 0 increasing with pressure was observed, for example, in ethynylbenzene (Dziubek et al, 2007), pyrazine (Patyk et al, 2015), chlorpropamide (Seryotkin et al, 2013), thiourea (Tomkowiak & Katrusiak, 2018), isopropyl alcohol and urea when phase I transforms to phase III (Olejniczak et al, 2009;Roszak & Katrusiak, 2017). In another group of compounds the Z 0 number decreases in the highpressure phase, for example in 6-chloro-4,4,5,7-tetramethyldihydrocoumarin (Rajewski et al, 2018), 3-hydroxy-4,5-dimethyl-1-phenylpyridazin-6-one (Roszak et al, 2016) and bromochlorofluoroacetic acid (Gajda et al, 2009).…”