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Reversible temperature-mediated solid phase changes, otherwise known as enantiotropic transformations, occur in many molecular crystals. These transformations take place as a result of the free-energy stabilization through entropic contributions at finite temperatures and can often have significant implications for the properties of crystalline solids. As such, understanding and predicting these transformations is of great importance. In this study, we utilize molecular simulations to elucidate the mechanism behind the enantiotropic layer-slip phase transformation between the orthorhombic and monoclinic versions of paracetamol form III (form III-m and III-o). Using standard molecular dynamics (MD) in addition to crystal adiabatic free-energy dynamics, an MD-based enhanced sampling approach for crystalline systems, we demonstrate that the transformation from the monoclinic form III-m to the orthorhombic form III-o is driven by localized and dynamic disorder within the structure rather than a perfect crystal-to-crystal transition. These results suggest that the orthorhombic form III-o structure does not exist as a perfect orthorhombic crystal with fully aligned layers, but rather, as an entropy-stabilized collective ensemble average of various misaligned layer-slipped structures. Overall, these simulation approaches, which explicitly treat dynamic structural disorder, allowed us to map out the free-energy landscape of this enantiotropic transformation as a function of temperature and extract critical insights into the underlying mechanism of the transformation.

Benzamide, a simple derivative of benzoic acid and a common intermediate of pharmaceutical compounds, was reported to form two polymorphs in 1832, but the single crystal structure of the more stable form was not solved until 1959. Nearly 50 years later, the second form was characterized by powder diffraction, followed shortly thereafter by characterization of a third form, a polytype of the most thermodynamically stable Form I. These two new forms, Forms IIand III, are metastable. Herein, we describe a fourth polymorph, Form IV, discovered by melt crystallization concurrently with its crystallization under confinement at small length scales (<10 nm), where it is stable indefinitely. Form IIIexists under confinement in larger pores, and melting point data for different pore sizes corroborate the existence of Form IVbelow 10 nm. Form IVis highly disordered, precluding indexing of powder diffraction data other than hk0 reflections. Nonetheless, a combination of powder X-ray diffraction and computational crystal structure prediction reveals that Form IVcontains a 2D motif resembling that of Form II, but with long-range order in the third dimension masked by ubiquitous stacking faults. This approach relies on distilling a large number of candidate structures to a few possible disorder models based on benzamide tetrads that organize in 2D parquet-like tiles, with organization along the third dimension, that can be modeled with various stacking fault configurations having distinct intermolecular interactions and translations in the dimension orthogonal to the tiling planes. These observations reveal a bewildering crystallographic complexity for such a simple molecule. Nonetheless, the approach described herein demonstrates that challenging structures that may be abandoned prematurely because of poor crystallinity, twinning, or disorder can be solved.

Trimorphic paracetamol, one of the most commonly used analgesic and antipyretic drugs, has been a model system for studying transformations among phases of molecular crystalline materials. During crystallization from the melt and the glass above 0 °C, three new polymorphs of paracetamol (N-acetyl-para-aminophenol or acetaminophen) were discovered, doubling the number of known ambient forms. The crystal structure of one new form was solved using a combination of powder X-ray diffraction and computational techniques. Growth kinetics became anomalous near the glass transition: as temperature decreased, growth rate increased; this rare and poorly understood phenomenon is commonly identified as the glass-to-crystal (GC) growth mode. In addition, two polymorphs displayed optical evidence of helicoidal morphologies, a characteristic of at least 25% of molecular crystals, that has been resistant to a universal explanation.

We have performed a comparison of the experimental thermal diffuse scattering (TDS) from crystalline Aspirin (form I) to that calculated from molecular dynamics (MD) simulations based on a variety of general force fields and a tailor-made force field (TMFF). A comparison is also made with Monte Carlo (MC) simulations which use a “harmonic network” approach to describe the intermolecular interactions. These comparisons were based on the hypothesis that TDS could be a useful experimental data in validation of such simulation parameter sets, especially when calculations of dynamical properties (e.g., thermodynamic free energies) from molecular crystals are concerned. Currently such a validation of force field parameters against experimental data is often limited to calculation of specific physical properties, e.g., absolute lattice energies usually at 0 K or heat capacity measurements. TDS harvested from in-house or synchrotron experiments comprises highly detailed structural information representative of the dynamical motions of the crystal lattice. Thus, TDS is a well-suited experimental data-driven means of cross validating theoretical approaches targeted at understanding dynamical properties of crystals. We found from the results of our investigation that the TMFF and COMPASS (from the commercial software “Materials Studio”) parameter sets gave the best agreement with experiment. From our homologous MC simulation analysis we are able to show that force constants associated with the molecular torsion angles are likely to be a strong contributing factor for the apparent reason why these aforementioned force fields performed better.

With most youths now using the Internet and social networking sites (SNSs), the public has become increasingly concerned about risks posed by online predators. In response, lawmakers have begun to pass laws that ban or limit sex offenders' use of the Internet and SNSs. At the time of this article, 12 states and the federal government have passed legislation attempting to restrict or ban the use of SNSs by registered sex offenders. These laws have been successfully challenged in 4 states. In this article, we discuss examples of case law that illustrate evolving trends regarding Internet and social networking site restrictions on sex offenders on supervised release, as well as those who have already completed their sentences. We also review constitutional questions and empirical evidence concerning Internet and social networking use by sex offenders. To our knowledge, this is the first paper in the psychiatric literature that addresses the evolving legal landscape in reference to sex offenders and their use of the Internet and SNSs. This article is intended to help inform forensic mental health professionals who work with sex offenders on current concerns in this rapidly evolving legal landscape. [ABSTRACT FROM AUTHOR]

Diorganotin(IV) derivatives of 4‐acyl‐5‐pyrazolones Q2SnR2[HQ = 3‐methyl‐1‐phenyl‐4‐R‐5‐pyrazolone: HQnPe, R = neopentylcarbonyl; HQiPr, R = isopropylcarbonyl; HQtBu, R = tert‐butylcarbonyl; HQCy, R = cyclohexylcarbonyl; HQCp, R = cyclopentylcarbonyl; HQEtCp, R = (ethylcyclopentyl)carbonyl] have been synthesized and characterized spectroscopically (IR, far‐IR, 1H, 13C and 119Sn NMR) and structurally (X‐ray). Steric bulkiness in the acyl fragment of HQtBuinduces partial dissociation in solution of (QtBu)2SnMe2, which exists as an equilibrium mixture of six‐ and five‐coordinate tin species. Single‐crystal X‐ray structure determinations of several representative complexes are presented. Whereas the dialkyltin(IV) complexes are always trans‐octahedral, a diphenyltin(IV) derivative exists in the solid state that has the two phenyl groups in a cisarrangement. DMol3 and CASTEP DFT studies of this unprecedented cis, and the corresponding transconfigurations, show the former to be slightly more stable, in agreement with the diffraction study. Solid‐state 119Sn cross‐polarization magic‐angle spinning NMR spectroscopic data show that the isotropic chemical shifts (δiso,mas) and chemical‐shift anisotropies/spans (Δδ/Ω) that characterize the diphenyl(IV) derivatives are markedly removed from values measured for the corresponding dimethyl and di‐n‐butyl derivatives, thereby adding further evidence for a stable cisconfiguration in the diphenyl(IV) systems. This is supported by GIPAW DFT calculation of the 119Sn isotropic shifts and chemical‐shift anisotropies/spans from fully relaxed structures by using the CASTEP code, which provides a direct link between the cisdiphenyl(IV) arrangement and the reported differences in the 119Sn NMR spectroscopic parameters.

The article discusses the court case United States v. Watson regarding use of forceful medications on mentally disabled person for restoration of their competency to stand the trials. Topics discussed include conviction of John Watson possession of a firearm and attempted destruction of an aircraft, testimony of a psychiatrist for delusional disorder of Watson, relevance of liberty interests for the case and need for a treatment plan by psychiatrist in such cases.

After vacuum dehydration, a number of hydrated trivalent lanthanoid trifluoromethanesulfonates (“triflate”, “OTf” = F3CSO3), when recrystallized from various alcohol (ROH) solutions, yield solvates Ln(OTf)3·xROH, x= 3, 5 or 6. The following have been defined crystallographically (R/Ln/x): Me/La/3;Me/Gd/6; Et/Sm/3; Et/Gd/5 iPr/Nd,Sm/3. The Me/Gd/6complex, Gd(OTf)3·6MeOH is a mononuclear/ionic form [(MeOH)6Gd(O–OTf)2](OTf), the gadolinium environment being octacoordinate, square‐antiprismatic with the O–OTf donors quasi‐trans on different faces of the coordination polyhedron; the Et/Gd/5 complex is neutral, molecular, mononuclear [(EtOH)5Gd(O–OTf)3], also with an octacoordinate, square‐antiprismatic coordination sphere, derivative of that of the methanol solvate. The remainder form one‐dimensional polymeric arrays, successive lanthanoid atoms linked by (μ‐O–OTf–O′)3triads, at either end of a tricapped trigonal prismatic array, the ROH molecules contributing the capping atoms. A (“baseline”) (re‐)determination of the “parent” Sm(OTf)3·9H2O is also recorded.

Building on previous single crystal X‐ray structure determinations for the group 1 salts of complex thiosulfate/univalent coinage metal anions previously defined for (NH4)9AgCl2(S2O3)4, NaAgS2O3·H2O and Na4[Cu(NH3)4][Cu(S2O3)2]·NH3, a wide variety of similar salts, of the form $\rm M^{1}_{a}M\rm ^{2}_{b}(X_{c}) (S_{2}O_{3})_{d}$, M1= group 1 metal cation, M2= univalent coinage metal cation (Cu, Ag), (X = univalent anion), most previously known, but some not, have been isolated and subjected to similar determinations. These have defined further members of the isotypic, tetragonal $I{\bar 4} {\rm 2}d \textrm{ }{\rm M^{1}_{9}M^{2}X_{2}(S_{2}O_{3})_{4}({\equiv}M^{1}_{9}X_{2}[M^{2}}(S{\rm SO_{3})_{4}]{\equiv}2M^{1}X}.\textrm{ } {\rm M^{1}_{7}[M^{2}}(S{\rm SO_{3})_{4}]}$series, for M1= NH4, M2= Cu, Ag, X = NO3, Cl, Br, I, together with the K/Cu/NO3complex, all containing the complex anion [M2(SSO3)4]7−with M2in an environment of $\rm {\bar 4}$symmetry, Cu, Ag‐S typically ca.2.37, 2.58Å, with quasi‐tetrahedral S‐M‐S angular environments. Further salts of the form $\rm M^{1}_{2n-1}M^{2}(S_{2}O_{3})_{n}(\cdot xH_{2}O)$, n = 1‐3, have also been defined: For n = 3, M2= Cu, M1/x = K/2.25 or 1 5/6, NH4/6, (and also for the (NH4)4Na/4H2O·MeOH adduct) the arrays take the form ${\rm M^{1}_{5}[Cu}(S{\rm SO_{3})_{3}]{\cdot}xS}$with distorted trigonal planar CuS3coordination environments, Cu‐S distances being typically 2.21Å, S‐Cu‐S ranging between 105.31(4)–129.77(4)°; the silver counterparts take the form ${\rm M^{1}_{10}[(O_{3}S}S){\rm_{2}Ag(\mu-}S{\rm SO_{3}})_{2}{\rm Ag}(S{\rm SO_{3}})_{2}]$for M1= K, NH4. For n = 2, adducts have only been defined for M2= Ag, the anions of the M1= Na, K adducts being dimeric and polymeric respectively: Na6[(O3SS)2Ag(μ‐SSO3)2Ag(SSO3)]·3H2O, K3[Ag(μ‐SSO3)2](∞|∞)·H2O; a polymeric copper(I) counterpart of the latter is found in Na5Cu(NO3)2(S2O3)2≡ 2NaNO3·Na3[Cu(μ‐SSO3)2](∞|∞). For n = 1, NaAgS2O3, the an‐ and mono‐ hydrates, exhibit a two‐dimensional polymeric complex anion in both forms but with different contributing motifs. (NH4)13Ag3(S2O3)8·2H2O takes the form (NH4)13[{(O3SS)3Ag(μ‐SSO3)}2Ag], a linearly coordinated central silver atom linking a pair of peripheral [Ag(SSO3)4]7−entities. In Na6[(O3SS)Ag(μ‐SSO3)2Ag(SSO3)]·3H2O, the binuclear anions present as Ag2S4sheets, the associated oxygen atoms being disposed to one side, thus sandwiching layers of sodium ions; the remarkable complex Na5[Ag3(S2O3)4](∞|∞)·H2O is a variant, in which one sodium atom is transformed into silver, linking the binuclear species into a one‐dimensional polymer. In (NH4)8[Cu2(S2O3)5]·2H2O a binuclear anion of the form [(O3SS)2Cu(μ‐S.SO3)Cu(SSO3)2]8−is found; the complex (NH4)11Cu(S2O3)6is 2(NH4)2(S2O3)·(NH4)7[Cu(SSO3)4]. A novel new hydrate of sodium thiosulfate is described, 4Na4S2O3·5H2O, largely describable as sheets of the salt, shrouded in water molecules to either side, together with a redetermination of the structure of 3K2S2O3·H2O.

Theoretical crystal structure prediction (CSP) calculations of molecular crystals often generate structures representative of the components associated with disorder, stacking faults, and polytypism. The powder X-ray diffraction (PXRD) pattern of benzamide II contains diffuse scattering consistent with a disordered structure. Previous attempts to elucidate its ordered structure by PXRD and CSP were incomplete because the average structure is actually a complex superposition of multiple polytypes, thus making structure determination particularly challenging. To address this problem, an approach to modeling such complex structures from PXRD data and CSP in combination with molecular dynamics simulations is proposed. Using this approach, the potential building blocks for polytypes possessing a two-dimensional stacking fault structure are identified. For benzamide II polytypes, centric H-bonded amide dimers are found to be the preferred H-bonding motif. The stacking faults are also associated with conformational changes of phenyl rings, in agreement with observed diffraction intensities. A characteristic average structure containing the pertinent one-dimensional motifs is derived.

Methylphenylarsinic acid, MePhAsO·OH, a contaminant of rice plants and of groundwater, has been the subject of a single crystal X-ray study. In the crystal lattice the molecules form hydrogen-bonded chains linking O···HO entities; As–O, OH are 1.654(1), 1.719(1) Å.