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A novel approach to computationally enhance the sampling of molecular crystal structures is proposed and tested. This method is based on the use of extended variables coupled to a Monte Carlo based crystal polymorph generator. Inspired by the established technique of quasi‐random sampling of polymorphs using the rigid molecule constraint, this approach represents molecular clusters as extended variables within a thermal reservoir. Polymorph unit‐cell variables are generated using pseudo‐random sampling. Within this framework, a harmonic coupling between the extended variables and polymorph configurations is established. The extended variables remain fixed during the inner loop dedicated to polymorph sampling, enforcing a stepwise propagation of the extended variables to maintain system exploration. The final processing step results in a polymorph energy landscape, where the raw structures sampled to create the extended variable trajectory are re‐optimized without the thermal coupling term. The foundational principles of this approach are described and its effectiveness using both a Metropolis Monte Carlo type algorithm and modifications that incorporate replica exchange is demonstrated. A comparison is provided with pseudo‐random sampling of polymorphs for the molecule coumarin. The choice to test a design of this algorithm as relevant for enhanced sampling of crystal structures was due to the obvious relation between molecular structure variables and corresponding crystal polymorphs as representative of the inherent vapor to crystal transitions that exist in nature. Additionally, it is shown that the trajectories of extended variables can be harnessed to extract fluctuation properties that can lead to valuable insights. A novel thermodynamic variable is introduced: the free energy difference between ensembles of Z′ = 1 and Z′ = 2 crystal polymorphs. [ABSTRACT FROM AUTHOR]

Adducts of dimethylsulfoxide, dmso = Me2SO, with lanthanide(iii) picrates (picrate = 2,4,6-trinitrophenoxide, pic) of stoichiometry Ln(pic)3·3dmso have been prepared and characterised by single-crystal X-ray structure determinations as discrete, neutral, mononuclear molecular species. Such complexes have been obtained across the gamut of Ln, specifically for Ln = La, Pr, Nd, Sm, Gd, Dy, Yb, Lu, and Y, presumably also accessible for other intermediate members, the series being isomorphous (monoclinic, C 2/ c , Z = 8); a second triclinic P CH19169_IE1.gif form has also been identified for Ln = La, Pr. In both forms, the metal atom coordination environments are nine-coordinate, tricapped trigonal prismatic, [Ln(dmso- O)3(pic- O,O′)3], two of the three unidentate ligands lying in one of the trigonal planes and one in the other (an isomer we have termed meridional, mer). A hydrated form of Ln(pic)3·2dmso·H2O stoichiometry has also been defined for Ln = Sm, Gd, Lu, the metal atom environment again nine-coordinate, [Ln(dmso- O)2(H2 O)(pic- O,O′)3], but now fac , with the three unidentate ligands occupying one triangular face of the tricapped trigonal prism and involved in a centrosymmetric H-bonding array with the three similar ligands of an adjacent complex; the three capping atoms are nitro-oxygen atoms, the phenoxy- O triad occupying the other face. Structural characterisation of adducts of lanthanide picrates with dimethylsulfoxide has provided evidence that the 9-coordinate, tricapped trigonal-prismatic, mer -[Ln(pic)3(dmso)3] form with chelating picrate ligands may extend through the full series. Partial aquation of the tris(dmso) complexes to [Ln(pic)3(dmso)2(OH2)] provides three examples of an otherwise similar but facial isomer. [ABSTRACT FROM AUTHOR]

Single crystal X-ray structural characterisations are reported for adducts of the form [(L- O)Eu(O , O ′-dpm)3] obtained by the crystallisation of tris(dipivaloylmethanato)europium(iii) (dpm = [HC(C(tBu).CO)2]−) from an array of dipolar aprotic oxygen-donor solvents L (L = N -methylpyrrolidinone (nmp), trimethylphosphate, (MeO)3PO, (tmp), hexamethylphosphoramide (hmpa), dimethylacetamide (dma), dimethyl sulfoxide (dmso), and the bidentate octamethylpyrophosphoramide (ompa). In all adducts, the resulting arrays contain seven-coordinate metal atoms, which adopt two different isomeric forms of the mono-capped trigonal prismatic stereochemistry, the L = dma and dmso adducts corresponding to one type, nmp and tmp the other. The adduct formed with ompa behaves as a pair of discrete metal environments bridged by the O -ompa- O ′ ligand, thus; [(dpm- O , O ′)3Eu(O -ompa- O ′)Eu(O , O ′-dpm)3], and is found in two forms, one in which both Eu environments is of the tmp type, the other of the dmso/dma type. In the hmpa adduct, the asymmetric unit of the structure is a disordered composite of both types. In none of the adducts is there any further solvation beyond coordination of a single L. Structural studies of crystalline adducts of [Eu(dipivaloylmethanato)3] with dmso, dma, tmp, hmpa, and ompa have shown all to contain seven-coordinate EuIII. This low coordination number appears to be a consequence of partial coordination sphere interpenetration in the solid state. [ABSTRACT FROM AUTHOR]

Crystalline products of the reactions of lanthanide picrates, Ln(pic)3 (pic = 2,4,6-trinitrophenoxide), with hexamethylphosphoramide (hmpa) and octamethylpyrophosphoramide (ompa) have been characterised by single-crystal X-ray diffraction studies. With hmpa and lighter lanthanides (La, Sm, Eu), isomorphous species (monoclinic, P 21/ c , Z 4) of stoichiometry [Ln(pic)3(hmpa)3]·0.5H2O, have been defined where the molecular units in the lattice contain 9-coordinate Ln with tricapped trigonal-prismatic coordination geometry. The picrate ligands are bidentate through phenoxide-O and 2-nitro-O, with the latter occupying the capping positions, while the hmpa ligands are singly O-bound to one trigonal face. Heavier lanthanides (Gd, Lu) and Y have been found to give isomorphous (monoclinic, P 21/ n , Z 4) species of stoichiometry [Ln(pic)3(hmpa)2], with 8-coordinate Ln of an irregular geometry best considered as close to that of a bicapped trigonal-prism. The picrate ligands chelate in the same manner as in the lighter Ln complexes but with one spanning a trigonal edge, and the hmpa-O donors occuping two apices of the other trigonal face. The ligand ompa has been found to act as a bidentate chelate in all isolated species, displacing one picrate from the metal ion coordination sphere to give ionic complexes. For La, Nd, and Gd, isomorphous (monoclinic, P 21/ n , Z 4) complexes of stoichiometry [Ln(pic)2(ompa)2(OH2)](pic)·0.5H2O containing 9-coordinate, tricapped trigonal-prismatic Ln with a single aqua ligand have been defined, while for Er, Yb, Lu, and Y, both the coordinated and lattice water molecules are lost in isomorphous (monoclininc, P 21/ c , Z 8) 8-coordinate, square-antiprismatic species of stoichiometry [Ln(pic)2(ompa)2](pic). For Er, further polymorphs, one monoclinic, P 21/ c , and the other triclinic, CH19251_IE1.gif , have also been characterised. Structural studies of adducts of the lanthanide picrates with hexamethylphosphoramide (hmpa) and octamethylpyrophosphoramide (ompa) provide significant contrasts with those of analogous adducts with dimethylsulfoxide and trimethylphosphate. Adducts of hmpa show a transition from 9-coordinate (hmpa)3 to 8-coordinate (hmpa)2 species, while ompa displaces one picrate from the primary coordination sphere. [ABSTRACT FROM AUTHOR]

Adducts of the form Ln(pic)3(tmp)3 (Ln = lanthanide(iii); pic = picrate = 2,4,6-trinitrophenoxide; tmp = trimethylphosphate, (MeO)3PO) have been prepared for extremal Ln = La, Lu and some intermediate members, also Y, and characterised by single crystal X-ray structure determinations as unsolvated, mononuclear, molecular species. The lanthanide atom has nine-coordinate, tri-capped trigonal prismatic stereochemistry in all cases, the picrate components behaving as O , O ′-bidentate ligands chelating through the phenoxy- and an adjacent O -nitro oxygen atom, thus: [Ln(tmp- O)3(pic- O , O ′)3]. Two isomeric forms are found, one mer in which the three unidentate tmp- O ligands coordinate in cis -sites spanning the upper and lower triangles and a capping site of the coordination sphere, and fac , in which all three unidentate ligands occupy the mutually cis -sites of one triangular face. The mer isomer has been described as an isomorphous series in a monoclinic P 21/ c , Z 4, form, for Ln = La, Ce, Pr, Nd, Sm, Gd, Lu, and Y, presumptively accessible for the full gamut of Ln. The fac -isomer also crystallises in a monoclinic P 21/ c form, Z 8, two independent molecules of similar stereochemistry here comprising the asymmetric unit and described for Ln = Eu, Lu(isomorphous); it has also been described in a triclinic P CH19176_IE1.gif , Z 2 form for Ln = La. Trimethylphosphate (tmp) is the first of a series of related O-donor solvates of lanthanide(III) picrates to give isomeric mer- and fac- [Ln(pic)3(tmp)3] complexes. [ABSTRACT FROM AUTHOR]

Addition of various oxygen-donor ligands (L, all dipolar, aprotic solvents), to a solution of hydrated scandium picrate in weakly coordinating solvents (S), has yielded several crystalline adducts of the form Sc(pic)3(L) m (· n S) in which all ligands L are coordinated, subsequently characterised by a series of single crystal X-ray studies. For L = dmso, m = 3 and the picrate anions are all bound as phenoxide-O donor units, while for nmp, dma, tmp, and hmpa, m = 2 and one of the bound picrates becomes bidentate through phenoxide- and nitro-O donation. For L = ompa, m = 2 and two picrate ligands are bound through phenoxide-O while one is displaced from the primary coordination sphere. All complexes contain six-coordinate ScIII, confirming that this coordination number is a consequence of ligand bulk. Six-coordination of ScIII is observed throughout in crystalline adducts of scandium picrate with dmso, dma, nmp, tmp, hmpa, and ompa, although with variations in the adduct stoichiometry and the coordination mode of picrate. [ABSTRACT FROM AUTHOR]

The redox properties and the reactivity of several areneruthenium(II) 4-acyl-5-pyrazolonate derivatives are described.

In this paper, theories on anisotropic crystal growth and crystallization of atropisomers are reviewed and a model for anisotropic crystal growth from solution containing slow inter-converting conformers is presented. The model applies to systems with growth-dominated crystallization from solutions and assumes that only one conformation participates in the solute integration step and is present in the crystal lattice. Other conformers, defined as the wrong conformers, must convert to the right conformer before they can assemble to the crystal lattice. The model presents a simple implicit method for evaluating the growth inhibition effect by the wrong conformers. The crystal growth model applies to anisotropic growth in two main directions, namely a slow-growing face and a fast-growing face and requires the knowledge of solute crystal face integration coefficients in both directions. A parameter estimation algorithm was derived to extract those coefficients from data about temporal concentration and crystal size during crystallization and was designed to have a short run time, while providing a high-resolution estimation. The model predicts a size-dependent growth rate and simulations indicated that for a given seed size and solvent system and for an isothermal anti-solvent addition crystallization, the seed loading and the supersaturation at seeding are the main factors impacting the final aspect ratio. The model predicts a decrease of the growth inhibition effect by the wrong conformer with increasing temperature, likely due to faster equilibration between conformers and/or a decrease of the population of the wrong conformer, if of low energy, at elevated temperatures. Finally, the model predicts that solute surface integration becomes the rate-limiting mechanism for high solute integration activation energies, resulting in no impact of the WC on the overall crystal growth process. [ABSTRACT FROM AUTHOR]