Synthesis,Structure, and Properties of the High‐Pressure Modification of CePdSn – a 5 K Antiferromagnet

The high‐pressure (HP) modification of CePdSn was synthesized under multianvil high‐pressure (10.5 GPa) high‐temperature (1100 °C) conditions from the normal‐pressure (NP) modification. The structures of both modifications were studied by X‐ray powder and single crystal diffraction: TiNiSi type, Pnma, a = 754.1(2), b = 470.6(1), c = 798.4(3) pm, wR2 = 0.0333, 945 F² values, 20 variables for NP‐CePdSn and ZrNiAl type, , a = 760.03(5), c = 416.06(3) pm, wR2 = 0.0443, 248 F² values, 13 variables for HP‐CePdSn. The structural chemistry of both modifications is goverened by platinum centered trigonal prisms. The platinum and tin atoms in NP‐CePdSn and HP‐CePdSn build up a three‐dimensional [PdSn] network in which the cerium atoms fill channels. Susceptibility measurements on HP‐CePdSn reveal an experimental magnetic moment of 2.55(1) μ_B/Ce atom in the paramagnetic region. At 5 K a paramagnetic‐to‐antiferromagnetic transition is evident from magnetization and specific heat measurements.     

New Silver Tellurates – The Crystal Structures of a Third Modification of Ag2Te2O6 and of Ag4TeO5

Single crystals of a third modification of Ag₂Te₂O₆ (denoted as Ag₂Te₂O₆–III) and of Ag₄TeO₅ have been obtained as minor by‐products during hydrothermal phase formation experiments in the system Ag‐Hg‐Te‐O. The crystal structure of Ag₂Te₂O₆–III (P2₁/c, Z = 4, a = 6.4255(10), b = 6.9852(11), c = 13.204(2) Å, β = 90.090(3)°, 1885 independent reflections, R[F² > 2σ(F²)] = 0.0334, wR2(F² all) = 0.0817) comprises tellurium in oxidation states +IV and +VI and is topologically related to the structure of the Ag₂Te₂O₆–I modification, which consists of similar layers and interjacent layers of Ag⁺ cations. Ag₄TeO₅ (C2/c, Z = 8, a = 16.271(2), b = 6.0874(10), c = 11.4373(16) Å, β = 106.730(10)°, 2372 independent reflections, R[F² > 2σ(F²)] = 0.0288, wR2(F² all) = 0.0737) is made up of a layer‐like arrangement of isolated [Te^VI₂O₁₀] double octahedra and of Ag⁺ cations situated both in layers parallel and inside the layers of the anionic moieties.     

Synthetic Activators of Cell Migration Designed by Constructive Machine Learning

Constructive machine learning aims to create examples from its learned domain which are likely to exhibit similar properties. Here, a recurrent neural network was trained with the chemical structures of known cell-migration modulators. This machine learning model was used to generate new molecules that mimic the training compounds. Two top-scoring designs were synthesized, and tested for functional activity in a phenotypic spheroid cell migration assay. These computationally generated small molecules significantly increased the migration of medulloblastoma cells. The results further corroborate the applicability of constructive machine learning to the de novo design of druglike molecules with desired properties.     

New Rare‐Earth Metal Germanides RE2Ge9 (RE = Nd,Sm) by Thermal Decomposition of High‐Pressure Phases REGe5

The rare‐earth metal germanides RE₂Ge₉ (RE = Nd, Sm) have been prepared by thermal decomposition of the metastable high‐pressure phases REGe₅ at ambient pressure. The compounds adopt an orthorhombic unit cell with a = 396.34(4) pm; b = 954.05(8) pm and c = 1238.4(1) pm for Nd₂Ge₉ and a = 395.46(7) pm; b = 946.4(2) pm and c = 1232.1(3) pm for Sm₂Ge₉. Crystal structure refinements reveal space group Pmmn (No. 59) for Nd₂Ge₉. The atomic pattern resembles an ordered defect variety of the pentagermanide motif REGe₅ (RE = La; Nd, Sm, Gd, Tb) comprising corrugated germanium layers. These condense into a three‐dimensional network interconnected by eight‐coordinated germanium atoms. The resulting framework channels along [100] enclose the neodymium atoms. With respect to the atomic arrangement of the pentagermanides, half of the interlayer germanium atoms are eliminated in an ordered way so that occupied and empty germanium columns alternate along [001]. The rare‐earth metal atoms of both types of compounds, REGe₅ and RE₂Ge₉, exhibit the electronic states 4f ³ and 4f ⁵ (oxidation state +3) for neodymium and samarium, respectively, evidencing that the modification of the germanium network leaves the electron configuration of the metal atoms unaffected.     

Similarities and Differences between Crystal and Enzyme Environmental Effects on the Electron Density of Drug Molecules

The crystal interaction density is generally assumed to be a suitable measure of the polarization of a low-molecular weight ligand inside an enzyme, but this approximation has seldomly been tested and has never been quantified before. In this study, we compare the crystal interaction density and the interaction electrostatic potential for a model compound of loxistatin acid (E64c) with those inside cathepsin B, in solution, and in vacuum. We apply QM/MM calculations and experimental quantum crystallography to show that the crystal interaction density is indeed very similar to the enzyme interaction density. Less than 0.1 e are shifted between these two environments in total. However, this difference has non-negligible consequences for derived properties.     

Combined computational and experimental study of substituent effects on the thermodynamics of H(2), CO,arene, and alkane addition to iridium

The thermodynamics of small-molecule (H(2), arene, alkane, and CO) addition to pincer-ligated iridium complexes of several different configurations (three-coordinate d(8), four-coordinate d(8), and five-coordinate d(6)) have been investigated by computational and experimental means. The substituent para to the iridium (Y) has been varied in complexes containing the (Y-PCP)Ir unit (Y-PCP = eta(3)-1,3,5-C(6)H(2)[CH(2)PR(2)](2)Y; R = methyl for computations; R = tert-butyl for experiments); substituent effects have been studied for the addition of H(2), C-H, and CO to the complexes (Y-PCP)Ir, (Y-PCP)Ir(CO), and (Y-PCP)Ir(H)(2). Para substituents on arenes undergoing C-H bond addition to (PCP)Ir or to (PCP)Ir(CO) have also been varied computationally and experimentally. In general, increasing electron donation by the substituent Y in the 16-electron complexes, (Y-PCP)Ir(CO) or (Y-PCP)Ir(H)(2), disfavors addition of H-H or C-H bonds, in contradiction to the idea of such additions being oxidative. Addition of CO to the same 16-electron complexes is also disfavored by increased electron donation from Y. By contrast, addition of H-H and C-H bonds or CO to the three-coordinate parent species (Y-PCP)Ir is favored by increased electron donation. In general, the effects of varying Y are markedly similar for H(2), C-H, and CO addition. The trends can be fully rationalized in terms of simple molecular orbital interactions but not in terms of concepts related to oxidation, such as charge-transfer or electronegativity differences.     

Highly effective pincer-ligated iridium catalysts for alkane dehydrogenation. DFT calculations of relevant thermodynamic, kinetic, and spectroscopic properties

The p-methoxy-substituted pincer-ligated iridium complexes, (MeO-(tBu)PCP)IrH(4) ((R)PCP = kappa(3)-C(6)H(3)-2,6-(CH(2)PR(2))(2)) and (MeO-(iPr)PCP)IrH(4), are found to be highly effective catalysts for the dehydrogenation of alkanes (both with and without the use of sacrificial hydrogen acceptors). These complexes offer an interesting comparison with the recently reported bis-phosphinite "POCOP" ((R)POCOP = kappa(3)-C(6)H(3)-2,6-(OPR(2))(2)) pincer-ligated catalysts, which also show catalytic activity higher than unsubstituted PCP analogues (Gottker-Schnetmann, I.; White, P.; Brookhart, M. J. Am. Chem. Soc. 2004, 126, 1804). On the basis of nu(CO) values of the respective CO adducts, the MeO-PCP complexes appear to be more electron-rich than the parent PCP complexes, whereas the POCOP complexes appear to be more electron-poor. However, the MeO-PCP and POCOP ligands are calculated (DFT) to show effects in the same directions, relative to the parent PCP ligand, for the kinetics and thermodynamics of a broad range of reactions including the addition of C-H and H-H bonds and CO. In general, both ligands favor (relative to unsubstituted PCP) addition to the 14e (pincer)Ir fragments but disfavor addition to the 16e complexes (pincer)IrH(2) or (pincer)Ir(CO). These kinetic and thermodynamic effects are all largely attributable to the same electronic feature: O --> C(aryl) pi-donation, from the methoxy or phosphinito groups of the respective ligands. DFT calculations also indicate that the kinetics (but not the thermodynamics) of C-H addition to (pincer)Ir are favored by sigma-withdrawal from the phosphorus atoms. The high nu(CO) value of (POCOP)Ir(CO) is attributable to electrostatic effects, rather than decreased Ir-CO pi-donation or increased OC-Ir sigma-donation.