A conformational polymorph of Ph3PAu[SC(OEt)=NPh] featuring an intramolecular Au···π interaction

Abstract A conformational polymorph, form β, for Ph3PAu[SC(OEt)=NPh] has been characterised. Like the original structure (form α), the molecule features a linear P–Au–S geometry. The difference between molecular structures rests with the relative disposition of the thiolate ligand which places the N-bound aryl ring in close proximity to the gold centre (form β) rather than the oxygen atom (form α). Density functional theory calculations show the molecule with the Au···π interaction is more stable by 5.2 kcal/mol than the one with the Au···O contact. The molecular packing of both forms are stabilised by C–H···O and C–H···π interactions which make approximately the same contribution to the overall Hirshfeld surfaces. However, key indicators, e.g. crystal packing efficiency and density, and the computational results suggest form β is the thermodynamically favoured form.</jats:p

Snap frozen! Capturing two metastable polymorphs in a tetramorphic one-dimensional coordination polymer constructed from cadmium, dithiophosphate, and 4-pyridinealdazine

Four polymorphs are described for the one-dimensional coordination polymer {Cd[S2P(OMe)2]2(4-pyridine-aldazine)}n (1) which features a trans-N2S4 distorted octahedral coordination geometry. Lattice energy calculations show the room temperature form, 1α, is the thermodynamically stable phase, being 1.52 kcal/mol more stable than the 1β form per unit formula. The latter is formed at 233 K on cooling 1α based on single crystal data. Single crystals of forms 1α and 1β exhibit a reversible single-crystal-single-crystal phase change which also 2 occurs in the bulk form as seen in DSC and PXRD experiments. When 1 was “snap frozen” at 100 K under a cold stream, 1β was observed most of the time but sometimes forms 1γ and 1δ were found. When warmed, 1β converted to 1α by 293 K, and each of 1γ and 1δ first converted to 1β (120-130 and 140-150 K, respectively) and then to 1α (280 K), correlating with the calculated lattice energies; subsequent cooling only yielded 1β, indicating 1γ and 1δ are metastable forms. The polymorphs exhibit different molecular packing patterns based on different non-covalent interactions and these have been evaluated by Hirshfeld surface analyses and NCI plots

Compressibility and phase stability of iron-rich ankerite

ABSTRACT: The structure of the naturally occurring, iron-rich mineral Ca₁․₀₈(₆)Mg₀.₂₄(₂)Fe₀.₆₄(₄)Mn₀.₆₄(₄)(CO₃)₂ ankerite was studied in a joint experimental and computational study. Synchrotron X-ray powder diffraction measurements up to 20 GPa were complemented by density functional theory calculations. The rhombohedral ankerite structure is stable under compression up to 12 GPa. A third-order Birch-Murnaghan equation of state yields V₀ = 328.2(3) ų, bulk modulus B₀ = 89(4) GPa, and its first-pressure derivative B'₀ = 5.3(8)-values which are in good agreement with those obtained in our calculations for an ideal CaFe(CO₃)₂ ankerite composition. At 12 GPa, the iron-rich ankerite structure undergoes a reversible phase transition that could be a consequence of increasingly non-hydrostatic conditions above 10 GPa. The high-pressure phase could not be characterized. DFT calculations were used to explore the relative stability of several potential high-pressure phases (dolomite-II-, dolomite-III- and dolomite-V-type structures), and suggest that the dolomite-V phase is the thermodynamically stable phase above 5 GPa. A novel high-pressure polymorph more stable than the dolomite-III-type phase for ideal CaFe(CO₃)₂ ankerite was also proposed. This high-pressure phase consists of Fe and Ca atoms in sevenfold and ninefold coordination, respectively, while carbonate groups remain in a trigonal planar configuration. This phase could be a candidate structure for dense carbonates in other compositional systems.This research was funded by the Spanish Ministerio de Ciencia, Innovación, y Universidades (MICINN) under the projects MALTA Consolider Ingenio 2010 network MAT2015-71070-REDC and PGC2018-097520-A-I00 (co-financed by EU FEDER funds), and by the Generalitat Valenciana under project PROMETEO/2018/123. D.S.-P. and A.O.R. acknowledge the financial support of the Spanish MINECO for the RyC-2014-15643 and RyC-2016-20301 Ramon y Cajal Grants, respectively. C.P acknowledges the financial support of the Spanish Ministerio de Economia y Competitividad (MINECO project FIS2017-83295-P)

Exploring C-H∙∙∙metalloaromatic interactions

The C-H···metalloaromatic interaction is an of intermolecular contact which is less explored compared to the common secondary interactions such as hydrogen bonding and π··· π stacking. A series of 12 palladium(II) xanthate complexes was prepared by varying the xanthate side group from one carbon to six carbons, i.e. primary, secondary and tertiary hydrocarbons. All 12 complexes were crystallised and the intermolecular interactions present in each system were delineated. Among the series, 11 out of 12 palladium(II) xanthates showed at least one pair of the anticipated C-H···metalloaromatic π interaction, and up to a maximum of six pairs as identified in Pd[S2CO(neo-hexyl)]2. Further, the CH···metalloaromatic π interactions led to the formation of zero, one and even two dimensional motifs in the respective crystals. From a computational chemistry study performed on Pd[S2CO(n-propyl)]2, it is revealed that a C-H···metalloaromatic π interaction is of similar strength as intermolecular Pd···S secondary bonding which led to the dimerisation of palladium(II) xanthate in the condensed phase

Hydrogen bonding in 2,6-bis(4-fluorophenyl)-3,5-dimethylpiperidin-4-one methanol solvate

The crystal structure analysis of a 2,6-diaryl 4-piperidone derivative, isolated as a mono-methanol solvate, reveals that both the piperidone and the methanol molecule lie on a crystallographic mirror plane. A chair conformation is found for the piperidone ring with the aryl and methyl groups in equatorial positions. The most prominent feature of the molecular packing is the formation of supramolecular zigzag chains mediated by amine-N–H···O(methanol) and hydroxyl-O–H···N(amine) hydrogen bonds, i.e. the methanol molecule serves as a bridge between piperidone molecules. The molecular structure is compared with that determined in an unsolvated form and the gas-phase equilibrium structure, obtained using density-functional theory (DFT); differences relate, in the main, to the relative dispositions of the aryl rings. An analysis of the Hirshfeld surfaces of the experimental structures indicates very similar relative contributions with the notable exception being the contribution by O···H/H···O which at 13.7% in the methanol solvate is >8.5% in the unsolvated form

Experimental and computational evidence for a stabilising C–Cl(lone-pair)⋯π(chelate-ring) interaction

In addition to a variety of conventional non-covalent intermolecular interactions such as C–H…π(arene), C–H…Cl and π(arene)…π(chelate-ring) contacts, the molecular packing in the crystal of an organotin dithiocarbamate compound, [SnCl(4-ClC6H4)2{S2CN(i-Pr)2}], exhibits evidence for a C–Cl…π(chelate-ring) interaction. These interactions occur via a side-on approach of the chloride atom to the chelate-ring and therefore, are characterised as C–Cl(lone pair)…π(chelate-ring) interactions, are shown to be attractive by NCI plots and QTAIM analysis, and are apparent in the calculated Hirshfeld surfaces. Theory suggests the energy of association provided the C–Cl…π(chelate-ring) interactions to be about 3-4 kcal/mol, a value greater than for analogous C–Cl…π(arene) and C–H…π(arene) interactions. A survey of the literature of related structures suggests these interactions are not common. The newly described C–Cl(lone-pair)…π(chelate-ring) interactions add to the variety of intermolecular interactions able to be formed by chelate-rings in the supramolecular chemistry of metal complexes

Crystallographic and computational study of t-butyl N-[3-hydroxy-1-phenyl-4-(pyridin- 2-ylsulfanyl)butan-2-yl]carbamate and its pyrimidin-2-yl analogue

Abstract The crystal structure analysis of the biologically-relevant title compound (1) shows the carbonyl-O2 and amide-H atoms to be anti, and perpendicular relationships between the carbamate residue and the pyridyl ring [dihedral angle=84.60(10)°] and between the carbamate and aryl ring [74.84(11)°]; the rings are approximately co-planar [12.07(17)°]. An intramolecular hydroxyl-O–H···N(pyridyl) hydrogen bond that closes a S(7) loop is noted. Of interest is the observation that this hydrogen bond is not found in the structure of the pyrimidinyl analogue (2) which was characterised as a monohydrate, i.e. 2·H2O, in an earlier study. Density-functional theory calculations show the observed conformation in 1 is 2.0 kcal/mol more stable than the conformation where the intramolecular hydrogen bond is absent. This energy difference reduces to ca 0.5 kcal/mol in the case of 2. The differences in molecular conformations found for 1 and 2 are therefore ascribed to the dictates of overall molecular packing, in particular due to the influence of lattice water in 2·H2O.</jats:p

Transition path to a dense efficient-packed post-delafossite phase. Crystal structure and evolution of the chemical bonding

[EN] A(I)B(III)O(2) delafossite-type oxides are important technological compounds characterized by the linear coordination of the monovalent A metal by oxygen atoms. Based on results of in situ synchrotron X-ray diffraction measurements and ab initio calculations, we herein report on the high-pressure behavior of AgGaO2, to the best of our knowledge the first compound showing step-wise transitions of Ag coordination from linear (2) to octahedral (6), through a leaning delafossite structure. These transformations take place at similar to 10.5 and similar to 16.5 GPa, respectively. Our structural analysis evidences that the initial rhombohedral delafossite structure first becomes dynamically unstable, and distorts continuously via a gliding motion of the [GaO2] octahedral layers within the ab plane, and subsequently transform into another rhombohedral phase 8% denser. This structural sequence is associated with a simultaneous decrease in the bond order of the Ag-O bonds and an increase in the ionicity of the crystal. These results may help to unveil the high-pressure phases of several delafossite compounds which were reported to undergo phase transitions under compression that could not be identified.We are thankful for the financial support received from the Spanish Ministerio de Ciencia e Innovacion and the Agencia Estatal de Investigacion under national projects PGC2018-094417-B-I00 (co-financed by EU FEDER funds), MAT2016-75586-C4-1-P/2-P, FIS2017-83295-P, PID2019-106383GB-C41/C42 and RED2018-102612-T (MALTA Consolider), and from Generalitat Valenciana under project PROMETEO/2018/123. D.S-P, A.O.R, and J.A.S acknowledge financial support of the Spanish MINECO for the RyC-2014-15643, RyC-2016-20301, and RyC-2015-17482 Ramon y Cajal Grants, respectively. Authors thank ALBA-CELLS synchrotron for providing beamtime (ALBA experiments 2012010170).Chuliá-Jordán, R.; Santamaria-Perez, D.; Pellicer-Porres, J.; Otero-De-La-Roza, A.; Martinez-Garcia, D.; García-Domene, B.; Gomis, O.... (2021). Transition path to a dense efficient-packed post-delafossite phase. Crystal structure and evolution of the chemical bonding. Journal of Alloys and Compounds. 867. https://doi.org/10.1016/j.jallcom.2021.15901215901286

Pressure-induced spin transition and site-selective metallization in CoCl2

The interplay between spin states and metallization in compressed CoCl 2 is investigated by combining diffraction, resistivity and spectroscopy techniques under high-pressure conditions and ab-initio calculations. A pressure-induced metallization along with a Co 2+ high-spin (S = 3/2) to low-spin (S = 1/2) crossover transition is observed at high pressure near 70 GPa. This metallization process, which is associated with the p-d charge-transfer band gap closure, maintains the localization of 3d electrons around Co 2+ , demonstrating that metallization and localized Co 2+ -3d low-spin magnetism can coexist prior to the full 3d-electron delocalization (Mott-Hubbard d-d breakdown) at pressures greater than 180 GPa.Financial support from the Spanish Ministerio de Economıa y Competitividad (Project No. MAT2015-69508-P, MAT2016-80438-P) and MALTA-CONSOLIDER (Ref. No. MAT2015-71070-REDC) is acknowledged