Dynamics of fracture in dissipative systems

Dynamics of fracture in two-dimensional systems is studied with a dissipative network model by including the local relaxation of the force field via Maxwellian viscoelasticity. In addition to disorder the fundamentals of crack formation and propagation depend on the strength of dissipation compared to the loading rate. We investigate the dynamics of a single crack and the role of stress reduction at the crack tip when dissipation is increased. As a consequence, the crack starts to propagate slowly and it reaches terminal velocity later. If the relaxation of local forces is strong enough compared with crack velocity, crack arrest takes place. For a disordered system, the presence of strong dissipation in local dynamics is reflected as ductility and as an increase in the damage, accumulated during the fracture process.Peer reviewe

Dissipative dynamic fracture of disordered systems

Breakdown of two-dimensional disordered systems is studied with a time-dependent network model. The dependence of fracture process on the local relaxation of the force field is included within the framework of Maxwellian viscoelasticity. The dynamics and characteristics of crack formation and propagation are shown to depend on disorder and relative time scales of dissipation and loading. Brittle behavior is encountered in the adiabatic limit of slow straining. At finite strain rates, the development of damage shows ductile behavior with increasing dissipation. Nucleation of cracks in various dynamical situations is discussed.Peer reviewe

Halogen Bonding between Thiocarbonyl Compounds and 1,2- and 1,4-Diiodotetrafluorobenzenes

The halogen bonding (XB) between 1,2-diiodotetrafluorobenzene (1,2-DITFB) or 1,4-diiodotetrafluorobenzene (1,4-DITFB) and the selection of different thiocarbonyl acceptors was studied by the single-crystal X-ray diffraction method. Diiodotetrafluorobenzenes (DITFBs) were found to form C-I···S halogen-bonded 1:1, 2:1, and 1:2 (donor/acceptor ratio) complexes with thiocarbonyls. Lengths of contacts were found to be clearly shorter than the sum of van der Waals radii of iodine and sulfur as well as the contact angles showed values close to linear, so the XB interactions could be verified. One sulfur atom showed the ability to accept one, two, or four XB interactions, and the acceptor angle can vary more than 35°. Solid-state packing of thiocarbonyl-XB complexes was found to be greatly affected by the size and type of the acceptor used. Halogen and hydrogen bonding cooperativity was found in some of the complexes if the used acceptor was suitable to form both bonds. Here, we present 19 new structures of these complexes, which can be rather easily prepared by mixing the components in the solutions and letting them crystallize in loosely sealed tubes. Computational analysis carried out for the XB complexes of N,N′-dimethylthiourea supported very closely the findings of the experimental study.peerReviewe

Low‐valent Germanylidene Anions : Efficient Single‐site Nucleophiles for Activation of Small Molecules

Rare mononuclear and helical chain low-valent germanylidene anions supported by cyclic (alkyl)(amino) carbene and hypermetallyl ligands were synthesized by stepwise reduction from corresponding germylene precursors via stable acyclic germanium radicals. The germanylidene anions can be described with ylidene and ylidone resonance forms of which the latter becomes prevalent when engaging with electrophiles. Reactions of CO 2 resulted in the formation of μ-CO 2 -κC:κO adducts, a previously uncharacterized coordination mode for low-valent germanium and inaccessible for related neutral ylidones. These results implicate low-valent germanylidene anions as efficient single-site nucleophiles for activation of small molecules.peerReviewe

The C–I･･･⁻O–N⁺ Halogen Bonds with Tetraiodoethylene and Aromatic N-oxides

The nature of C–I⋯⁻O–N⁺ interactions, first of its kind, between non-fluorinated tetraiodoethylene XB-donor and pyridine N-oxides (PyNO) are studied by single-crystal X-ray diffraction (SCXRD) and Density Functional Theory (DFT) calculations. Despite the non-fluorinated nature of the C2I4, the I⋯O halogen bond distances are similar to well-known perfluorohaloalkane/-arene donor-PyNO analogues. With C2I4, oxygens of the N-oxides adopt exclusively 2-XB-coordination in contrast to the versatile bonding modes observed with perfluorinated XB-donors. The C2I4 as the XB donor forms with PyNO’s one-dimensional chain polymer structures in which the C2I4⋯(μ-PyNO)2⋯C2I4 segments manifesting two bonding motifs, namely, side-by-side (vicinal di-iodo) and head-to-head (geminal di-iodo), due to the nearly symmetric square planar structure of the C2I4. While the attractive nature between I- and O-atoms is mainly electrostatic, the narrow range of C⋯O bond parameters demonstrate that the -bond between four iodine atoms also plays an important role in enhancing the -hole strength. DFT-based monodentate XB interaction energies, ΔEint, in thirteen 1:1 XB complexes vary between 31.9 – 46.5 kJ mol–1, the strongest remarkably exceeding the value reported for I–I⋯⁻O–N⁺ = 42.0 kJ mol–1. In case of C2I4･(pyridine N-oxide) [31.9 kJ mol–1], the monodentate XB energy is on a par with perfluorinated donor complexes, namely, CF3I･(pyridine N-oxide) [31.1 kJ mol–1] and C6F5I･(pyridine N-oxide) [32.3 kJ mol–1].peerReviewe

Ruthenium‐assisted tellurium abstraction in bis(thiophen‐2‐yl) ditelluride

The reaction of [RuCl2(CO)3]2 and Te2Tpn2 (Tpn = thiophen-2-yl, C4H3S) in the absence of light resulted in the formation of cct-[RuCl2(CO)2(TeTpn2)2] (1) [cis(Cl)-cis(CO)-trans(TeTpn2)] and TeTpn2 (2) together with the precipitation of tellurium. The complex 1 and the monotelluride 2 were characterized by NMR spectroscopy and single-crystal X-ray diffraction. The decomposition of Te2Tpn2 to TeTpn2 has been monitored by 125Te NMR spectroscopy and seemed to be faster than the ligand substitution in [RuCl2(CO)3]2 by TeTpn2. A catalytic cycle is proposed for the decomposition of Te2Tpn2 to TeTpn2 based on the PBE0-D3/def2-TZVP calculations.peerReviewe

Titanocene selenide sulfides revisited:formation, stabilities, and NMR spectroscopic properties

Abstract [TiCp2S5] (phase A), [TiCp2Se5] (phase F), and five solid solutions of mixed titanocene selenide sulfides [TiCp2SexS5−x] (Cp = C5H5−) with the initial Se:S ranging from 1:4 to 4:1 (phases B–E) were prepared by reduction of elemental sulfur or selenium or their mixtures by lithium triethylhydridoborate in thf followed by the treatment with titanocene dichloride [TiCp2Cl2]. Their 77Se and 13C NMR spectra were recorded from the CS2 solution. The definite assignment of the 77Se NMR spectra was based on the PBE0/def2-TZVPP calculations of the 77Se chemical shifts and is supported by 13C NMR spectra of the samples. The following complexes in varying ratios were identified in the CS2 solutions of the phases B–E: [TiCp2Se5] (51), [TiCp2Se4S] (41), [TiCp2Se3S2] (31), [TiCp2SSe3S] (36), [TiCp2SSe2S2] (25), [TiCp2SSeS3] (12), and [TiCp2S5] (01). The disorder scheme in the chalcogen atom positions of the phases B–E observed upon crystal structure determinations is consistent with the spectral assignment. The enthalpies of formation calculated for all twenty [TiCp2SexS5−x] (x = 0–5) at DLPNO-CCSD(T)/CBS level including corrections for core-valence correlation and scalar relativistic, as well as spin-orbit coupling contributions indicated that within a given chemical composition, the isomers of most favourable enthalpy of formation were those, which were observed by 77Se and 13C NMR spectroscopy

Computational thermochemistry : extension of Benson group additivity approach to organoboron compounds and reliable predictions of their thermochemical properties

High-level computational data for standard gas phase enthalpies of formation, entropies, and heat capacities are reported for 116 compounds of boron. A comparison of the results with extant experimental and computational benchmark values reveals important trends and clear outliers. Recommendations are made to revise some of the key quantities, such as the enthalpies of formation of orthoboric acid, trimethylthioborate, and triphenylborane, the last of which is found to be considerably in error. The uncertainties associated with the experimental values are found to exceed those of high-level calculations by a clear margin, prompting the redetermination of Benson group additivity contributions for boron-based groups on purely computational grounds. The applicability of the established group contribution values is demonstrated by estimating thermochemical data for large organoboron compounds that cannot be treated with high-level quantum chemical methods and comparing the results with existing experimental and computational values.peerReviewe

High-Level Ab Initio Predictions of Thermochemical Properties of Organosilicon Species : Critical Evaluation of Experimental Data and a Reliable Benchmark Database for Extending Group Additivity Approaches

A high-level composite quantum chemical method, W1X-1, is used herein to calculate the gas-phase standard enthalpy of formation, entropy, and heat capacity of 159 organosilicon compounds. The results set a new benchmark in the field that allows, for the first time, an in-depth assessment of existing experimental data on standard enthalpies of formation, enabling the identification of important trends and possible outliers. The calculated thermochemical data are used to determine Benson group additivity contributions for 60 Benson groups and group pairs involving silicon. These values allow fast and accurate estimation of thermochemical parameters of organosilicon compounds of varying complexity, and the data acquired are used to assess the reliability of experimental work of Voronkov et al. that has been repeatedly criticized by Becerra and Walsh. Recent results from other computational investigations in the field are also carefully discussed through the prism of reported advancements.peerReviewe

Halogen-Bonded Mono-, Di-, and Tritopic N-Alkyl-3-iodopyridinium Salts

Halogen bonding interactions of 15 crystalline 3-iodopyridinium systems were investigated. These systems were derived from four N-alkylated 3-iodopyridinium salts prepared in this study. The experimental results in the solid state show that halogen bonding acts as a secondary intermolecular force in these charged systems but sustains the high directionality of interaction in the presence of other intermolecular forces. Halogen bonds donated by polytopic 3-iodopyridinium cations are also sufficient to enclose guest molecules inside the formed supramolecular cavities. The experimental data were supplemented by computational gas-phase and solid-state studies for selected halogen-bonded systems. Calculations of the model systems with the increasing number of halogen bond donors and acceptors showed the halogen bond strengths to be exaggerated for the smallest of model systems. The agreement between experimental and calculated structures improved for larger systems that were able to account for the influence of other intermolecular interactions. The best agreement between experimental and calculated structural parameters were found for solid-state calculations with periodic boundary conditions. Comparison of the halogen bond interaction strengths with the strength of other lattice interactions showed the halogen bonds to come second to electrostatic interactions in stabilizing the structures but having a major role in directing the packing of the solid-state structures.peerReviewe