Temperature-dependent Crystal Structures Research Articles

Large Phase-Transition Temperature Enhancement Achieved in a Layered Lead Iodide Hybrid Crystal by H/F Substitution.

Organic-inorganic hybrid metal halides with structural flexibility and solution processability have been widely investigated for different application scenarios. However, the effective construction of phase-transition materials with a high phase-transition temperature (Ttr) for potential practical applications remains a great challenge, and reports on the regulation of Ttr with significant enhancement have been rare. In this manuscript, we have realized a large Ttr increase of 148 K in a layered hybrid lead iodide crystal (4-FTMBA)4Pb3I10 (4-FTMBA = 4-fluoro-N,N,N-trimethylbenzenaminium) by the H/F substitution strategy. Compared to the parent (TMBA)4Pb3I10 (TMBA = N,N,N-trimethylbenzenaminium), H/F substitution preserves the structural framework and crystal symmetry in (4-FTMBA)4Pb3I10. The introduction of heavier fluorine will significantly increase the motion barrier for the order-disorder transition, resulting in the remarkably improved Ttr. Temperature-dependent crystal structures, Raman spectra, and dielectric analyses well support the phase-transition behavior. In addition, evident thermochromism with a tunable direct band gap in (4-FTMBA)4Pb3I10 has been observed using UV-vis spectra. To the best of our knowledge, the achieved Ttr enhancement of 148 K by H/F substitution is the highest among the organic-inorganic hybrid lead halide phase-transition materials. This finding would greatly inspire the rational design of functional materials with high performance.

Molecular motions of a tetraphenylethylene-derived AIEgen directly monitored through in situ variable temperature single crystal X-ray diffraction

The isotropic displacement parameters of each phenyl ring confirm the inequivalent vibrations of a crystalline tetraphenylethylene-derived AIEgen.

Incorporating dual BCC/FCC Zerilli-Armstrong and blue brittleness constitutive material models into Oxley’s machining shear zone theory

This work presents an extension of Oxley's shear zone theory by substituting the original velocity-modified power form by the widely used constitutive material model developed by Zerilli and Armstrong (ZA). Used are variations of ZA constitutive laws capable of accounting for operating strains, strain rates, and temperatures as well as the appropriate crystal structure such as body-centered cubic (BCC) and face-centered cubic (FCC). This latter feature is useful in cutting simulations of metal alloys with complex phase diagrams (e.g., carbon steels) having temperature-dependent crystal structures. Loss of ductility encountered at elevated temperatures, dubbed Blue Brittleness (BB), adds another challenge to the simulations.For validation purposes, cutting and thrust forces of single-phase Aluminum 6061-T6 (FCC crystal structure) were investigated. Additionally, and in order to illustrate the utility of the methodology for dual phase materials, AISI 1045 steel was utilized as a metal with temperature-dependent crystal structure that evolve from BCC to FCC as temperatures increase due to increasingly aggressive cutting parameters. The simulations utilized publicly available cutting force values from orthogonal machining tests conducted at different cutting speeds and feeds. For both 6061-T6 Aluminum and AISI 1045 steel, the methodology of extending Oxley’s thick shear zone analysis by incorporating the widely used Zerilli-Armstrong constitutive laws (dual BCC/FCC) was shown to produce accurate estimates of forces and chip thickness over a wide range of cutting conditions.

Correction: Anion- and temperature-dependent assembly, crystal structures and luminescence properties of six new Cd(ii) coordination polymers based on 2,3,5,6-tetrakis(2-pyridyl)pyrazine

Correction for ‘Anion- and temperature-dependent assembly, crystal structures and luminescence properties of six new Cd(II) coordination polymers based on 2,3,5,6-tetrakis(2-pyridyl)pyrazine’ by Jun Wang et al., CrystEngComm, 2016, 18, 5164–5176.

Anion- and temperature-dependent assembly, crystal structures and luminescence properties of six new Cd(ii) coordination polymers based on 2,3,5,6-tetrakis(2-pyridyl)pyrazine

Solvothermal reactions of 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) and sodium azide with different cadmium salts including CdCl2·2.5H2O, Cd(NO3)2 and Cd(CH3COO)2·2H2O at 80 °C produce three new coordination polymers, namely, {[Cd2(N3)2(tppz)Cl2]·2H2O}n (1), [Cd2(N3)2(tppz)(NO3)2]n (2) and {[Cd2(N3)2(tppz)(CH3COO)2]·2H2O}n (3), respectively. Single-crystal X-ray diffraction analysis reveals that the anions of the Cd(II) salts all participate in coordination in compounds 1–3. Compound 1 features an infinite one-dimensional (1D) chain with loops-and-rods topology, compound 2 exhibits a 1D ladder-like chain, while compound 3 possesses a 2D honeycomb-like network structure with (6,3) topology. The low-dimensional structures of compounds 1–3 are further stabilized by diverse supramolecular interactions such as hydrogen bonds and π⋯π stacking. Interestingly, when the temperature is increased to 100 °C, similar reactions of tppz and sodium azide ligands with CdCl2·2.5H2O, Cd(NO3)2 and Cd(CH3COO)2·2H2O lead to three other novel 3D Cd(II) coordination polymers formulated as [Cd3(N3)6(tppz)]n (4), {[Cd2(N3)2(tppz)(NO3)2]·MeOH}n (5) and [Cd4(N3)6(tppz)(CH3COO)2]n (6), respectively. The anions of the Cd(II) salts again take part in coordination in compounds 5 and 6 but disappear in the final structure of 4. Compound 4 displays a rare sxd-type 3D framework with the Schlafli symbol of (33·46·55·6) if each V-shaped trinuclear [Cd3(μ1,1-N3)4] secondary building unit (SBU) is regarded as a 6-connected node. In compound 5, both the Cd1 and Cd2 atoms serve as 3-connected nodes to construct an uncommon binodal (3,3)-connected 3D framework with (6·102)(62·10) topology. Compound 6 contains another type of V-shaped trinuclear [Cd3(μ1,1-N3)2(μ3-CH3COO)] SBU, which acts as a 7-connected node to fabricate a unique uninodal 7-connected 3D framework with a completely new topology of (36·42·510·63). The present results reveal that both anions and temperature play essential roles in the structural and topological diversity of such six new Cd(II) coordination polymers. Moreover, the IR spectra, thermogravimetric analysis curves, and solid-state luminescence properties of all the compounds have been also investigated. Compared with the free tppz ligand, compounds 1–6 exhibit superior luminescence properties with largely enhanced emission, indicating that they may be good candidates for optical materials.

A High‐Temperature Neutron Diffraction and First‐Principles Study of Ti3AlC2 and Ti3(Al0.8Sn0.2)C2

Herein, we report on the temperature‐dependent crystal structures of Ti 3 AlC 2 and Ti 3 Al 0.8 Sn 0.2 C 2 in the 373–1273 K temperature range, as determined by Rietveld analysis of high‐temperature neutron diffraction time‐of‐flight data. The compositions are 86(1) wt% Ti 3 AlC 2 and 14(1) wt% TiC 0.92(2) for the sample with no Sn , and 95(1) wt% Ti 3( Al 0.8 Sn 0.2) C 2 and 5(1) wt% Ti 2 AlC for the solid solution with Sn . The average linear volumetric thermal expansion is 8.0(2) × 10−6 K −1 for Ti 3 AlC 2 and 8.2(5) × 10−6 K−1 for Ti 3( Al 0.8 Sn 0.2) C 2. The average linear thermal expansion in the a and c directions, respectively, are 7.6(2) × 10−6 K−1 and 8.9(2) × 10−6 K−1 for Ti 3 AlC 2. For Ti 3( Al 0.8 Sn 0.2) C 2, the respective values are 8.0(5) × 10−6 K−1 and 8.6(6) × 10−6 K−1. In the case of the solid solution, the quadratic thermal expansion coefficients are also given. Detailed bond lengths analysis shows that the thermal expansions along the a and c directions are controlled by the thermal expansions of the Ti – C , and Ti – Al bond lengths, respectively. The atomic displacement parameters (ADPs) show that the Al and Sn atoms vibrate with a higher amplitude than the Ti and C atoms. Consistent with first‐principles calculations, the ADPs of the Al/Sn site(s) in Ti 3( Al 0.8 Sn 0.2) C2 are lower than the ADPs of Al in Ti 3 AlC 2.

High-temperature neutron diffraction and first-principles study of temperature-dependent crystal structures and atomic vibrations in Ti3AlC2, Ti2AlC, and Ti5Al2C3

Herein we report on the thermal expansions and temperature-dependent crystal structures of select ternary carbide Mn+1AXn (MAX) phases in the Ti–Al–C phase diagram in the 100−1000 °C temperature range. A bulk sample containing 38(±1) wt. % Ti5Al2C3 (“523”), 32(±1) wt. % Ti2AlC (“211”), 18(±1) wt. % Ti3AlC2 (“312”), and 12(±1) wt. % (Ti0.5Al0.5)Al is studied by Rietveld analysis of high-temperature neutron diffraction data. We also report on the same for a single-phase sample of Ti3AlC2 for comparison. The thermal expansions of all the MAX phases studied are higher in the c direction than in the a direction. The bulk expansion coefficients—9.3(±0.1)×10−6 K−1 for Ti5Al2C3, 9.2(±0.1) ×10−6 K−1 for Ti2AlC, and 9.0(±0.1)×10−6 K−1 for Ti3AlC2—are comparable within one standard deviation of each other. In Ti5Al2C3, the dimensions of the Ti–C octahedra for the 211-like and 312-like regions are comparable to the Ti–C octahedra in Ti2AlC and Ti3AlC2, respectively. The isotropic mean-squared atomic displacement parameters are highest for the Al atoms in all three phases, and the values predicted from first-principles phonon calculations agree well with those measured.

Polynuclear copper(ii) pyrazolate complexes: temperature-dependent protonolysis reactions, crystal structures and high catalytic activity toward the condensation of nitriles with 2-aminoalcohol

Reaction of Cu(OAc)2·H2O and 1H-pyrazole-3,5-dicarboxylic acid dimethyl ester (Hdcmpz) in MeOH at room temperature afforded one tetranuclear Cu(II)/pyrazolate complex [{Cu2(μ-OAc)2}2(μ-dcmpz)2(μ-OAc)2] (1) in 89% yield. The similar reaction in refluxing MeOH produced a hexanuclear metallamacrocyclic Cu(II)/pyrazolate complex [{Cu(μ-dcmpz)}2(μ-OMe)2]3 (2) in 85% yield. Treatment of the same components under solvothermal conditions resulted in the formation of another tetranuclear Cu(II)/pyrazolate/carboxylate complex [{Cu(MeOH)}4(μ-mcccpz)4] (3, Hmcccpz = 5(3)-(methoxycarbonyl)-1H-pyrazole-3(5)-carboxylic acid) in 30% yield. The mcccpz(2-) ion in 3 was in situ generated via the hydrolysis of one of two esters on dcmpz ligand. Complexes 1-3 were characterized by elemental analysis, IR and single-crystal X-ray diffraction. An X-ray analysis revealed that 1 contains two {Cu(μ-OAc)}2 fragments that are interconnected by two μ-η(2),η(2)-dcmpz(-) ligands and two μ-η(1),η(1)-OAc(-) ions, forming a unique tetrameric structure. Complex 2 is composed of three {Cu(μ-dcmpz)}2 fragments linked by three pairs of μ-OMe(-) anions, forming a metallamacrocyclic crown structure. 3 consists of four {Cu(MeOH)} fragments linked by two pairs of μ-η(1),η(2)-mcccpz(2-) ligands, forming a tetrameric [2 × 2] grid-like structure. Complexes 1-3 displayed high catalytic activity toward the condensation of nitriles with 2-aminoalcohol under solvent-free conditions to produce various 2-oxazolines.

Temperature-Dependent Crystal Structures of Ti2AlN and Cr2GeC as Determined from High Temperature Neutron Diffraction

In this work, we report on the temperature-dependent crystal structures of the isostructural, layered hexagonal phases Ti2AlN and Cr2GeC determined by Rietveld analysis of high temperature neutron powder diffraction data of fully dense, polycrystalline, bulk samples in the 100° to 1100°C temperature range. For both phases, the A-group atoms, Al and Ge, vibrate with the highest amplitude and do so anisotropically within the basal plane. All bonds expand linearly with temperature, with the highest relative thermal expansion occurring in the Ti–Al and Cr–Ge bonds. The thermal expansion coefficients in the a- and c-direction are, respectively, 10.3(±0.2) × 10−6 and 9.3(±0.2) × 10−6 K−1 for Ti2AlN and 12.8(±0.3) × 10−6 and 14.6(±0.3) × 10−6 K−1 for Cr2GeC. The unit cell volume expansions observed by HTND are 10.0(±0.2) × 10−6 K−1 for Ti2AlN and 13.4(±0.3) × 10−6 K−1 for Cr2GeC.

Temperature-dependent synthesis, crystal structures, characterizations, and DFT calculations of two new copper(II) complexes with p-fluorobenzoic acid and 2,2′-bipyridine ligands

Two new copper(II) complexes, [Cu(p-FBA)2(2,2′-bpy)]·(H2O) (1) and [Cu(p-FBA)(2,2′-bpy)2]·(p-FBA)2 (2) {p-FBA = p-fluorobenzoic acid, 2,2′-bpy = 2,2′-bipyridine} have been obtained from an identical starting mixture using temperature as the only independent variable and characterized by X-ray single crystal diffraction as well as with infrared spectroscopy, elemental analysis, and thermogravimetric analysis. The results reveal that 1 has 1D infinite chain structure formed by O–H···O hydrogen bonds, while 2 features a 0D structure. Additionally, there exist C–H···O hydrogen bonds and π–π stacking interactions in 1, forming 2D supramolecular structure. Furthermore, density functional theory (DFT) calculations of the structures, stabilities, orbital energies, composition characteristics of some frontier molecular orbitals and Mulliken charge distributions of the [Cu(p-FBA)2(2,2′-bpy)] of 1 and [Cu(p-FBA)(2,2′-bpy)2]+ cation of 2 were performed by means of Gaussian 03W package and taking B3LYP/lanl2dz basis set.

Cation solvation in the solid state – temperature-dependent crystal structures in some metal perchlorates solvated by dimethylsulfoxide

Problems arising from the extensive disorder characteristic of the crystalline lattice of dmso solvates of metal perchlorates at room temperature can in many cases be ameliorated or removed at `low' temperature. Present studies of several M(ClO 4) n · 6dmso ( n=2,3) species and Dy(ClO 4) 3 · 8dmso have allowed detailed definition of several homoleptic dmso-solvated metal cations, all of which contain dmso as an O-bound unidentate ligand and which appear to closely confirm the forms of solvated cations deduced from independent solution studies.