| 1. |
- Alammar, Tarek, et al.
(författare)
-
The Power of Ionic Liquids : Crystal Facet Engineering of SrTiO3 Nanoparticles for Tailored Photocatalytic Applications
- 2021
-
Ingår i: Advanced Sustainable Systems. - : Wiley. - 2366-7486. ; 5:2
-
Tidskriftsartikel (refereegranskat)abstract
- Sonochemical synthesis of nano-sized SrTiO3 carried out at close to room temperature, in ionic liquids (ILs) allows the tuning of particle size and particle morphology, that is, tracht and habitus, as well as particle aggregation via the choice of the ionic liquids (ILs) as the reaction medium. The nanoparticles demonstrate high performance for photocatalytic water splitting and photodecomposition of organic material. To this end bis(trifluoromethanesulfonyl)amide ([Tf2N](-))-based ILs with cations of different properties with respect to specific interactions with the target material are investigated. Isolated, 15 +/- 1 nm sized nano-spheres of SrTiO3 are observed to form in [C(3)mimOH][Tf2N] ([C(3)mimOH](+) = 1-(3-hydroxypropyl)-3-methylimidazolium). Aggregation of small sized nanoparticles are observed to around 250 +/- 100 nm large cube-like formations in [C(4)mim][Tf2N] ([C(4)mim](+) = 1-butyl-3-methylimidazolium), raspberry-like in [C4Py][Tf2N] ([C4Py](+) butylpyridinium), and ball-like in [P-66614][Tf2N] ([P-66614](+) tetradecyltrihexyl phosphonium). Importantly, the different materials show different performance as photocatalysts. SrTiO3 prepared in [C(4)mim][Tf2N] shows the highest photocatalytic activity for H-2 evolution (1115.4 mu mol h(-1)) when using 0.025 wt% Rh as the co-catalyst, whereas the material prepared in [C(3)mimOH][Tf2N] shows the highest activity for the photocatalytic degradation of methylene blue (88%) under UV irradiation. The different photocatalytic activities can be correlated with the different crystal surface facets expressed in the respective nanosized SrTiO3 material, {110} for material obtained from [C(4)mim][Tf2N], and {100} for material from [C(3)mimOH][Tf2N]. First-principles density functional theory (DFT) calculations are used to support the experimental findings.
|
|
| 2. |
- Babizhetskyy, V., et al.
(författare)
-
Investigation in the ternary Ta-Ni-P system : Solid state phase equilibria at T=1070 K, crystal and electronic structures of new ternary phosphides
- 2021
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 864
-
Tidskriftsartikel (refereegranskat)abstract
- The solid state phase diagram for the ternary Ta-Ni-P system was established at T=1070 K in the region of up to 67 at% of P by means of X-ray powder diffraction methods (PXRD). Six ternary compounds, namely Ta4NiP (Nb4CoSi-type), Ta1.10-0.82Ni0.90-1.18P (TiNiSi-type), TaNiP2 (NbNiP2-type), Ta(5.00-4.81)Ni(4.00-4.19)P4 (Nb5Cu4Si4-type), TaNi2P (own structure type) and Ta1-0.08(1)Ni0.08(1)P2 (OsGe2-type) have been confirmed to exist. Rather minor Ta/Ni homogeneity ranges have been found for alpha-Ta3-xNixP (x=0.2) (Ti3P-type), Ta1-xNixP (x=0.18) (NbAs-type), Ni3-xTaxP (x=0.2) (Ni3P-type) and Ni2-xTaxP (x=0.25) (Fe2P-type). The crystal structure of Ta4.811(9)Ni4.189(9)P4 has been refined from single crystal X-ray diffraction data (Nb5Cu4Si4-type, space group I4/m, a =9.8474(17), c=3.5182(7) angstrom, R1=0.0283, wR2=0.0470), while that of the new TaNi2P compound was determined by means of PXRD. This phosphide crystalizes in its own structure type (space group Pnma, a=8.3588(3), b=3.5208(1), c=6.7051(3) angstrom, R-I=0.044, R-P=0.161). A new isostructural Fe-compound, TaFe2P (a=8.358(2), b=3.5194(7), c=6.703(1) angstrom), was also synthetized. The electronic structures of Ta5Ni4P4 and TaNi2P were analyzed using the tight-binding linear muffin-tin orbital (TB-LMTO) and extended Huckel methods.
|
|
| 3. |
- Babizhetskyy, Volodymyr, et al.
(författare)
-
New intermetallics R1+xZr1−xNi (R = Er–Tm, x ~ 0.5) with the TiNiSi type of structure
- 2021
-
Ingår i: Intermetallics (Barking). - : Elsevier BV. - 0966-9795 .- 1879-0216. ; 137
-
Tidskriftsartikel (refereegranskat)abstract
- A new series of isostructural rare earth compounds R1+xZr1−xNi (R = Er, Tm, Lu; x ~ 0.5) was synthesized from the elements by arc melting and subsequent annealing at 870 K for 1400 h. The crystal structures of the intermetallic compounds were investigated by means of single-crystal X-ray diffraction. They all crystallize in the TiNiSi structure type (space group Pnma, No. 62, oP12). In R1+xZr1−xNi, the R/Zr statistical mixture leading to nonequiatomic compositions occupies the position corresponding to the nickel site of the TiNiSi structure type. The calculated shortest interatomic distances are close to the sums of the single-bond covalent radii of respective elements. Electronic structure calculations performed with the tight-binding LMTO method revealed the non-zero density of states at the Fermi level and suggest metallic character. R1+xZr1−xNi (R = Er, Tm, Lu; x ~ 0.5) undergoes no long-range magnetic ordering down to 2 K.
|
|
| 4. |
- Bousrez, Guillaume, et al.
(författare)
-
Ionic Liquid-Based Dye-Sensitized Solar Cells-Insights into Electrolyte and Redox Mediator Design
- 2021
-
Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 9:24, s. 8107-8114
-
Tidskriftsartikel (refereegranskat)abstract
- A series of asymmetric and symmetric 1,3-dialkyltriazolium iodides were studied with hindsight to their application as electrolytes and redox mediators in dye-sensitized solar cells (DSSCs). Compounds with an alkyl chain length from C4 to C10 present the characteristics of ionic liquids (ILs), whilst those with longer chains exhibit liquid crystallinity. All compounds show an appreciable chemical and thermal stability with decomposition temperatures around 185–195 °C. Testing these compounds as electrolytes and redox mediators in DSSCs reveals significant changes in the properties of the electrolyte upon addition of the redox couple. Addition of iodine generally leads to a depression of the melting point and an enhancement of conductivity. These changes in the electrolyte, which are significant, have so far been largely overlooked in DSSC optimization. Furthermore, in comparison to frequently employed imidazolium iodides, 1-alkyl-3-methyltriazolium iodides show both an improved superior efficiency and an extended cell lifetime. This is attributed to the fact that, unlike the imidazolium salts, the triazolium counterparts are not hygroscopic. The nonhygroscopic nature of the salts also renders device fabrication easier. In addition, electrode passivation, which is commonly observed with imidazolium iodides, could not be noticed for the triazolium analogues, making these materials overall extremely attractive.
|
|
| 5. |
- Bousrez, Guillaume, et al.
(författare)
-
Magnetic, Photo- and Electroluminescent : Multifunctional Ionic Tb Complexes
- 2021
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:23, s. 17487-17497
-
Tidskriftsartikel (refereegranskat)abstract
- In the search for new multifunctional materials, particularly for application in solid-state lighting, a set of terbium salicylato (Sal) complexes of general composition [Cat][Tb(Sal)4] with the commonly ionic liquid-forming (IL) cations [Cat] = (2-hydroxyethyl)trimethylammonium (choline) (Chol+), diallyldimethylammonium (DADMA+), 1-ethyl-3-methylimidazolium (C2C1Im+), 1-butyl-3-methylimidazolium (C4C1Im+), 1-ethyl-3-vinylimidazolium (C2Vim+), and tetrabutylphosphonium (P4444+) were synthesized. All Tb compounds exhibit strong green photoluminescence of high color purity by energy transfer from the ligand in comparison with what the analogous La compounds show, and quantum yields can reach up to 63% upon ligand excitation. When excited with an HF generator, the compounds show strong green electroluminescence with the same features of mission. The findings promise a high potential of application as emitter materials in solid-state lighting. As an additional feature, the Tb compounds show a strong response to applied external fields, rendering them multifunctional materials.
|
|
| 6. |
- Bousrez, Guillaume, et al.
(författare)
-
Ready Access to Anhydrous Anionic Lanthanide Acetates by Using Imidazolium Acetate Ionic Liquids as the Reaction Medium
- 2021
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 27:52, s. 13181-13189
-
Tidskriftsartikel (refereegranskat)abstract
- Access to lanthanide acetate coordination compounds is challenged by the tendency of lanthanides to coordinate water and the plethora of acetate coordination modes. A straightforward, reproducible synthetic procedure by treating lanthanide chloride hydrates with defined ratios of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C(2)mim][OAc]) has been developed. This reaction pathway leads to two isostructural crystalline anhydrous coordination complexes, the polymeric [C(2)mim](n)[{Ln(2)(OAc)(7)}(n)] and the dimeric [C(2)mim](2)[Ln(2)(OAc)(8)], based on the ion size and the ratio of IL used. A reaction with an IL : Ln-salt ratio of 5 : 1, where Ln=Nd, Sm, and Gd, led exclusively to the polymer, whilst for the heaviest lanthanides (Dy-Lu) the dimer was observed. Reaction with Eu and Tb resulted in a mixture of both polymeric and dimeric forms. When the amount of IL and/or the size of the cation was increased, the reaction led to only the dimeric compound for all the lanthanide series. Crystallographic analyses of the resulting salts revealed three different types of metal-acetate coordination modes where eta(2)mu kappa(2) is the most represented in both structure types.
|
|
| 7. |
- Kelley, Steven P., et al.
(författare)
-
Structural analysis of mono-substituted N-butyl-pyridinium salts : in search of ionic liquids
- 2021
-
Ingår i: Journal of coordination chemistry (Print). - : Informa UK Limited. - 0095-8972 .- 1029-0389. ; 74:1-3, s. 117-128
-
Tidskriftsartikel (refereegranskat)abstract
- Four mono-substituted N-butylpyridinium salts, 1-butyl-4-dimethylaminopyridinium chloride [b4dmapy]Cl, 1-butyl-4-methylpyridinium bromide [b4mpy]Br, 1-butyl-4-methylpyridinium hexafluorophosphate [b4mpy][PF6], and 1-butyl-3-methylpyridinium hexafluorophosphate [b3mpy][PF6] were synthesized and characterized using single crystal X-ray diffraction. The crystal structures were examined with the intent of identifying ion interactions leading to higher melting points of the halide salts with respect to the [PF6]– salts. The changes in hydrogen bonding, C–H⋅⋅⋅π, and van der Waals interactions have been analyzed with respect to anion, functional groups, and the symmetry of the cation to establish interdependence with the compound’s physicochemical properties. It has been observed that the cation–anion interactions are represented by highly directional hydrogen bonds and show strong preference to positions of interaction depending on the anion. The cations of the halide salts show strong tendency towards higher dimensional formations, while those of the [PF6]– salts prefer low dimensional assemblies both being based mainly on the weaker van der Waals interactions. These interactions depend on the shape of the cation but may offer certain structure-ordering rigidity accommodating variable anions.
|
|
| 8. |
- Kotur, B., et al.
(författare)
-
Crystal and electronic structures of the new ternary silicide Sc12Co41.8Si30.2
- 2021
-
Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 302
-
Tidskriftsartikel (refereegranskat)abstract
- Sc12Co41.8Si30.2 was prepared from the elements by arc melting under argon and subsequent tempering at 800 °C for 350 h. Single-crystal X-ray diffraction reveals Sc12Co41.8Si30.2 to crystallize in a new hexagonal structure type: Pearson's symbol (PS) hP168, space group P6/mmm, a = 17.291(1), c = 8.0293(8) Å. The crystal structure is formed of three types of atomic layers along the [001] direction – two flat at z = 0 and z = 0.5 and one corrugated at z = 0.16–0.33 and z = 0.67–0.84, shows a substantial degree of positional and occupational disorder and close structural relationships to a series of hexagonal structures with PS hP164–hP171. Quantum chemical calculations have been performed to analyze the electronic structure and provide deeper insight into the structure-property relationships. The quantum chemical calculation indicates that the material features both two-center, two-electron localized bonding and multi-center multi-electron delocalized bonding.
|
|
| 9. |
- Leu, Meike, et al.
(författare)
-
Synthesis of luminescent semiconductor nanoparticles in ionic liquids -the importance of the ionic liquid in the formation of quantum dots
- 2021
-
Ingår i: Green Chemistry Letters and Reviews. - : Informa UK Limited. - 1751-8253 .- 1751-7192. ; 14:1, s. 128-136
-
Tidskriftsartikel (refereegranskat)abstract
- Zinc sulfide (ZnS) and cadmium sulfide (CdS) nanoparticles were synthesized in different ionic liquids (IL) with microwave irradiation. Particle characterization by means of powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and optical spectroscopy (UV-vis absorption and photoluminescence) showed a strong dependence of the particle size depending on the IL employed. Whilst all ILs yielded particles in the nanometer regime and showed in their optical properties quantum confinement, particularly small particles were obtained from choline-base ILs pointing to the strong influence of this IL cation in blocking the particle growth. Here, quantum dots of 1.5–3 nm size were yielded for both, ZnS and CdS.
|
|
| 10. |
- Nayak, Amrita, et al.
(författare)
-
Anhydrous vs Hydrated f-Element Acetate Polymers Dictated by the Stoichiometry of Protic Acidic/Basic Azole Mixtures
- 2021
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 21:4, s. 2516-2525
-
Tidskriftsartikel (refereegranskat)abstract
- Continuing our investigations of ionic liquid (IL) based routes to a library of f-element/soft donor complexes which could be studied crystallographically, we have explored the dissolution of f-element salts in protic imidazole-based ILs containing only soft donors at high temperatures to drive off volatiles, including water and carboxylic or mineral acids. Here we present our results, reacting acidic and basic azoles in 1:3 or 1:1 stoichiometric compositions at elevated temperature, followed by saturation with Nd(OAc)(3)center dot xH(2)O or Ce(OAc)(3)center dot xH(2)O, which led to 13 new metal-acetate polymeric complexes identified by single-crystal X-ray diffraction. We found that the diversity in coordination modes of the simple acetate ligand that interfere with substitution of the softer N donors led to several readily crystallizable complexes forming two distinct groups with respect to f-element interaction with the ionic liquid precursors. When the acidic/basic azole ratio was 1:3, acetate and a neutral basic azole were found to be coordinated to the metal centers but no water, although in one case (2) water was observed in the secondary coordination sphere: [Ce(mu(2)-OAc)(3)(C(1)im)](n) (1, C(1)im = 1-methylimidazole), [Nd(mu(2)-(OAc)(3)(C(1)im)](n)center dot nH(2)O (2), [Ce(mu(2)-OAc)(3)(C(2)im)](n) (3, C(2)im = 1-ethylimidazole), [Ln(mu(2)-OAc)(3)DMF](n) (Ln = Nd (4), Ce (5); dimethylformamide (DMF) was substituted for the azole mixture), and [Nd(mu(2)-OAc)(3)(C(4)im)](n) (6, C(4)im = 1-butylimidazole). However, when the stoichiometric ratio was 1:1, water was always observed coordinated to the metal ions with the acidic azole included in the structure as a solvate or cocrystal, despite a higher reaction temperature: [Nd(mu(2)-OAc)(3)(OH2)](n)center dot n(1,2,3-Taz) (7,1,2,3-Taz = 1,2,3-triazole), [Ln(mu(2)-OAc)(3)(OH2)](n)center dot n(4,5-DCim) (Ln = Nd (8), Ce (9), 4,5-DCim = 4,5-dicyanoimidazole), [Ln(mu(2)-OAc)(3)(OH2)](n)center dot n(3,5-diNH(2)-1,2,4-Taz) (Ln = Nd (10), Ce (11), 3,5diNH(2)-1,2,4-Taz = 3,5-diamino-1,2,4-triazole), [Ce(mu(2)-OAc)(3)(OH2)](n)center dot n(3-NH2-1,2,4-Taz) (12, 3-NH2-1,2,4-Taz = 3-amino-1,2,4-triazole), and [Nd(mu(2)-OAc)(3)(OH2)](n)center dot n(5-NH2-Tz) (13, 5-NH2-Tz = 5-aminotetrazole). All of the compounds retain the Ln:OAc- ratio of 1:3 and form 1D polymeric chains; however, they exhibit a variety of coordination modes affecting the degree of chain condensation. The isolation of both hydrated and anhydrous products revealed different abilities of the investigated soft N-donors to compete with O-donors finding their place in the coordination sphere of the lanthanide or in the crystal lattice.
|
|
| 11. |
- Ovchinnikov, Alexander, et al.
(författare)
-
Overlooked Binary Compounds Uncovered in the Reinspection of the La-Au System : Synthesis, Crystal Structures, and Electronic Properties of La7Au3, La3Au2, and La3Au4
- 2021
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:16, s. 12158-12171
-
Tidskriftsartikel (refereegranskat)abstract
- Although compound formation between two elements is well studied, thorough investigations make it possible to uncover new binary compounds. A re-examination of the La-Au system revealed three new phases, which were characterized with respect to their structural and electronic properties as well as thermal stability: La7Au3 (Th7Fe3 type, space group P6(3)mc, Pearson code hP20) appears to be metastable. It can be obtained by slow crystallization from a stoichiometric melt. La3Au2 (U3Si2 type, space group P4/mbm, Pearson code tP10) is stable up to 1013 K, where it decomposes peritectically. La3Au, (Pu3Pd4 type, space group R (3) over bar, Pearson code hR14) is thermally stable up to at least 1273 K. In addition, the crystal structures of La2Au(anti-PbCl2 type, space group Pnma, Pearson code oP12) and alpha-LaAu (FeB type, space group Pnma, Pearson code oP8) could be determined by single-crystal X-ray diffraction. The electronic structures and chemical bonding have been evaluated from first principles calculations. They show that all compounds can be viewed as electron-rich, polar intermetallics.
|
|
| 12. |
- Pakhira, Santanu, et al.
(författare)
-
Short-range ferromagnetic order due to Ir substitutions in single-crystalline Ba(Co1−xIrx)2As2 (0 ≤ x ≤ 0.25)
- 2021
-
Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 33:11
-
Tidskriftsartikel (refereegranskat)abstract
- The ternary-arsenide compound BaCo2As2 was previously proposed to be in proximity to a quantum-critical point where long-range ferromagnetic (FM) order is suppressed by quantum fluctuations. Here we report the effect of Ir substitutions for Co on the magnetic and thermal properties of Ba(Co1-xIrx)(2)As-2 (0 <= x <= 0.25) single crystals. These compositions all crystallize in an uncollapsed body-centered-tetragonal ThCr2Si2 structure with space group I4/mmm. Magnetic susceptibility measurements reveal clear signatures of short-range FM ordering for x > 0.11 below a nearly composition-independent characteristic temperature T-cl approximate to 13 K. The small variation of T-cl with x, thermomagnetic irreversibility between zero-field-cooled and field-cooled magnetic susceptibility versus T, the occurrence of hysteresis in magnetization versus field isotherms at low field and temperature, and very small spontaneous and remanent magnetizations mu(B)/f.u. together indicate that the FM response arises from short-range FM ordering of FM spin clusters as previously inferred to occur in Ca(Co1-xIrx)(2-y)As-2. Heat-capacity C-p(T) data do not exhibit any clear feature around T-cl, consistent with the very small moments of the FM clusters. The C-p(T) in the paramagnetic temperature regime 25-300 K is well described by the sum of a Sommerfeld electronic contribution and Debye and Einstein lattice contributions where the latter lattice contribution suggests the presence of low-frequency optic modes associated with the heavy Ba atoms in the crystals.
|
|
| 13. |
- Pakhira, Santanu, et al.
(författare)
-
Suppression of antiferromagnetic order and strong ferromagnetic spin fluctuations in Ca(Co1−xNix)2−yAs2 single crystals
- 2021
-
Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 104:9
-
Tidskriftsartikel (refereegranskat)abstract
- CaCo2−yAs2 is a unique itinerant system having strong magnetic frustration. Here, we report the effect of electron doping on the physical properties resulting from Ni substitutions for Co. The single crystals of Ca(Co1−xNix)2−yAs2 were characterized by single-crystal x-ray diffraction, energy-dispersive x-ray spectroscopy, magnetization M versus temperature T, magnetic field H, time t, and heat capacity Cp(H,T) measurements. The A-type antiferromagnetic (AFM) transition temperature TN=52 K for x=0 decreases to 22 K with only 3% Ni substitution and is completely suppressed for x>0.16. For 0.11≤x≤0.52 strong ferromagnetic (FM) fluctuations develop as revealed by magnetic susceptibility χ(T)=M(T)/H measurements. For x=0.11 and 0.16 competing AFM and FM interactions result in a reentrant spin-glass behavior below TN, as evidenced by the observations of thermomagnetic hysteresis and magnetic relaxation. Enhanced FM fluctuations are also found for the x=0.21 and 0.31 crystals, where χc increases significantly at low T. A large χ anisotropy in these compositions where χc is up to a factor of two larger than χab suggests that the FM spin fluctuations are quasi-1D in nature. Weak ferromagnetic contributions to the magnetization are found at T=2 K for x=0.11–0.31. Heat-capacity Cp(T) measurements reveal the presence of FM quantum spin fluctuations for 0.11≤x≤0.52, where a logarithmic T dependence of Cp(T)/T is observed at low T. The suppression of AFM order by the development of strong FM fluctuations in Ca(Co1−xNix)2−yAs2 crystals suggests the presence of a FM quantum-critical point at x≈0.20. Our density-functional theory (DFT) calculations confirm that FM fluctuations are enhanced by Ni substitutions for Co in CaCo2−yAs2. The Sommerfeld electronic heat-capacity coefficient is enhanced for x=0, 0.21, and 0.42 by about a factor of two compared to DFT calculations of the density of states (DOS) at the Fermi energy, suggesting an enhancement of the DOS from electron-phonon and/or electron-electron interactions. The crystals with x>0.52 do not exhibit FM spin fluctuations or magnetic order at T≥1.8 K, which was found from the DFT calculations to arise from a Stoner transition. Superconductivity is not observed above 1.8 K for any of the compositions. Neutron-diffraction studies of crystals with x=0.11 and 0.16 in the crossover regime (0.1≲x≲0.2) show no evidence of A-type ordering as observed in the parent compound with x=0. Furthermore, no other common magnetic structures, such as ferromagnetic (FM), helical stacking of in-plane FM layers, or in-plane AFM structure, are found with an ordered moment greater than the uncertainty of 0.05μB per transition-metal atom.
|
|
| 14. |
- Ponou, Siméon, et al.
(författare)
-
Uncovering new transition metal Zintl phases by cation substitution : the crystal chemistry of Ca3CuGe3 and Ca2+nMnxAg2-x+zGe2+n-z (n=3, 4)
- 2021
-
Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 23:14, s. 2711-2722
-
Tidskriftsartikel (refereegranskat)abstract
- High-temperature solid-state reactions of the respective elements afforded the new transition metal Zintl phases Ca3CuGe3 (Sc3NiSi3 type, monoclinic C2/m - i(7), Pearson code mC28), Ca6MnxAg2-x+zGe6-z (own type, monoclinic P2(1)/m - e(14), Pearson code mP28) and, Ca5MnxAg2-x+zGe5-z (Ca5MgAgGe5 type, orthorhombic Pnma - c(12), Pearson code oP48) as evidenced by single-crystal X-ray diffraction. They are additional representatives of the recently discovered homologous series Ca2+nM2+zGe2+n-z, already reported with M = Ag, Mg. These new phases were rationally prepared, after speculation that Cu and Mn could replace the isovalent Ag and Mg, respectively, to yield isostructural phases. Their crystal chemistry is discussed using established 'structure directing rules'. Their structures are best described according to the Zintl-Klemm formalism as (Ca2+)((2+n))[M2+zGe2+n-z)](2(2+n)-) featuring (poly-)germanide oligomers, [Ge-n]((2n+2)-) with n = 1-5. These Zintl anions interact with the highly polarizing small M (Cu, Ag, Mn) cations through their terminal Ge atoms, while the central Ge atoms are in trigonal prismatic coordination with the active metal Ca. Electronic structure calculations using density functional theory (DFT) were conducted on the idealized fully ordered model of Ca3MGe3 (Sc3NiSi3 type) with M = Cu, Ag for an analysis of the chemical bonding and structure stabilizing factors. Our findings suggest that new transition metal Zintl phases can be obtained through partial to complete replacement of the highly polarizing small s-block cations (Li, Mg) in the Ca-(Li,Mg)-(Ge,Si) system by their isovalent transition metals like Ag, Cu, and Mn. However, due to differences in coordination requirements and possible strong metal-metal bonding between the d-block elements, the resulting transition metal phases may not be isostructural with their Li and Mg counterparts, even when featuring the same type of Zintl anions.
|
|
| 15. |
- Provino, Alessia, et al.
(författare)
-
Crystal and Magnetic Structures of the Ternary Ho2Ni0.8Si1.2 and Ho2Ni0.8Ge1.2 Compounds : An Example of Intermetallics Crystallizing with the Zr2Ni1–xP Prototype
- 2021
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:21, s. 16397-16408
-
Tidskriftsartikel (refereegranskat)abstract
- We report two new rare-earth (R) ternary intermetallic compounds—Ho2Ni0.8T1.2 with T = Si and Ge—that correspond to the R5Ni2T3 phase earlier reported to form in Dy–Ni–T and Ho–Ni–T ternary systems. The compounds crystallize in a filled version of the orthorhombic Zr2Ni1–xP-type structure with x = 0.52; their stoichiometry, determined from both single-crystal and powder X-ray diffraction data, is centered on Ho2Ni0.8T1.2 with a narrow solid solubility range for the silicide, while the germanide appears to be a line phase. In addition to R = Dy and Ho, R2Ni0.8T1.2 compounds also form for R = Y and Tb, representing the first examples of rare-earth-based compounds adopting the Zr2Ni1–xP structural prototype. Bulk magnetization data reveal the main transitions of the ferrimagnetic or ferromagnetic type at TC = 38 K for Ho2Ni0.8Si1.2 and TC = 37 K for Ho2Ni0.8Ge1.2, which are followed by subsequent magnetic reordering at lower temperatures. Neutron diffraction shows complex magnetic structures below TC with both ferromagnetic and antiferromagnetic components and magnetic propagation vector κ1 = [0, 0, 0]. Below TN ≅ 24 K (22 K) for the silicide (germanide), an additional antiferromagnetic coupling following an incommensurate magnetic propagation vector κ2 = [κx, 0, 0] appears to coexist with the first magnetic structure.
|
|
| 16. |
- Renier, Olivier, et al.
(författare)
-
Developing design tools for introducing and tuning structural order in ionic liquids
- 2021
-
Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 23:8, s. 1785-1795
-
Tidskriftsartikel (refereegranskat)abstract
- Ionic liquids (ILs) are receiving growing interest as highly tunable, multifunctional materials. Remarkably for liquids, they tend to display a high level of structural order. This structural order may even lead to the formation of mesophases such as liquid crystals (LCs). Imidazolium compounds are by far the most popular ILs, because they offer a widely versatile platform for property tuning. To investigate what is driving structural order in imidazolium-based ILs a series of asymmetrical 1-dodecyl-2-methyl-3-alkylimidazolium bromides, [C(12)C(1)C(n)im][Br] with n = 0-12 have been synthesized, fully characterized and their structures and properties compared with the analogous 1-dodecyl-3-alkylimidazolium as well as the 1,2,3-triazolium bromides. The aim is to examine the influence of the replacement of the most acidic 2-H proton on the imidazolium head group by methylation on the properties and structure of ILs. For all compounds, except for compounds with butyl- and hexyl-chains as well as the protonated species, mesophase formation can be observed. Obviously, the simple presence of long alkyl chains such as dodecyl (a design concept frequently put forward in the literature) is not sufficient to support mesophase formation alone. Rather, for the formation of a liquid crystalline phase, a balance between attractive van der Waals forces, hydrogen bonds, and electrostatic interactions is required. Data from temperature-dependent small-angle X-ray scattering (SAXS) and polarizing optical microscopy (POM) suggest three different cation conformations for the studied [C(12)C(1)C(n)im][Br]: cations with 0 <= n <= 4 exhibit a near-linear conformation; for 5 <= n <= 10 a V-shape is adopted, and for n = 11 or 12 a U-shape is found. We demonstrated that the structural possibility for an interdigitation of the long chains is an influential factor for the formation of a mesophase.
|
|
| 17. |
- Renier, Olivier, et al.
(författare)
-
Shape Preserving Single Crystal to Amorphous to Single Crystal Polymorphic Transformation Is Possible
- 2021
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:48, s. 20202-20206
-
Tidskriftsartikel (refereegranskat)abstract
- Many crystalline materials form polymorphs and undergo solid–solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl2(1,3-diethylimidazole-2-thione)2 which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms.
|
|
| 18. |
- Sangeetha, N. S., et al.
(författare)
-
First-order antiferromagnetic transitions of SrMn2P2 and CaMn2P2 single crystals containing corrugated-honeycomb Mn sublattices
- 2021
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 118:44
-
Tidskriftsartikel (refereegranskat)abstract
- SrMn2P2 and CaMn2P2 are insulators that adopt the trigonal CaAl2Si2-type structure containing corrugated Mn honeycomb layers. Magnetic susceptibility χ and heat capacity versus temperature T data reveal a weak first-order antiferromagnetic (AFM) transition at the Néel temperature TN=53(1) K for SrMn2P2 and a strong first-order AFM transition at TN=69.8(3) K for CaMn2P2. Both compounds exhibit isotropic and nearly T-independent χ(T≤TN), suggesting magnetic structures in which nearest-neighbor moments are aligned at ≈120° to each other. The 31P NMR measurements confirm the strong first-order transition in CaMn2P2 but show critical slowing down above TN for SrMn2P2, thus also evidencing second-order character. The 31P NMR measurements indicate that the AFM structure of CaMn2P2 is commensurate with the lattice whereas that of SrMn2P2 is incommensurate. These first-order AFM transitions are unique among the class of (Ca, Sr, Ba)Mn2 (P, As, Sb, Bi)2 compounds that otherwise exhibit second-order AFM transitions. This result challenges our understanding of the circumstances under which first-order AFM transitions occur.
|
|
| 19. |
- Smetana, Volodymyr, et al.
(författare)
-
Sandwiched Kagomé Lattices in a Coordination Polymer Based on Mixed-Valent Uranium
- 2021
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 21:3, s. 1727-1733
-
Tidskriftsartikel (refereegranskat)abstract
- The metal-organic material (UO)-O-V((UO2)-O-VI)(2)(OH)(5)-(Triaz)(2) (Triaz = 1,2,4-triazolate) has been isolated from the reaction of UO2(NO3)(2)center dot 6H(2)O with 1,2,4-triazole in the ionic liquid 1-ethyl-3-methylimidazolium acetate ([C(2)mim][OAc]). The compound's crystal structure is comprised of planar inorganic layers interconnected by organic linkers into a 3D framework. These layers represent a uranium-based coordination polymer with a Kagome topology that to the best of our knowledge has never been recognized in f-element coordination chemistry.
|
|
