Volodymyr Smetana

Volodymyr Smetana


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Works at Department of Materials and Environmental Chemistry
Visiting address Svante Arrhenius väg 16 C
Room C522
Postal address Institutionen för material- och miljökemi 106 91 Stockholm


A selection from Stockholm University publication database
  • 2020. Volodymyr Smetana (et al.). Science Advances 6 (5)

    Aperiodic formations continue to focus interest in areas ranging from advanced scientific theories to practical everyday applications. Starting from diverse and tightly bonded intermetallic compounds, this world showed an important breakthrough toward the so-called soft systems of meso/macroscale: liquid crystals, thin films, polymers, proteins, etc. This work opens a route for making bulk quasicrystals (QC) in an unprecedented but very common area, with molecular ligands. Since these systems are, to a large extent, transparent, they extend the possible areas of QC application to previously unreachable corners, e.g., photonics. We combined efficient bridging ligands with uranyl pentagonal bonding centers and, unexpectedly, brought the unique attributes of f-element coordination chemistry to an interdisciplinary area of aperiodic formations. Taking advantage of the planar coordination of uranyl ions, we were able to direct the structure expansion solely in two directions with a characteristic snub square tiling, a predicted but previously unobtainable dodecagonal approximant.

  • 2020. Alexander Ovchinnikov, Volodymyr Smetana, Anja-Verena Mudring. Journal of Physics 32 (24)

    Complex metallic alloys belong to the vast family of intermetallic compounds and are hallmarked by extremely large unit cells and, in many cases, extensive crystallographic disorder. Early studies of complex intermetallics were focusing on the elucidation of their crystal structures and classification of the underlying building principles. More recently, ab initio computational analysis and detailed examination of the physical properties have become feasible and opened new perspectives for these materials. The present review paper provides a summary of the literature data on the reported compositions with exceptional structural complexity and their properties, and highlights the factors leading to the emergence of their crystal structures and the methods of characterization and systematization of these compounds.

  • 2019. Volodymyr Smetana, Magdalena Wilk-Kozubek, Anja-Verena Mudring. Crystal Growth & Design 19 (9), 5429-5440

    Materials showing thermoelectric properties known as thermoelectrics can reversibly convert a temperature gradient into electricity. Since the vast majority of energy we use comes from thermal processes or creates thermal energy as waste energy, the search for materials able to efficiently convert thermal energy is of extreme importance. The discovery of a new, highly efficient thermoelectric material is complicated due to the special requirements imposed on the combination of electrical and thermal transport properties. Metal chalcogenides (MCs) have attracted significant attention as high performance thermoelectric materials. Their subgroup, active-transition-metal chalcogenides, shows structural and compositional diversity, including a wide occurrence of low-dimensional structural motifs, which opens up a fruitful area for explorations. This area has been preliminarily explored from both structural and functional viewpoints revealing very promising directions and unique compounds. Nevertheless, systematic investigations on transport properties are still missing. Available data suggests the presence of low bandgap semiconductors satisfying at least one of the conditions for a good thermoelectric, whereas the potential for structural and electronic variation in the form of active metal doping and substitution leaves a decent chance to uncover a candidate with acceptably low thermal conductivity and subsequently high thermoelectric performance.

  • 2017. Volodymyr Smetana (et al.). Accounts of Chemical Research 50 (11), 2633-2641

    The design of new materials with desired chemical and physical characteristics requires thorough understanding of the underlying composition structure property relationships and the experimental possibility of their modification through the controlled involvement of new components. From this point of view, intermetallic phases, a class of compounds formed by two or more metals, present an endless field of combinations that produce several chemical compound classes ranging from simple alloys to true ionic compounds. Polar intermetallics (PICs) belong to the class that is electronically situated in the middle, between Hume-Rothery phases and Zintl compounds and possessing e/a (valence electron per atom) values around 2. In contrast to the latter, where logical rules of formation and classification systems were developed decades ago, polar intermetallics remain a dark horse with a huge diversity of crystal structures but unclear mechanisms of their formation. Partial incorporation of structural and bonding features from both nonpolar and Zintl compounds is commonly observed here. A decent number of PICs can be described in terms of complex metallic alloys (CMAs) following the Hume-Rothery electron-counting schemes but exhibit electronic structure changes that cannot be explained by the latter. Our research is aimed at the discovery and synthesis of new polar intermetallic compounds, their structural characterization, and investigation of their properties in line with the analysis of the principles connecting all of these components. Understanding of the basic structural tendencies is one of the most anticipated outcomes of this analysis, and systematization of the available knowledge is the initial and most important step.

    In this Account, we focus on a well-represented but rather small section of PICs: ternary intermetallic compounds of gold with electropositive and post-transition metals of groups 12 to 15. The strong influence of relativistic effects in its chemical bonding results in special, frequently unique structural motifs, while at the same time gold participates in common structure types as an ordinary transition element. Enhanced bonding strength leads to the formation and stabilization of complex homo-and heteroatomic clusters and networks that are compositionally restricted to just a few options throughout the periodic table. Because it has the highest absolute electronegativity among metals, comparable to those of some halogens, gold usually plays the role of an anion, even being able to form true salts with the most electropositive metals. We discuss the occurrence of the structure types and show the place of gold intermetallics in the general picture. Among the structures considered are ones as common as AIB(2) or BaAl4 types, in line with the recently discovered diamond-like homoatomic metal networks, formation of local fivefold symmetry, different types of tunneled structures, and more complex intergrown multicomponent structures.

  • 2019. Deepak Chand (et al.).

    Direct quaternization of 1-methyl-1,2,4-triazole with n-alkyl methanesulfonates (alkyl = butyl, octyl, dodecyl) showed to be an atom-economic, convenient, mild, solvent- and halide-free way to obtain 1,2,4-triazolium methanesulfonate ionic liquids in high purity and yield. Subsequent metathesis with lithium bis(trifluoromethanesulfonyl)amide (LiTf2N) allows for a much desired, easy access to halide-free, bis(trifluoromethanesulfonyl)amide ionic liquids. Differential scanning calorimetry confirms that all investigated compounds qualify as ionic liquids (ILs). Moreover, it reveals for 1-methyl-4-n-dodecyl-1,2,4-triazolium methanesulfonate a rather complex thermal behavior involving formation of mesophases. Indeed, polarizing optical microscopy shows oily streaky textures that are characteristic for smectic liquid crystalline phases. Single-crystal X-ray diffraction structure analysis confirms formation of a layered structure. All compounds are photoluminescent. The color of fluorescence at room temperature can be tuned from blue to orange through the length of the alkyl side chain of the cation, the aromatic interactions between the cations, and the anion nature. In addition, at low temperatures (77 K) a close to white phosphorescence with average lifetimes in the millisecond time range can be observed for 1-methyl-4-n-butyl-triazolium methanesulfonate and all of the studied bis(trifluoromethanesulfonyl)amide ILs. All ILs show an appreciable liquidus range and thermal (up to 260-350 degrees C) and electrochemical stability. The presented set of ILs overcomes the sometimes problematic acidity and low stability of imidazolium ILs in basic environment and can be obtained easily in high purity without halide contamination. Overcoming two shortcomings of classical imidazolium ILs, they may be good alternatives for a number of applications and even enabling new ones.

  • 2019. J. Liu (et al.). Journal of Magnetism and Magnetic Materials 474, 482-492

    The kinetic arrest observed in the parent Gd5Ge4 gradually vanishes when a small fraction (x = 0.025, 0.05 and 0.10) of Gd is replaced by Sc in (Gd1-xScx)(5)Ge-4, and the magnetic ground state changes from antiferromagnetic (AFM) to ferromagnetic (FM). A first order phase transition coupled with the FM-AFM transition occurs at T-C = 41 K for x = 0.05 and at T-C = 53 K for x = 0.10 during heating in applied magnetic field of 1 kOe, and the thermal hysteresis is near 10 K. The first-order magnetic transition is coupled with the structural Sm5Ge4-type to Gd5Si4-type transformation. The magnetization measured as a function of applied magnetic field shows sharp metamagnetic-like behavior. At the same time, the AFM to paramagnetic transition in (Gd1-xScx)(5)Ge-4 with x = 0.10, is uncharacteristically broad indicating development of strong short-range AFM correlations above the Ned temperature. Comparison of the magnetization data of bulk, powdered, and metal-varnish composite samples of (Gd0.95Sc0.05)(5)Ge-4 shows that mechanical grinding and fabrication of a composite have little effect on the temperature of the first-order transformation, but short-range ordering and AFM/FM ratio below T-C are surprisingly strongly affected.

  • 2019. N. S. Sangeetha (et al.). Physical Review B 100 (9)

    The Eu(+2 )spins-7/2 in EuNi2As2 with the body-centered tetragonal ThCr2Si2 structure order antiferromagnetically below the Ned temperature T-N = 15 K into a helical antiferromagnetic (AFM) structure with the helix axis aligned along the tetragonal c axis and the Eu ordered moments aligned ferromagnetically within the ab plane as previously reported from neutron diffraction measurements [T. Jin et al., Phys. Rev. B 99, 014425 (2019)]. Here we study the crystallographic, magnetic, thermal, and electronic transport properties of Bi flux grown single crystals using single-crystal x-ray diffraction, anisotropic magnetic susceptibility chi, isothermal magnetization M, heat capacity C-p, and electrical resistivity rho measurements versus applied magnetic field H and temperature T. Vacancies are found on the Ni sites corresponding to the composition EuNi1.95(1)As2. A good fit of the rho(T) data by the Bloch-Grijneisen theory for metals was obtained. The chi(ab )(T) data below T-N are fitted well by molecular field theory (MFT), and the helix turn angle kd and the Eu-Eu Heisenberg exchange constants are extracted from the fit parameters. The kd value is in good agreement with the neutron-diffraction result. The magnetic contribution to the zero-field heat capacity below T-N is also fitted by MFT. The isothermal in-plane magnetization M-ab exhibits two metamagnetic transitions versus H, whereas M-c(T = 2 K) is nearly linear up to H = 14 T, both behaviors being consistent with MFT. The M-c(H, T), rho(H-c, T ), and C-p(H-c, T ) data yielded aH(c)-T phase diagram separating the AFM and paramagnetic phases in good agreement with MFT. Anisotropic chi(T) literature data for the ThCr2Si2-type helical antiferromagnet EuRh2As2 were also fitted well by MFT. A comparison is made between the crystallographic and magnetic properties of ThCr2Si2-type EuM(2)Pn(2) compounds with M = Fe, Co, Ni, Cu, or Rh, and Pn = P or As, where only ferromagnetic and c-axis helical AFM structures are found.

  • 2019. Guangmei Wang (et al.). Chemistry of Materials 31 (18), 7329-7339

    An ionothermal synthesis study of transition metal phosphates using the ionic liquid 1-butyl-4-methylpyridinium hexafluorophosphate [C(4)mpy] [PF6] yielded four new, different open framework manganese compounds, that is, K2Mn3 (HPO4)(2)(PO3F)F-2 (1), (NH4)(2)Mn-3 (HPO4)(2) (PO3F)-F-2 (2), KMn3 (H2PO4)(HPO4)(2)F-2 (3), and (NH4)Mn-3(H2PO4)(PO3F)(2)F-2 (4). The obtained products not only feature new framework topologies unprecedented in the family of phosphates but also interesting properties as the transition metal gives rise to both luminescent (rendering them potential nonrare earth containing red emitting phosphors) and unconventional magnetic properties governed by geometric frustrations. Aside from the structural analysis (powder and single-crystal X-ray diffraction, infrared spectroscopy), a variety of characterization methods (photoluminescence spectroscopy and magnetic measurements) were applied to study the material's properties. Single crystal X-ray studies reveal that 1 (P2(1)/c with a = 5.501(1), b = 14.203(3), c = 16.905(4) angstrom, beta = 108.65(3)degrees, V = 1251.4 angstrom(3), and Z = 4) and 2 (P2(1)/c with a = 5.587(1), b = 14.507(3), c = 17.364(3) angstrom, beta = 108.75(3)degrees, V = 1332.6(5) angstrom(3), and Z = 4) feature S-shaped 18-ring channels along [100], which are formed by trimer-Mn3O9F2 chains parallel to [100] and interconnecting PO3 (OH) and PO3F tetrahedra. The structure of compounds 3 (C2/c with a = 20.307(4), b = 7.635(1), c = 7.834(2) angstrom, beta = 103.26(3)degrees, V = 1182.2(4) angstrom(3), and Z = 4) and 4 (C2/c with a = 20.402(4), b = 7.673(1), c = 7.845(2) angstrom, beta = 103.56(3)degrees, V = 1193.8(4) angstrom(3), and Z = 4) are characterized by layers, which are built of Mn3O8F4 octahedra trimers, with Kagome topology parallel to the be plane featuring 3,6-ring channels. The layers are stacked according to a sequence of AA(i) along the a axis. Taking into account the [P(2)O-3(OH)/P(2)O3F] tetrahedra, the Kagome layers are replenished to a Mn3O2 (HPO4)/Mn3O2 (PO3F) composition, which are interlinked by [P(1)O-2(OH)(2)] forming 10-ring channels parallel to [001]. Charge compensation of the macroanions is achieved by K+ (1 and 3) and (NH4)(+) (2 and 4) cations. At room temperature, compounds 1-4 demonstrate a reddish orange emission ascribed to the spin-forbidden T-4(1g)((4)G) -> (6)A(1g) (S-6) transition of the Mn2+ ions. Upon lowering the temperature to 77 K, the emission of each compound is red-shifted and becomes pure red. Compounds 1 and 2 contain spin trimers with a presumable doubled ground state. The intertrimer magnetic coupling is relatively weak, and small ferrimagnetic domains are possible in 1. The magnetic behavior of 3 and 4 can be considered as antiferromagnetic. This can be understood as their staircase Kagome lattices are distorted, meaning that the intrinsic geometrical frustration is lifted.

  • 2019. Guangmei Wang (et al.). Inorganic Chemistry 58 (19), 13203-13212

    A set of different open framework iron phosphates have been synthesized ionothermally using a task-specific ionic liquid, 1-butyl-4-methylpyridinium hexafluorophosphate, that acts in the synthesis as the reaction medium and mineralizer: (NH4)(2)Fe-2(HPO4)(PO4)Cl2F (1) and K2Fe2(HPO4(PO4)Cl2F (2) exhibit similar composition and closely related structural features. Both structures consist of {Fe-2(HPO4)(PO4)-Cl2F}(2)- macroanions and charge balancing ammonium or potassium cations. Their open framework structure contains layers and chains of corner-linked {Fe(1)O2Cl4} and {Fe(2)F2O4} octahedra, respectively, interconnected by PO4 tetrahedra forming 10-ring channels. KFe(PO3F)F-2 (3) is built up by {Fe[(PO3F)(4/3)F-2/2]}{Fe(PO3F)(2/3) F2/2F2} layers separated by K+ cations. Chains of alternating {FeF2O4} and {FeO2F4} octahedra, which are linear for 1 but undulated for 2, are linked to each other via corner-sharing {PO3F} tetrahedra with the fluorine pointing into the interlayer space. The compounds were characterized by means of single crystal and powder X-ray diffraction, infrared spectroscopy, and magnetic measurements. 1 reveals a strong ground state spin anisotropy with a spin 5/2 state and a magnetic moment of 5.3 mu(B) /Fe3+. Specific heat and magnetic data unveil three magnetic transitions at 95, 50, and 3.6 K. Compound 2 has a very similar crystal structure as compared to 1 but exhibits a different magnetic behavior: a slightly lower magnetic moment of 4.7 mu(B)/Fe3+ and a magnetic transition to a canted antiferromagnetic state below 90 K. Compound 3 exhibits typical paramagnetic behavior close to room-temperature (5.71 mu(B)/Fe3+). There are no clear indications for a phase transition down to 2 K despite strong antiferromagnetic spin-spin interactions; only a magnetic anomaly appears at 50 K in the zero-field cooled data.

  • 2019. N. S. Sangeetha (et al.). Physical Review B 100 (9)

    The compound SrCo2As2 with the body-centered tetragonal ThCr2Si2 structure is known to remain paramagnetic down to a temperature T = 0.05 K, but inelastic neutron scattering studies have shown that both ferromagnetic (FM) and antiferromagnetic (AFM) fluctuations occur in single crystals. Thus it is of interest to study how the magnetism evolves on doping SrCo2As2. Previous work on polycrystalline samples of Sr(Co1-xNix)(2)As-2 indicated the development of AFM order for 0 < x less than or similar to 0.3. Here we studied single crystals of Sr(Co1-xNix)(2)As-2 for 0 < x <= 1 and confirmed the occurrence of AFM order which we deduce to have a c-axis helix structure. We also find evidence for an unusual composition-induced magnetic quantum critical point at x approximate to 0.3 where non-Fermi-liquid types of behavior were revealed by heat capacity and electrical resisitivity measurements at low T. Electron-doped Sr (Co1-xNix)(2)As-2 single crystals with compositions x = 0 to 0.9 were grown out of self-flux and SrNi2As2 single crystals out of Bi flux. The crystals were characterized using single-crystal x-ray diffraction (XRD) at room temperature, and magnetic susceptibility chi (H, T), isothermal magnetization M(H, T), heat capacity C-p (H, T), and electrical resistivity rho(H, T) measurements versus applied magnetic field H and T. The XRD studies show that the system undergoes a continuous structural crossover from the uncollapsed-tetragonal (ucT) structure to the collapsed tetragonal (cT) structure with increasing Ni doping. The chi (T) data show that SrCo2As2 exhibits an AFM ground state almost immediately upon Ni doping on the Co site. Ab initio electronic-structure calculations for x = 0 and 0.15 indicate that a flat band with a peak in the density of states just above the Fermi energy is responsible for this initial magnetic-ordering behavior on Ni doping. The AFM ordering is observed in the range 0.013 <= x <= 0.25 with the ordered moments aligned in the ab plane and with a maximum ordering temperature T-N = 26.5 K at x = 0.10. The Curie-Weiss-like T dependence of chi in the paramagnetic (PM) state indicates dominant FM interactions. The behavior of the anisotropic susceptibilities below T-N suggests a planar helical magnetic ground state with a composition-dependent pitch based on a local-moment molecular-field-theory model, with FM interactions in the ab plane and weaker AFM interactions along the helix c axis. However, the small ordered (saturation) moments similar to 0.1 mu(B) per transition metal atom, where mu(B) is the Bohr magneton, and the values of the Rhodes-Wohlfarth ratio indicate that the magnetism is itinerant. The high-field M(H) isotherms and the low-field chi(-1) (T > T-N) data were successfully analyzed within the framework of Takahashi's theory of FM spin fluctuations. The C-p (T) at low T exhibits Fermi-liquid behavior for 0 <= x <= 0.15, whereas an evolution to a logarithmic non-Fermi-liquid (NFL) behavior is found for x = 0.2 to 0.3. The logarithmic dependence is suppressed in an applied magnetic field. The low-T rho(H = 0, T) data show a T-2 dependence for 0 <= x <= 0.20 and a power-law dependence rho(H = 0, T) = rho(0) + AT(n) with n < 2 for x = 0.20 and 0.30. The exponent n shows a notable field dependence, suggesting both doping- and magnetic-field-tuned quantum critical phenomena. These low-T NFL types of behavior observed in the C-p and rho measurements are most evident near the quantum critical concentration x approximate to 0.3 at which a T = 0 composition-induced transition from the AFM phase to the PM phase occurs.

  • 2018. Melissa L. Rhodehouse (et al.). Crystal Growth & Design 18 (10), 6273-6283

    Four compounds are reported in this study. Co7Pr17 (10, cP96, P2(1)3, a = 13.4147(8) angstrom, Z = 4), either nonexistent or obscured in the Co/Pr phase diagram, has been obtained from a PrBr3 flux. With 29.2 mol % Co, it is close to Co2Pr5 (28.6 mol % Co, 2, C2Mn5 type of structure, mC28, C2/c, a = 16.5471(7) angstrom, b = 6.5107(3) angstrom, c = 7.1067(3) angstrom, beta = 96.230(3)degrees, Z = 4), existent in the Co/Pr phase diagram, produced by arc-melting of a stoichiometric mixture of the metals. The addition of the reactive metal tin to Co/Pr mixtures yielded two new ternary polar intermetallics, CoSn3Pr1-x (x = 0.04, 11, RuSn3La type, cP40, Pm(3) over barn, a = 9.587(3) angstrom, Z = 8) and Co2-xSn7Pr3 (x = 0.78, 12, Ni2-xSn7-yCe3 type, oC24, Cmmm, a = 4.5043(4) angstrom, b = 27.227(2) angstrom, c = 4.5444(3) angstrom, Z = 2). Electronic structure calculations reveal extensive heteroatomic Co-Pr interactions in the binaries with little homoatomic contributions. With tin as the third component in the ternaries, heteroatomic Co-Sn and Sn-Pr bonding interactions are dominant, following the sequence of coordination spheres around Co.

  • 2018. N. S. Sangeetha (et al.). Physical Review B 97 (1)

    Crystals of SrMn2Sb2 and BaMn2Sb2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity rho, heat capacity C-p, and magnetic susceptibility chi measurements versus temperature T, and magnetization versus field M(H) isotherm measurements. SrMn2Sb2 adopts the trigonal CaAl2Si2-type structure whereas BaMn2Sb2 crystallizes in the tetragonal ThCr2Si2-type structure. The rho(T) data indicate semiconducting behaviors for both compounds with activation energies of greater than or similar to 0.35 eV for SrMn2Sb2 and 0.16 eV for BaMn2Sb2. The chi(T) and C-p(T) data reveal antiferromagnetic (AFM) ordering at T-N = 110 K for SrMn2Sb2 and 450 K for BaMn2Sb2. The anisotropic chi(T <= T-N) data also show that the ordered moments in SrMn2Sb2 are aligned in the hexagonal ab plane whereas the ordered moments in BaMn2Sb2 are aligned collinearly along the tetragonal c axis. The ab-plane M(H) data for SrMn2Sb2 exhibit a continuous metamagnetic transition at low fields 0 < H less than or similar to 1 T, whereas BaMn2Sb2 exhibits no metamagnetic transitions up to 5.5 T. The chi(T) and C-p(T) data for SrMn2Sb2 and BaMn2Sb2 indicate strong dynamic short-range AFM correlations above their respective TN up to at least 900 K within a local-moment picture, corresponding to quasi-two-dimensional magnetic behavior. The present results and a survey of the literature for Mn pnictides with the CaAl2Si2 and ThCr2Si2 crystal structures show that the T-N values for the CaAl2Si2-type compounds are much smaller than those for the ThCr2Si2-type materials.

  • 2018. Chris Celania, Volodymyr Smetana, Anja-Verena Mudring. CrystEngComm 20 (3), 348-355

    Herein, two new tetragonal complex metallic alloys (CMAs) have been discovered and characterized: Gd2Au15-xSbx [x = 3.0-3.6; I4/mmm; tI34; a = 7.31-7.33 angstrom, c = 14.05-14.11 angstrom; V = 750.2-758 angstrom(3)] and BaAuxGa12-x [x = 3.6-4.4; I4/mcm; tI104; a = 8.77-8.78 angstrom, c = 26.06-26.13 angstrom; V = 2006.5-2010 angstrom(3)]. Both structures incorporate significant anionic site mixing and intricate positional disorder. Gd2Au15-xSbx represents a new structure type with in-plane disordered, but strongly geometrically restricted rhombi motifs. These rhombi connect through additional mixed Au/Sb positions along the c axis; this forms octahedral fragments. BaAuxGa12-x finds its place within the extended NaZn13 structural family, displaying cation-centered snub cubes with empty, distorted icosahedra (allowing for the 1 : 12 ratio) and tetrahedral stars. The split positions order due to geometric constraints to form nets of crown cyclooctane-like sheets in two different conformations. Adjacent planes adopt opposite conformations, forming layers of snub cubes with order between layers, but disorder across the greater structure. The substantial degree of mixing in both structures, together with mutual orientation of the ordered and disordered positions, suggests significant importance of heteroatomic bonding, typically found in polar intermetallic compounds.

  • 2018. Volodymyr Smetana (et al.). Journal of Materials Chemistry C 6 (6), 1353-1362

    Three series of intermetallic compounds Eu(T1, T2)(5)In (T = Cu, Ag, Au) have been investigated over their full compositional ranges. Single crystals of all compounds have been obtained by self-flux and were analyzed by single crystal X-ray diffraction revealing that the representatives fall into two structure types: CeCu6 (oP28, Pnma, a = 8.832(3)-9.121(2) angstrom, b = 5.306(2)-5.645(1) angstrom, c = 11.059(4)-11.437(3) angstrom, V = 518.3(3)-588.9(2) angstrom(3)) and YbMo2Al4 (t/14, /4/mmm, a = 7.139(2)-7.199(2) angstrom, c = 5.417(3)-5.508(1) angstrom, V = 276.1(2)-285.8(1) angstrom(3)). The structural preference was found to depend on the cation/anion size ratio, while the positional preference within the CeCu6 type structure shows an apparent correlation with the anion size. Chemical compression, hence, a change in cell volume, which occurs upon anion substitution, appears to be the main driving force for the change of magnetic ordering. While EuAg5In shows antiferromagnetic behavior at low temperatures, mixing Cu and Au within the same type of structure results in considerable changes in the magnetism. The Eu(Cu, Au)(5)In alloys with CeCu6 structure show complex magnetic behaviors and a strong magnetic field-induced spin-reorientation transition with the critical field of the transition being dependent on Cu/Au ratio. The alloys adopting the YbMo2Al4 type structure are ferromagnets exhibiting unusually high magnetic moments. The heat capacity of EuAu2.66Cu2.34In reveals a double-peak structure evolving with the magnetic field. However, low-temperature X-ray powder diffraction does not show a structural transition.

  • 2018. N. S. Sangeetha (et al.). Physical Review B 97 (14)

    The compound EuCo2-yAs2 with the tetragonal ThCr2Si2 structure is known to contain Eu+2 ions with spin S = 7/2 that order below a temperature T-N approximate to 47 K into an antiferromagnetic (AFM) proper helical structure with the ordered moments aligned in the tetragonal ab plane, perpendicular to the helix axis along the c axis, with no contribution from the Co atoms. Here we carry out a detailed investigation of the properties of single crystals. We consistently find about 5% vacancies on the Co site from energy-dispersive x-ray analysis and x-ray diffraction refinements. Enhanced ordered and effective moments of the Eu spins are found in most of our crystals. Electronic structure calculations indicate that the enhanced moments arise from polarization of the d bands, as occurs in ferromagnetic Gd metal. Electrical resistivity measurements indicate metallic behavior. The low-field in-plane magnetic susceptibilities x(ab) (T < T-N) for several crystals are reported that are fitted well by unified molecular field theory (MFT), and the Eu-Eu exchange interactions J(ij) are extracted from the fits. High-field magnetization M data for magnetic fields H parallel to ab reveal what appears to be a first-order spin-flop transition followed at higher field by a second-order metamagnetic transition of unknown origin, and then by another second-order transition to the paramagnetic (PM) state. For H parallel to c, the magnetization shows only a second-order transition from the canted AFM to the PM state, as expected. The critical fields for the AFM to PM transition are in approximate agreement with the predictions of MFT. Heat capacity C-p measurements in zero and high H are reported. Phase diagrams for H parallel to c and H parallel to ab versus T are constructed from the high-field M(H, T) and C-p(H, T) measurements. The magnetic part C-mag(T, H = 0) of C-p(T, H = 0) is extracted and is fitted rather well below T-N by MFT, although dynamic short-range AFM order is apparent in Cmag(T) up to about 70 K, where the molar entropy attains its high-T limit of R ln 8.

  • 2018. Melissa L. Rhodehouse (et al.). Inorganic Chemistry 57 (16), 9949-9961

    Although the Pt-Pr phase diagram has been explored well, recent work on rare-earth metal cluster halides with endohedral transition metal atoms has provided a new binary intermetallic that is nonexistent in the known phase diagram: The binary Pt3Pr4 (1) crystallizes in a new structure type (mP56, P21/c, a = 12.353(2) angstrom, b = 7.4837(9) angstrom, c = 17.279(2) angstrom, beta = 118.003(7)degrees, z = 8) With six crystallographically independent Pt as well as eight Pr positions. The subsequent detailed investigation has led to another previously unreported, binary phase with the Ga2Gd3 structure type, Pt2-xPr3 (2, tI80, I4/mcm, a = 11.931(9) A, c = 14.45(1) angstrom, z = 16), that is practically overlapping with the rhombohedral Pt2Pr3 existing in the phase diagram. Application of different tin containing fluxes to reproduce the newly detected phases brought about two almost iso-compositional temary compounds with Sn, Pt4Sn6Pr2.91 (3), and Pt4.Sn6Pr3 (4), as well as Pt12Sn24Pr4.84 (5). 3 is a representative of the Pt4Ge6Ce3 type (oP52, Pnma, a = 7.2863(3) A, b = 4.4909(2) angstrom, c = 35.114(2) angstrom), while 4 represents a new variant of the prolific T4E6R3 family (T = transition metal, E = main group (semOrnetal, R = rare-earth metal; Pt4Sn6Pr3: oP52, Pnma, a = 27.623(1) angstrom, b = 4.5958(2) A, c = 9.3499(5) A). Pt(12)sn(24)Prs_x (5) crystallizes as a variant of the Ni8Sn16Gd3 type (cI82, /m(-3), a = 12.274(1) A, z = 2). Electronic structure calculations provide hints on the origin of the structural changes (pseudo-polymorphism) for PtxPr3 with x = 1.97 and 2.00, respectively, and reveal that heteroatomic Pt-Pr bonding strongly dominates in both binaries while the addition of the reactive metal tin leads to dominating Pt-Sn bonding interactions in the ternaries; Pt Pt bonding interactions are strong but represent a minority in the binaries and are not present at all in the ternaries.

  • 2018. Chris Celania (et al.). Crystal Growth & Design 18 (2), 993-1001

    Twenty new ternary representatives of the Gd14Ag51 structure type have been synthesized within the R-Au-M family (R = Y, La-Nd, Sm-Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, Sn, Sb, Bi) using solid state synthesis techniques. The list of post transition metals (M) involved in the formation of this type of structure could be augmented by five new representatives. All compounds crystallize in the hexagonal space group P6/m (#175) with the unit cell ranges of a = 12.3136(2)-12.918(1) angstrom and c = 8.9967(3)-9.385(1) angstrom, and incorporate different degrees of Au/M mixing. The involvement of the post transition element in the structure varies from one to another compound both qualitatively and quantitatively. A rather significant phase width can be expected for the majority of compounds, however, not without exclusions. The distribution of the post transition metals within the structure has been analyzed via single crystal X-ray diffraction. While the positional disorder of one near-origin Au position is expectable for all compounds due to steric reasons, two specimens show an obvious deviation from the others including another Au position split along the c axis. Possible factors affecting this behavior are discussed.

  • 2018. Jude E. Namanga (et al.). ACS Applied Materials and Interfaces 10 (13), 11026-11036

    Ionic Ir(III) complexes are the most promising emitters in light emitting electrochemical cells (LECs), especially in the high energy emission range for which it is difficult to find emitters with sufficient efficiencies and lifetimes. To overcome this challenge, we introduced the concept of intramolecular pi-pi stacking of an ancillary ligand (6-phenyl-2,2'-bipyridine, pbpy) in the design of a new green-emitting iridium ionic transition metal complex with a fluoro-substituted cyclometallated ligand, 2-(4-fluorophenyOpyridinato (4Fppy). [Ir(4Fppy)(2)(pbpy)][PF6] has been synthesized and characterized and its photophysical and electrochemical properties have been studied. The complex emits green light with maxima at 561 and 556 nm under UV excitation from powder and thin film, respectively, and displays a high photoluminescence quantum yield (PLQY) of 78.5%. [Ir(4Fppy)(2)(pbpy)][PF6] based LECs driven under pulsed current conditions showed under an average current density of 100 A m(-2) (at 50% duty cycle) a maximum luminance of 1443 cd m(-2), resulting in 14.4 cd A(-1) and 7.4 lm W-1 current and power efficiencies, respectively. A remarkable long device lifetime of 214 h was observed. Reducing the average current density to 18.5 A m(-2) (at 75% duty cycle) led to an exceptional device performance of 19.3 cd A(-1) and 14.4 lm W1- for current and power efficiencies, an initial maximum luminance of 352 cd m(-2) and a lifetime of 617 h.

  • 2018. Thomas Bell (et al.).

    The three binary Tb/Er-rich transition metal compounds Tb3Pd2 (triterbium dipalladium), Er3Pd2 (trierbium dipalladium) and Er6Co5-x (hexaerbium pentacobalt) crystallize in the space groups Pbam (Pearson symbol oP20), P4/mbm (tP10) and P6(3)/m (hP22), respectively. Single crystals of Tb3Pd2 and Er6Co5-x suitable for X-ray structure analysis were obtained using rare-earth halides as a flux. Tb3Pd2 adopts its own structure type, which can be described as a superstructural derivative of the U3Si2 type, which is the type adopted by Er3Pd2. Compound Er6Co5-x belongs to the Ce6Co2-xSi3 family. All three compounds feature fused tricapped {TR6} (R = rare-earth metal and T = transition metal) trigonal prismatic heterometallic clusters. R3Pd2 is reported to crystallize in the U3Si2 type; however, our more detailed structure analysis reveals that deviations occur with heavier R elements. Similarly, Er6Co5-x was assumed to be stoichiometric Er4Co3 = Er6Co4.5. Our studies reveal that it has a single defective transition-metal site leading to the composition Er6Co4.72(2). LMTO (linear muffin-tin orbital)-based electronic structure calculations suggest the strong domination of heteroatomic bonding in all three structures.

  • 2017. Chris Celania, Volodymyr Smetana, Anja-Verena Mudring.

    Y3Au4 (triyttrium tetragold) and Y14Au51 (tetradecayttrium henpentacontagold), two binary representatives of Au-rich rare earth (R) systems crystallize with the space groups R (3) over bar and P6/m, adopting the Pu3Pd4 and Gd14Ag51 structure types, respectively (Pearson symbols hR(42) and hP(65)). Avariety of binary R-Au compounds have been reported, although only a few have been investigated thoroughly. Many reports lack information or misinterpret known compounds reported elsewhere. The Pu3Pd4 type is fairly common for group 10 elements Ni, Pd, and Pt, while Au representatives are restricted to just five examples, i.e. Ca3Au4, Pr3Au4, Nd Au-3(4), Gd3Au4, and Th3Au4. Sm6Au7 is suspected to be Sm3Au4 due to identical symmetry and close unit-cell parameters. The Pu3Pd4 structure type allows for full substitution of the position of the rare earth atom by more electronegative and smaller elements, i.e. Ti and Zr. The Gd14Ag51 type instead is more common for the group 11 metals, while rare representatives of group 12 are known. Y3Au4 can be represented as a tunnel structure with encapsulated cations and anionic chains. Though tunnels are present in Y14Au51, this structure is more complex and is best described in terms of polyhedral 'pinwheels' around the tunnel forming polyhedra along the c axis.

  • 2017. M. Di Marcantonio (et al.). Journal of Materials Chemistry C 5 (46), 12062-12068

    Light-emitting electrochemical cells (LECs) are attractive candidates for future low-cost lighting applications such as light-emitting smart tags, thanks to their simplicity, fully solution-based fabrication and flexibility. However, high brightness and efficiency in combination with satisfactory operation lifetimes need to be achieved for different emission colours bearing future device commercialization in mind. LECs emitting in the yellow-green spectral range, where the human eye is most sensitive are thereby particularly attractive. Here we present an improved hybrid LEC based on an Ir-iTMC, [Ir(4-Fppy)(2)(pbpy)][PF6] (4-Fppy = 2-(4-fluorophenyl) pyridinato, pbpy = 6-phenyl-2,2'-bipyridine) emitting at 557 nm. It features a luminance of 2400 cd m(-2) when driven at a constant voltage of 4 V, and a lifetime of 271 h at a luminance of 1500 cd m(-2) under pulsed current operation. The hybrid LEC shows an enhanced performance compared to a LEC solely based on the Ir-ITMC where operation lifetimes of 165 h at a luminance above 1200 cd m(-2) under pulsed current operation conditions were observed. The performance improvement was achieved by addition of a solution-processed ZnO nanoparticle film on top.

  • 2017. Min Li (et al.). Inorganic Chemistry 56 (18), 11104-11112

    Two borophosphates, (NH4)(1-2x)M1+x(H2O)(2)(BP2O8)center dot yH(2)O with M = Mn (I) and Co (II), synthesized hydrothermally crystallize in enantiomorphous space groups P6(5)22 and P6(1)22 with a = 9.6559(3) and 9.501(3) angstrom, c = 15.7939(6) and 15.582(4) angstrom, and V = 1275.3(1) and 1218.2(8) angstrom(3) for I and II, respectively. Both compounds feature helical chains composed of vertex-sharing tetrahedral PO4 and BO4 groups that are connected through O atoms to transition-metal cations, Mn2+ and Co2+, respectively. For the two crystallographically distinct-transition-metal cation sites present in the structure, this results in octahedral coordination with different degrees of distortion from the ideal symmetry. The crystal-field parameters, calculated from the corresponding absorption spectra, indicate that Mn2+ and Co2+ ions are located in a weak octahedral-like crystal field and suggest that the Co-ligand interactions are more covalent than the Mn-ligand ones. Luminescence measurements at room temperature reveal an orange emission that red-shifts upon lowering of the temperature to 77 K for I, while II is not luminescent. The luminescence lifetimes of I are 33.4 mu s at room temperature and 1.87 ms at 77 K. Both compounds are Curie-Weiss paramagnets with negative Weiss constants and effective magnetic moments expected for noninteracting Mn2+ and Co2+ cations but no clear long-range magnetic order above 2 K.

  • 2019. Alessia Provino (et al.). Inorganic Chemistry 58 (22), 15045-15059

    We investigated the U-Ni-B and Nb-Ni-B systems to search for possible new heavy fermion compounds and superconducting materials. The formation, crystal chemistry, and physical properties of U2Ni21B6 and Nb3-yNi20+yB6 [ternary derivatives of the cubic Cr23C6-type (cF116, Fm3m)] have been studied; the formation of the hypothetical U3Ni20B6 and Nb2Ni21B6 has been disproved. U2Ni21B6 [a = 10.6701(2) angstrom] crystallizes in the ordered W2Cr21C6-type, whereas Nb3-yNi20+yB6 [a = 10.5842(1) angstrom] adopts the Mg3Ni20B6-type. Ni in U2Ni21B6 can be substituted by U, leading to the solid solution U2-xNi21+yB6 (0 <= x <= 0.3); oppositely, Nb in Nb3Ni20B6 is partially replaced by Ni, forming the solution Nb3-yNi20+yB6 (0 <= y <= 0.5), none of them reaching the limit corresponding to the hypothetically ordered U3Ni20B6 and Nb2Ni21B6. These results prompted us to investigate quaternary compounds U2-zNbzNi21B6 and U6Nb3-delta Ni20B6: strong competition in the occupancy of the 4a and 8c sites by U, Nb, and Ni atoms has been observed, with the 4a site occupied by U/Ni atoms only and the 8c site filled by U/Nb atoms only. U2Ni21B6, U2.3Ni20.7B6, and Nb3Ni20B6 are Pauli paramagnets. Interestingly, Nb2.5Ni20.5B6 shows ferromagnetism with T-c approximate to 11 K; the Curie-Weiss fit gives an effective magnetic moment of 2.78 mu(B)/Ni, suggesting that all Ni atoms in the formula unit contribute to the total magnetic moment. The M(H) data at 2 K further corroborate the ferromagnetic behavior with a saturation moment of 10 mu(B)/fu (approximate to 0.49 mu(B)/Ni). The magnetic moment of Ni at the 4a site induces a moment in all of the Ni atoms of the whole unit cell (32f and 48h sites), with all atoms ordering ferromagnetically at 11 K. Density functional theory (DFT) shows that the formation of U2Ni21B6 and Nb3Ni20B6 is energetically preferred. The various electronic states generating ferromagnetism on Nb2.5Ni20.5B6 and Pauli paramagnetism on U2Ni21B6 and Nb3Ni20B6 have been identified.

  • 2020. Volodymyr Smetana (et al.). Inorganic Chemistry 59 (1), 818-828

    A series of anhydrous acetate salts with uranium {[C(2)C(1)im][UO2(OAc)(3)] (1), [C(2)C(2)im][UO2(OAc)(3)] (2), and [C(4)C(1)im][UO2(OAc)(3)] (3)}, lanthanides {[C(2)C(2)im](2) [La(OAc)(5)] (4) and [C(2)C(1)im](2) [Nd(OAc)(5)] (5)}, and strontium {[C(2)C(1)im](n)[Sr-(OAc)(3)](n) (6)} (where C(2)C(1)im = 1-ethyl-3-methylimidazolium, C2C2 im = 1,3-diethylimidazolium, C4C1 im = 1-butyl-3-methylimidazolium, and OAc = acetate) have been prepared and structurally characterized. Both lanthanides and strontium are common components of the nuclear fuel waste, and their separation from uranium is an important but still challenging task. A new synthetic approach with dialkylimidazolium acetate ionic liquids (ILs) as the solvent has been developed for the direct synthesis of homoleptic acetates from the corresponding hydrates and, unexpectedly, hardly soluble f-element oxides. Although the group of characterized compounds shows perfect structural variability, all actinide and lanthanide metal ions form monomeric complex anions where the metal cation coordinates to five ligands including two oxygen atoms in the case of uranium, as is commonly observed for uranyl compounds. Crystallographic analyses revealed that the complex [UO2(OAc)(3)](-) anions possess rather standard D-3h symmetry featuring a hexagonal-bipyramidal coordination environment, while the lanthanide anions [Ln(OAc)(5)](2-) are fully asymmetric and the Ln(3+) cations are 10-coordinated in the form of a distorted bicapped tetragonal antiprism. This is the first report of lanthanide ions coordinated in this fashion. For Sr2+, 9-fold coordination through oxygen atoms in the form of a strongly distorted tricapped trigonal prism is observed. The crystallization of anhydrous, homoleptic, anionic acetate complexes from such a large variety of different metal salts appears to be due to the properties of dialkylimidazolium acetate ILs themselves, including enhanced basicity from the high concentration of free anions and their greater affinity for hydrogen-bonding solutes relative to metal cations.

  • 2020. Steven P. Kelley (et al.). Crystal Growth & Design 20 (1), 498-505

    The reaction of 1,3-dimethylimidazolium-2-carboxylate with elemental iodine in acetonitrile rapidly affords crystalline iodide salts of the 1,3-dimethy1-2-iodoimidazolium cation ([C(1)mim-2-I](+)), [C(1)mim-2-I]I.0.5I(2), and [C(1)mim-2-1]I-0.5CH(3)CN, depending on the temperature. Analysis of the two structures shows the significant role of halogen bonding interactions between the cation and anion in the [C(1)mim-2-I]I salts, which reduces the ionicity of the compounds. This observation is backed by theoretical calculations revealing the importance of halogen bonding as a design strategy for ionic liquids (ILs), which, so far, has been underestimated. The halogen bonding is also analyzed in terms of this new design concept for ILs.

  • 2020. Olivier Renier (et al.). Crystal Growth & Design 20 (1), 214-225

    Ionic liquids present a versatile, highly tunable class of soft functional materials. Aside from being low melting salts, they can be endowed with additional functionalities. In N-alkylimidazolium halides, which are a prominent class of ionic liquids (ILs), the imidazolium cation was linked via an ether-bridge to an azobenzene unit in order to obtain photoresponsive materials through photoinduced trans-cis isomerization. The azobenzene unit, in turn, was modified with electron-donating or -withdrawing groups such as methyl-, tert-butyl-, methoxy-, N,N-dimethylamino, and nitro groups to study their influence on the photoisomerization and phase behavior. Endowing the imidazolium additionally with a long alkyl chain allows the materials to potentially form liquid crystalline (LC) mesophases before melting into the isotropic liquid. All studied compounds qualify as ionic liquids, and all, except for the nitro-compound, show the formation of smectic mesophases melting to the isotropic liquid. The compounds with the bulkiest aliphatic substituent, the tert-butyl, shows the lowest melting point, the largest mesophase window, and an efficient photochemical trans-cis conversion (>90%). In summary, by tuning sterically and electronically the cationic part of ILs, a photoswitchable room temperature liquid crystal could be developed and design guidelines for photoresponsive ionic liquids could be obtained.

  • 2020. Volodymyr Babizhetskyy (et al.). Zeitschrift für Naturforschung. B, A journal of chemical sciences 75 (1-2), 135-142

    Two new quaternary selenides of the alpha-TlSe structure type have been synthesized and characterized. Single crystal X-ray diffraction analysis has revealed that Tl2Ga2SnSe6 crystallizes with space group I4/mmc, a =8.095(1), c=6.402(1) angstrom, with a refined composition of Tl1-xGa1-ySny Se-2 (x= y=0.345(5)), Z=4, R1=0.028; wR2= 0.066. The crystal structure of the isostructural compound Tl2Ga2GeSe6 has been determined by means of powder X-ray diffraction: space group I4/mmc, Z= 4, a= 8.0770(4 ), c= 6.2572(5) angstrom, refined composition Tl1-xGa1-ySny Se-2, x=0343(5), y=0.35(2), (R-B(I) = 0.084; R-p = 0.041; R-PW= 0.058). According to their optical absorption spectra all compounds are semiconductors with relatively narrow direct band gaps of 2.15(3) and 2.05(5) eV for the Ge and Sn phase, respectively.

  • 2020. F. Guillou (et al.). Journal of Magnetism and Magnetic Materials 501

    Rare-earth anti-perovskites with oxygen are an interesting magnetic materials family at the boundary between intermetallics and oxides, they however remain largely unexplored. Here, magnetic and heat capacity investigations, as well as density functional theory (DFT) calculations, were carried out on SnOEu3. At low magnetic field (B <= 0.5 T), a Neel temperature separates antiferromagnetic and paramagnetic phases at 31 K. When applying higher magnetic field below the Neel temperature, successive transformations toward a ferromagnetic state via a number of intermediate canted magnetic structures are observed and are associated with only modest latent heat and transition entropy. High-pressure magnetic measurements confirm the stable divalent state of Eu up to 1.05 GPa. A direct magnetocaloric effect progressively increases with applied magnetic field above the Neel temperature, reaching -16 J kg(-1) K-1 for Delta B = 7 T. On the other hand, the inverse magnetocaloric effect of the field-induced transition below T-N saturates at similar to+ 5 J kg(-1) K-1. DFT calculations support magnetic instabilities observed experimentally in SnOEu 3 and reveal an unusual exchange mechanism and band topology near the Fermi level.

  • 2020. Steven P. Kelley (et al.). Inorganic Chemistry 59 (5), 2861-2869

    We investigated whether the relatively Lewis basic imidazole-2-thiones could be used to substitute water ligands bound to f-element cations and generate f-element soft donor complexes. Reactions of 1,3-diethylimidazole-2-thione (C(2)C(2)ImT) with Nd(NO3)(3)center dot 6H(2)O and UO2Cl2 center dot 3H(2)O led to the isolation of the anhydrous thione complexes Nd(NO3)(3)(C(2)C(2)ImT)(3) and UO2Cl2(C(2)C(2)ImT)(2), characterized by single crystal X-ray diffraction. Differences in the strength of metal-thione interactions have been examined by means of the crystal structure analysis and density functional theory (DFT) calculations. The C(2)C(2)ImT ligands were found to be affected by both coordination and noncovalent interactions, making it impossible to deconvolute the effects of one from the other. Calculated partial atomic charges indicated greater ligand-to-metal charge transfer in the [UO2](2+) complex, indicative of a stronger interaction. The reactivity of C(2)C(2)ImT demonstrates its usefulness in the preparation of f-element soft donor complexes from readily available hydrates that could be useful intermediates for promoting the coordination and studying the effects of soft donor anions.

  • 2020. Steven P. Kelley (et al.). Chemical Communications 56 (30), 4232-4235

    By dehydrating actinide salts with an ionic liquid containing a common anion and subsequent reaction with N-heterocyclic ligands, we challenge the concept that actinides prefer O- over N-donors; rather the acidic hydrogen atoms of protic solvents hinder the formation of more elusive f-element N-donor coordination complexes.

Show all publications by Volodymyr Smetana at Stockholm University

Last updated: June 11, 2020

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