Browsing by Author "Graubner, Tim"

Now showing 1 - 13 of 13
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    [Br4F21]− - a unique molecular tetrahedral interhalogen ion containing a μ4-bridging fluorine atom surrounded by BrF5 molecules
    (Royal Society of Chemistry, 2024-03-07) Möbs, Martin; Graubner, Tim; Karttunen, Antti J.; Kraus, Florian; Department of Chemistry and Materials Science; Inorganic Materials Modelling; University of Marburg
    The reaction of [NMe4][BrF6] with an excess of BrF5 leads to the compound [NMe4][Br4F21]·BrF5. It features molecular [(μ4-F)(BrF5)4]− anions of tetrahedron-like shape containing central μ4-bridging F atoms coordinated by four BrF5 molecules. It is the most BrF5-rich fluoridobromate anion by mass. Quantum-chemical calculations showed that the μ4-F-Br bonds within the anion are essentially ionic in nature. The compound is the first example where F atoms bridge μ4-like neither to metal nor to hydrogen atoms. It was characterized by Raman spectroscopy and by single-crystal X-ray diffraction. The latter showed surprisingly that its crystal structure is related to the intermetallic half-Heusler compound and structure type MgAgAs.
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    Bromine Pentafluoride BrF5, the Formation of [BrF6]− Salts, and the Stereochemical (In)activity of the Bromine Lone Pairs
    (WILEY-VCH VERLAG, 2022-12-27) Möbs, Martin; Graubner, Tim; Eklund, Kim; Karttunen, Antti J.; Kraus, Florian; Department of Chemistry and Materials Science; Inorganic Materials Modelling; University of Marburg
    BrF5 can be prepared by treating BrF3 with fluorine under UV light in the region of 300 to 400 nm at room temperature. It was analyzed by UV-Vis, NMR, IR and Raman spectroscopy. Its crystal structure was redetermined by X-ray diffraction, and its space group was corrected to Pnma. Quantum-chemical calculations were performed for the band assignment of the vibrational spectra. A monoclinic polymorph of BrF5 was quantum chemically predicted and then observed as its low-temperature modification in space group P21/c by single crystal X-ray diffraction. BrF5 reacts with the alkali metal fluorides AF (A=K, Rb) to form alkali metal hexafluoridobromates(V), A[BrF6] the crystal structures of which have been determined. Both compounds crystallize in the K[AsF6] structure type (R (Formula presented.), no. 148, hR24). For the species [BrF6]+, BrF5, [BrF6]−, and [IF6]−, the chemical bonds and lone pairs on the heavy atoms were investigated by means of intrinsic bond orbital analysis.
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    A Computational Study on Closed-Shell Molecular Hexafluorides MF6 (M=S, Se, Te, Po, Xe, Rn, Cr, Mo, W, U) – Molecular Structure, Anharmonic Frequency Calculations, and Prediction of the NdF6 Molecule
    (WILEY-VCH VERLAG, 2023-05-02) Graubner, Tim; Karttunen, Antti J.; Kraus, Florian; University of Marburg; Department of Chemistry and Materials Science
    Quantum chemical methods were used to study the molecular structure and anharmonic IR spectra of the experimentally known closed-shell molecular hexafluorides MF6 (M=S, Se, Te, Xe, Mo, W, U). First, the molecular structures and harmonic frequencies were investigated using Density Functional Theory (DFT) with all-electron basis sets and explicitly considering the influence of spin-orbit coupling. Second, anharmonic frequencies and IR intensities were calculated with the CCSD(T) coupled cluster method and compared, where available, with IR spectra recorded by us. These comparisons showed satisfactory results. The anharmonic IR spectra provide means for identifying experimentally too little studied or unknown MF6 molecules with M=Cr, Po, Rn. To the best of our knowledge, we predict the NdF6 molecule for the first time and show it to be a true local minimum on the potential energy surface. We used intrinsic bond orbital (IBO) analyses to characterize the bonding situation in comparison with the UF6 molecule.
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    A Dinuclear Uranium Complex [{UO2F2(NH3)}2(μ-F)2]2− from Reaction of TlF and UO2F2 in Liquid Anhydrous Ammonia and Fluoride Ion Affinities for Some Uranyl(VI) Species [UO2Fx]2−x and [UO2Fx(NH3)5−x]2−x
    (Wiley-VCH Verlag, 2023-10-02) Graubner, Tim; Karttunen, Antti J.; Kraus, Florian; Department of Chemistry and Materials Science; Inorganic Materials Modelling; University of Marburg
    UO2F2 abstracts F− anions from TlF in liquid ammonia solution and the compound [Tl2(NH3)6][{UO2F2(NH3)}2(μ-F)2] is formed. The compound has been characterized by single crystal X-ray diffraction, Raman spectroscopy and quantum-chemical calculations for the solid state. Quantum-chemical investigation of the [{UO2F2(NH3)}2(μ-F)2]2− anion showed that the U−(μ-F)−U σ-3c-4e-bond is essentially ionic. The [Tl2(NH3)6]2+ cation shows a thallophilic Tl⋅⋅⋅Tl interaction. Fluoride ion affinities (FIAs) were calculated for different UO22+ species [UO2Fx]2−x and [UO2Fx(NH3)5−x]2−x with x=0 to 4.
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    A Fresh Look at a Well-Known Solid: Structure, Vibrational Spectra, and Formation Energy of NaNH2
    (American Chemical Society, 2023-06-29) Bonometti, Laura; Kraus, Florian; Graubner, Tim; Karttunen, Antti J.; Civalleri, Bartolomeo; Donà, Lorenzo; Maschio, Lorenzo; University of Turin; University of Marburg; Department of Chemistry and Materials Science; Department of Chemistry and Materials Science
    Sodium amide (NaNH2) in its α form is a common compound that has recently seen renewed interest, mainly for its potential use as a solid-state hydrogen storage material. In this work, we present a synergic theoretical and experimental characterization of the compound, including novel measured and simulated vibrational spectra (IR and Raman) and X-ray diffraction patterns. We put forward the hypothesis of a low-temperature symmetry breaking of the structure to space group C2/c, while space group Fddd is commonly reported in the literature and experimentally found down to 80 K. Additionally, we report a theoretical estimate of the heat of formation of sodium amide from ammonia to be equal to -12.2 kcal/mol at ambient conditions.
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    Reactions in Anhydrous Liquid Ammonia : Syntheses and Crystal Structures of [M(NH3)8]I2 (M = Eu, Yb) with Bicapped Trigonal-Prismatic Octaammine Lanthanoid(II) Cations
    (WILEY-V C H VERLAG GMBH, 2020-08-31) Rudel, Stefan S.; Graubner, Tim; Karttunen, Antti J.; Kraus, Florian; University of Marburg; Department of Chemistry and Materials Science
    The compounds [M(NH3)8]I2 (M = Eu, Yb) were obtained from reactions in anhydrous liquid ammonia solutions as side products. They were characterized by single-crystal X-ray diffraction and found to be isotypic to the compounds [Ca(NH3)8]X2 (X = Cl, Br, I). The coordination sphere of the lanthanoid(II) cations is not square-antiprismatic but much better described as bicapped trigonal-prismatic. In contrast, quantum-chemical gas-phase calculations show the square-antiprismatic coordination polyhedron (point group S8) to be energetically favored over the bicapped trigonal prism and the latter is not even a true local minimum. Obviously, hydrogen bonding and eventually other weak interactions have an impact on the observed bicapped trigonal-prismatic coordination sphere of the [M(NH3)8]2+ cations in the solid state.
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    Reactions of [SiF4(NH3)2] with Fluorides AF (A = Li-Cs, Tl, NH4) in Liquid NH3: A [NH4(NH3)2]+ Cation and a Thallophilic Interaction in [Tl2(NH3)6]2+
    (AMERICAN CHEMICAL SOCIETY, 2021-10-04) Rudel, Stefan S.; Graubner, Tim; Karttunen, Antti J.; Dehnen, Stefanie; Kraus, Florian; University of Marburg; Department of Chemistry and Materials Science
    We investigated whether [SiF4(NH3)2] can act as a fluoride-ion acceptor in its reactions with the fluorides AF (A = Li-Cs, Tl, NH4) in anhydrous liquid ammonia (NH3). While LiF and NaF did not react, we obtained the compounds K[SiF5(NH3)], Rb[SiF5(NH3)], and Cs[SiF5(NH3)], as well as [NH4(NH3)2]2[SiF6] and [Tl2(NH3)6][SiF6]·2NH3, from the other starting materials and characterized them by either single-crystal or powder X-ray diffraction. The compound [NH4(NH3)2]2[SiF6] contains the very rarely observed hydrogen-bonded, C2v-symmetric diammine ammonium cation [NH4(NH3)2]+, and the compound [Tl2(NH3)6][SiF6]·2NH3 is an example for an uncommon Tl(I)-Tl(I) interaction. This "thallophilic" interaction was investigated with quantum-chemical methods.
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    Reactions of ThX4 (X=F, Cl, Br, I) with Liquid Ammonia-Crystal Structures and a Theoretical Study of Ammine Thorium(IV) Halide Ammoniates
    (WILEY-VCH VERLAG, 2021-07-22) Deubner, H. Lars; Graubner, Tim; Weigend, Florian; Karttunen, Antti J.; Kraus, Florian; Department of Chemistry and Materials Science; Inorganic Materials Modelling; University of Marburg
    Reactions of thorium tetrahalides ThX4 (X=Cl, Br, I) with liquid ammonia at room temperature lead to the formation of decaammine thorium(IV) halide ammoniates. Their different compositions [Th(NH3)10]X4 ⋅ nNH3 were established by single crystal X-ray diffraction. While for the chloride the formation of a tetraammoniate is observed, the reaction of the bromide leads to an octaammoniate, whereas the iodide results in approximately a nonaammoniate. Additionally, the formation of the dinuclear Th complex compound [Th2Cl2(NH3)14(μ-O)]Cl4 ⋅ 3NH3 was observed when moisture was present within NH3. As expected, the Th and the previously reported U compounds [An(NH3)10]Br4 ⋅ 8NH3 (Pbca, An=Th, U), [An(NH3)10]I4 ⋅ 9NH3 (P4/n), and [An2Cl2(NH3)14(μ-O)]Cl4 ⋅ 3NH3 (P (Formula presented.)) are isotypic, respectively. Surprisingly, ThCl4 formed the decaammine complex [Th(NH3)10]Cl4 ⋅ 4NH3 (P121/n1), while UCl4 formed the octaammine chlorido complex [UCl(NH3)8]Cl3 ⋅ 3NH3 (Pnma) in ammonia. Quantum-chemical gas-phase calculations were carried out to study the molecular structures and the energetics of the complex cations. In addition, the localized molecular orbitals (LMO) and Intrinsic Bonding Orbitals (IBO) were analyzed. However, the calculations could not explain the preferred formation of the [Th(NH3)10]4+ complex over the hypothetical cation [ThCl(NH3)8]3+.
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    Surprises in the Solvent-Induced Self-Ionization in the Uranium Tetrahalide UX4(X = Cl, Br, I)/Ethyl Acetate System
    (AMERICAN CHEMICAL SOCIETY, 2022-04-12) Deubner, H. Lars; Graubner, Tim; Buchner, Magnus R.; Weigend, Florian; Ivlev, Sergei I.; Karttunen, Antti J.; Kraus, Florian; Department of Chemistry and Materials Science; Inorganic Materials Modelling; University of Marburg
    The reaction of the uranium(IV) halides UCl4, UBr4, or UI4 with ethyl acetate (EtOAc) leads to the formation of the complexes [UX3(EtOAc)4][UX5(EtOAc)] (X = Cl, Br) or [UI4(EtOAc)3]. Thus, both UCl4 and UBr4 show self-ionization in ethyl acetate to a distorted pentagonal bipyramidal [UX3(EtOAc)4]+ cation and a distorted octahedral [UX5(EtOAc)]- anion. Surprisingly, the chloride and bromide compounds are not isotypic. While [UCl3(EtOAc)4][UCl5(EtOAc)] crystallizes in the orthorhombic crystal system, space group P212121 at 250 K, the bromide compound crystallizes in the monoclinic crystal system, P121/n1 at 100 K. Unexpectedly, UI4 does not show self-ionization but forms [UI4(EtOAc)3] molecules, which crystallize in the monoclinic crystal system, P21/c, at 100 K. The compounds were characterized by single-crystal X-ray diffraction, IR, Raman, and NMR spectroscopy, as well as molecular quantum chemical calculations using solvent models.
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    A Symmetric F−H−F Hydrogen Bond in Strontium Bifluoride, Sr[HF2]2
    (WILEY-V C H VERLAG GMBH, 2022-05-25) Stene, Riane E.; Graubner, Tim; Ivlev, Sergei I.; Karttunen, Antti J.; Kraus, Florian; University of Marburg; Department of Chemistry and Materials Science
    Single crystal X-ray diffraction shows the hydrogen bond within the [F−H−F]− anion of Sr[HF2]2 to be symmetric with H−F bond lengths of 1.143(5) Å and an intramolecular F⋅⋅⋅F distance of 2.2826(18) Å. The [HF2]− anion adopts crystallographic C2-symmetry, however, it is essentially linear with a F−H−F angle of 174(4)°. Solid-state quantum chemical calculations agree with the experimental findings, showing a slightly bent F−H−F angle of 177.8°. The decomposition of Sr[HF2]2 to SrF2 and HF is endothermic by +64 kJ/mol at room temperature. The bonding in the [F−H−F]− anion is clearly ionic both in the solid state and gas phase.
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    Uranium Chemistry in liquid Ammonia: Compounds obtained by adventitious Presence of Moisture or Air
    (Wiley-VCH Verlag, 2024-05-13) Graubner, Tim; Woidy, Patrick; Baer, Sebastian A.; Karttunen, Antti J.; Kraus, Florian; Department of Chemistry and Materials Science; Inorganic Materials Modelling; University of Marburg
    UCl4, UBr4, UBr5, or UO2Cl2 reacted with excess liquid ammonia – in adventitious presence of moisture and/or air – and formed some peculiar uranium compounds of which we present the crystal structures. [(NH3)7(N3)U(μ-O)U(NH3)8]Cl5 ⋅ 7NH3 contains a dinuclear μ-O-bridged uranium(IV) cation, [{(NH3)4UO2}2(μ-O)]Cl2 ⋅ 4NH3 features a dinuclear μ-O-bridged uranyl(VI) cation, while the compounds [(U(VI)O2)2(U(V)O2)2(μ3-O)2(NH3)12]Br2 ⋅ 6NH3 and [(U(VI)O2)4(U(V)O2)4(μ3-O)4(NH3)22]Br4 ⋅ 16NH3 are mixed-valent containing uranyl(V)-uranyl(VI) units. For these tetra- and octanuclear complex cations we observed that the O atoms of the uranyl(V) units can be μ2- and even μ3-bridging to uranyl(VI) units, while the O atoms of the latter are acting as terminal ligands only. [(NH3)8U(μ-N)U(NH3)5(μ-N)UO2(NH3)4]Br6 ⋅ 18NH3 presents the first example of a compound where the isoelectronic species UO22+ and UN2 formed a complex with the NUN unit bridging to the U atom of the uranyl(VI) cation. As it is can be difficult to distinguish between N and O atoms with X-ray diffraction, quantum-chemical calculations at the DFT-PBE0/TZVP level of theory were carried out which unequivocally confirmed the atom assignments in the crystal structures. The chemical bonding in the complex cations was studied using intrinsic bonding orbitals and allowed for an additional discrimination of the U(V) and U(VI) atoms in the mixed-valent compounds.
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    Uranium Cyanides from Reactions in Liquid Ammonia Solution
    (Wiley-VCH Verlag, 2024-06-03) Graubner, Tim; Rudel, Stefan S.; Ivlev, Sergei I.; Karttunen, Antti J.; Kraus, Florian; Department of Chemistry and Materials Science; Inorganic Materials Modelling; University of Marburg
    Reactions of uranium tri- and tetrahalides, UBr3, UI3, UCl4, and UI4, with different cyanides MCN (M=K, Ag) in liquid anhydrous ammonia led to three novel uranium(IV) cyanide compounds. The reaction of UCl4 in the presence of KCN resulted in the compound [U(CN)(NH3)8]Cl3 ⋅ 3NH3, while UBr3 and UI3 were oxidized in the presence of AgCN to form the compounds (Formula presented.) (μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]Br4 ⋅ 2NH3, and (Formula presented.) (μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]I4 ⋅ 2NH3. The reaction of UI4 with KCN in aNH3 also yielded the compound (Formula presented.) (μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]I4 ⋅ 2NH3. The compounds (Formula presented.) (μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]X4 ⋅ 2NH3 (X=Br, I) crystallize in different space groups, Pmn21 (no. 31) and Imm2 (no. 44), respectively. In both cases, the (Formula presented.) (μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]4+ cation forms infinite strands. We conducted quantum-chemical calculations and Intrinsic Bond Orbital analyses on the observed [U(CN)(NH3)8]3+ cation and the [(μ-CN)2{(H3N)5U(μ-NH2)3U(NH3)5}]3+ model cation to gain insight into the bonding situation.
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    [(μ3-F)(BrF5)3]− – An Unprecedented Molecular Fluoridobromate(V) Anion in Cs[Br3F16]
    (Wiley-VCH Verlag, 2023-09-01) Möbs, Martin; Graubner, Tim; Karttunen, Antti J.; Kraus, Florian; University of Marburg; Department of Chemistry and Materials Science
    The reaction of Cs[BrF6] with BrF5 gave the compound Cs[Br3F16] with the unprecedented propeller-shaped, C3-symmetric [(μ3-F)(BrF5)3]− anion. All other currently known fluoridobromates(V) contain only octahedral [BrF6]− anions, which, unlike the related [IF6]− anions, never exhibited stereochemical activity of the lone pair on the Br atoms. Despite the same coordination number of six for the Br atom in the [BrF6]− and [(μ3-F)(BrF5)3]− anions, the longer μ3-F−Br bonds provide additional space, allowing the lone pairs on the Br atoms to become stereochemically active. Cs[Br3F16] was characterized by single-crystal X-ray diffraction, Raman spectroscopy, and quantum-chemical calculations for both the solid-state compound and the isolated anion at 0 K. Intrinsic bond orbital calculations show that the μ3-F−Br bond is essentially ionic in nature and also underpin the stereochemical activity of the lone pairs of the Br(V) atoms.