Elusive Zintl Ions [µ HSi4]3− and [Si5]2− in Liquid Ammonia: Protonation States, Sites, and Bonding Situation by NMR and Theory

F. Hastreiter, C. Lorenz, J. Hioe, S. Gärtner, L. Nanjundappa, N. Korber, R.M. Gschwind, Angew. Chem. Int. Ed., 2019, 58, 3133-3137.

The existence of [μ-HSi₄]³⁻ in liquid ammonia solutions is confirmed by ¹H and ²⁹Si-NMR experiments. Both NMR and quantum chemical calculations reveal that the H atom bridges two Si atoms of the [Si₄]⁴⁻ cluster, contrary to the expectation that it is located at one vertex Si of the tetrahedron. The calculations also indicate that in the formation of [μ-HSi₄]³⁻, protonation is driven by a high charge density and an increase of electron delocalization compared to [Si₄]⁴⁻. Additionally, [Si₅]²⁻ was detected for the first time and characterized by NMR. Calculations show that it is resistant to protonation, owing to a strong charge delocalization, which is significantly reduced upon protonation. Thus, our methods reveal three silicides in liquid ammonia: unprotonated [Si₅]²⁻, terminally protonated [HSi₉]³⁻, and bridge?protonated [μ-HSi₄]³⁻. The protonation trend can be roughly predicted by the difference in charge delocalization between the parent compound and the product, which can be finely tuned by the presence of counter ions in solution.

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[Co@Sn6 Sb6 ]3− : An Off-Center Endohedral 12-Vertex Cluster

R.J. Wilson, F. Hastreiter, K. Reiter, P. Büschelberger, R. Wolf, R.M. Gschwind, F. Weigend, S. Dehnen, Angew. Chem. Int. Ed., 2018, 57, 15359-15363.

We report on the asymmetric occupation of a 12-vertex cluster centered by a single metal atom. Three salts of related intermetalloid cluster anions, [Co@Sn₆Sb₆]³⁻ (1), [Co₂@Sn₅Sb₇]³⁻ (2), and [Ni₂@Sn₇Sb₅]³⁻ (3) were synthesized, which have pseudo?C_4v-symmetric or pseudo-D_4h-symmetric 12-vertex Sn/Sb shells and interstitial Co⁻ ions or Ni atoms. Anion 1 is a very unusual single?metal?“centered” 12?atom cluster, with the inner atom being clearly offset from the cluster center for energetic reasons. Quantum chemistry served to assign atom types to the atomic positions and relative stabilities of this cluster type. The studies indicate that the structures are strictly controlled by the total valence electron count—which is particularly variable in ternary intermetalloid cluster anions. Preliminary ¹¹⁹Sn NMR studies in solution, supported by quantum?chemical calculations of the shifts, illustrate the complexity regarding Sn:Sb distributions of such ternary systems.

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The Structure of [HSi9]3− in the Solid State and Its Unexpected Highly Dynamic Behavior in Solution

C. Lorenz, F. Hastreiter, J. Hioe, L. Nanjundappa, S. Gärtner, N. Korber, R.M. Gschwind, Angew. Chem. Int. Ed., 2018, 57, 12956-12960.

We report on the first unambiguous detection of the elusive [HSi₉]³⁻ anion in solutions of liquid ammonia by various ²⁹Si and ¹H?NMR experiments including chemical exchange saturation transfer (CEST). The characteristic multiplicity patterns of both the ²⁹Si and ¹H resonances together with CEST and a partially reduced ¹H,²⁹Si coupling constant indicate the presence of a highly dynamic Si₈ entity and a Si−H moiety with slow proton hopping. Theoretical calculations corroborate both reorganization of Si₈ on the picosecond timescale via low vibrational modes and proton hopping. In addition, in a single-crystal X-ray study of (K(DB[18]crown-6))(K([2.2.2]crypt))₂[HSi₉]⋅8.5 NH₃, the H?atom was unequivocally localized at one vertex of the basal square of the monocapped square antiprismatic cluster. Thus experimental studies and theoretical considerations provide unprecedented insight into both the structure and the dynamic behavior of these cluster anions, which hitherto had been considered to be rigid.

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Stability and Conversion of Tin Zintl Anions in Liquid Ammonia Investigated by NMR Spectroscopy

F. Fendt , C. Koch , M. Neumeier , S. Gärtner, R. M. Gschwind, N. Korber, Chem. Eur. J., 2015, 21, 14539-14544.

Homoatomic polyanions of post-transition main?group metals, namely, Zintl anions, are precast in analogous Zintl phases and can react in solution to form new materials. Despite comprehensible reaction approaches, the formed products cannot be planned in advance, as hitherto undetected and therefore disregarded side reactions take place. The outcomes and interpretations of the reactions of Zintl anions are so far based mainly on crystal structures, which only allow characterization of the product that has the lowest solubility. Here we present the results of our investigation of the stability of highly charged tin Zintl anions in liquid ammonia, which is not exclusively based on solution effects but also on the oxidative influence of the solvent. This allows for a deeper understanding of the ongoing processes in solution and opens doors to the directed synthesis of transition metal complexes of Sn₄⁴⁻, here shown by its reactivity towards MesCu.

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A Nano-sized Supramolecule Beyond the Fullerene Topology

F. Dielmann, C. Heindl, F. Hastreiter, E. V. Peresypkina, A. V. Virovets, R. M. Gschwind, M. Scheer, Angew. Chem. Int. Ed., 2014, 53, 13605-13608.

The reaction of [Cp^BnFe(η⁵?P₅)] (1) (Cp^Bn=η⁵?C₅(CH₂Ph)₅) with CuI selectively yields a novel spherical supramolecule (CH₂Cl₂)_3.4@[(Cp^BnFeP₅)₁₂{CuI}₅₄(MeCN)_1.46] (2) showing a linkage of the scaffold atoms which is beyond the Fullerene topology. Its extended CuI framework reveals an outer diameter of 3.7-nm—a size that has not been reached before using five-fold symmetric building blocks. Furthermore, 2 shows a remarkable solubility in CH₂Cl₂, and NMR spectroscopy reveals that the scaffold of the supramolecule remains intact in solution. In addition, a novel 2D polymer [{Cp^BnFe(η⁵?P₅)}₂{Cu₆(μ?I)₂(μ₃?I)₄}]_n (3) with an uncommon structural motif was isolated. Its formation can be avoided by using a large excess of CuI in the reaction with 1.

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Stabilization of Tetrahedral P₄ and As₄ Molecules as Guests in Polymeric and Spherical Environments

C. Schwarzmaier, A. Schindler, C. Heindl, S. Scheuermayer, E. V. Peresypkina, A. V. Virovets, M. Neumeier, R. Gschwind, M. Scheer, Angew. Chem. Int. Ed., 2013, 52, 10896-10899.

[Ag(η²?As₄)₂]⁺[pftb]⁻ can be used to store yellow arsenic (As₄). From it, As₄ can be easily released to give concentrated, light-stable solutions. These As₄ solutions, and those of white phosphorus (P₄), allowed molecular As₄ and P₄ to be encapsulated inside giant, spherical aggregates and polymeric matrices, enabling the first determination of their E-E (E=P, As) bond lengths by diffraction methods.

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Detection of the Elusive Highly Charged Zintl Ions Si₄⁴⁻ and Sn₄⁴⁻ in Liquid Ammonia by NMR Spectroscopy

M. Neumeier, F. Fendt, S. Gärtner, C. Koch, T. Gärtner, N. Korber, R. M. Gschwind, Angew. Chem. Int. Ed., 2013, 52, 4483-4486.

The existence of the prototypical Zintl ions Tt₄⁴⁻ (Tt=Group-14 element), which are isoelectronic to the P₄ molecule, used to be confined to the solid state. Recently, circumstantial evidence for a solution chemistry in liquid ammonia emerged. Direct spectroscopic observation of the dissolved anions has now been achieved. In the case of Si₄⁴⁻, this is the first solution detection of any homoatomic silicide.

For further publications see publication list.