ChemInform Abstract: Endohedrally Filled [Ni@Sn9]4‐and [Co@Sn9]5‐Clusters in the Neat Solids Na12Ni1‐xSn17 and K13‐xCo1‐xSn17: Crystal Structure and 119Sn Solid‐State NMR Spectroscopy.

The title Zintl phases are prepared by reactions of the corresponding elemental alkali metals with pre‐prepared M‐Sn alloys (M: Ni, Co) at 550—880 °C for 48 h.     

The Neat Ternary Solid K5−xCo1−xSn9 with Endohedral [Co@Sn9]5− Cluster Units: A Precursor for Soluble Intermetalloid [Co2@Sn17]5− Clusters

A new type of Zintl phase is presented that contains endohedrally filled clusters and that allows for the formation of intermetalloid clusters in solution by a one‐step synthesis. The intermetallic compound K_5?xCo_1?xSn₉ was obtained by the reaction of a preformed Co? Sn alloy with potassium and tin at high temperatures. The diamagnetic saltlike ternary phase contains discrete [Co@Sn₉]^5? clusters that are separated by K⁺ ions. The intermetallic compound K_5?xCo_1?xSn₉ readily and incongruently dissolves in ethylenediamine and in the presence of 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane (2.2.2‐crypt), thereby leading to the formation of crystalline [K([2.2.2]crypt)]₅[Co₂Sn₁₇]. The novel polyanion [Co₂Sn₁₇]^5? contains two Co‐filled Sn₉ clusters that share one vertex. Both compounds were characterized by single‐crystal X‐ray structure analysis. The diamagnetism of K_5?xCo_1?xSn₉ and the paramagnetism of [K([2.2.2]crypt)]₅[Co₂Sn₁₇] have been confirmed by superconducting quantum interference device (SQUID) and EPR measurements, respectively. Quantum chemical calculations reveal an endohedral Co^1? atom in an [Sn₉]^4? nido cluster for [Co@Sn₉]^5? and confirm the stability of the paramagnetic [Co₂Sn₁₇]^5? unit.     

Charged Si9 Clusters in Neat Solids and the Detection of [H2Si9]2− in Solution: A Combined NMR,Raman, Mass Spectrometric,and Quantum Chemical Investigation

Polyanionic silicon clusters are provided by the Zintl phases K₄Si₄, comprising [Si₄]⁴⁻ units, and K₁₂Si₁₇, consisting of [Si₄]⁴⁻ and [Si₉]⁴⁻ clusters. A combination of solid‐state MAS‐NMR, solution NMR, and Raman spectroscopy, electrospray ionization mass spectrometry, and quantum‐chemical investigations was used to investigate four‐ and nine‐atomic silicon Zintl clusters in neat solids and solution. The results were compared to ²⁹Si isotope‐enriched samples. ²⁹Si‐MAS NMR and Raman shifts of the phase‐pure solids K₄Si₄ and K₁₂Si₁₇ were interpreted by quantum‐chemical calculations. Extraction of [Si₉]⁴⁻ clusters from K₁₂Si₁₇ with liquid ammonia/222crypt and their transfer to pyridine yields in a red solid containing Si₉ clusters. This compound was characterized by elemental and EDX analyses and ²⁹Si‐MAS NMR and Raman spectroscopy. Charged Si₉ clusters were detected by ²⁹Si NMR in solution. ²⁹Si and ¹H NMR spectra reveal the presence of the [H₂Si₉]²⁻ cluster anion in solution.     

Metallocages for Metal Anions: Highly Charged [Co@Ge9]5− and [Ru@Sn9]6− Clusters Featuring Spherically Encapsulated Co1− and Ru2− Anions

Endohedral clusters count as molecular models for intermetallic compounds—a class of compounds in which bonding principles are scarcely understood. Herein we report soluble cluster anions with the highest charges on a single cluster to date. The clusters reflect the close analogy between intermetalloid clusters and corresponding coordination polyhedra in intermetallic compounds. We now establish Raman spectroscopy as a reliable probe to assign for the first time the presence of discrete, endohedrally filled clusters in intermetallic phases. The ternary precursor alloys with nominal compositions “K₅Co_1.2Ge₉” and “K₄Ru₃Sn₇” exhibit characteristic bonding modes originating from metal atoms in the center of polyhedral clusters, thus revealing that filled clusters are present in these alloys. We report also on the structural characterization of [Co@Ge₉]^5? ( 1a ) and [Ru@Sn₉]^6? ( 2a ) obtained from solutions of the respective alloys.     

Binary alkali metal compounds with the zintl anions [Ge9]4− and [Sn9]4−

The binary germanides M₁₂Ge₁₇ and M₄Ge₉ (M ? Na, K, Rb, Cs) and the stannides M₁₂Sn₁₇ and M₄Sn₉ (M ? K, Rb, Cs) were identified by a combination of direct synthesis, thermogravimetric analysis, vibrational spectroscopy, X-ray powder data and single crystal structure analysis. The M₁₂E₁₇ phases contain the cluster anions [E₉]^4? and [E₄]^4? in the ratio 1:2, forming a hierarchical structure with the cluster anions at the atomic positions of the hexagonal Laves phase MgZn₂. Like the M₄E₄ phases, the M₄Ge₉ compounds are hierarchical derivatives of the cubic Cr₃Si structure but with [Ge₉]^4? anions. The thermogravimetric analyses give strong evidence for the existence of at least one more phase with [E₉]^4? and [E₄]^4? clusters and of the clathrate phases M₆E₁₃₆ in addition to the well-known M₈E₄₄□₂ chlathrates.     

Origin and Location of Electrons and Protons during the Formation of Intermetalloid Clusters [Sm@Ga3−xH3−2xBi10+x]3− (x=0, 1)

Reaction of [GaBi₃]^2? with [Sm(C₅Me₄H)₃] yielded the first protonated ternary intermetalloid clusters [Sm@Ga_3?xH_3?2xBi_10+x]^3? ( 1 ; x=0,1). The presence of the Ga? H bonds and the transfer of electrons and protons during the formation of 1 were elucidated by a combination of experimental and quantum chemical methods, thereby rationalizing the role of the solvent ethane‐1,2‐diamine as a Brønsted acid. As an organic by‐product, we observed the previously unknown octamethylfulvene ( 2 ) upon C? C coupling of (C₅Me₄H)^?.     

The Solid Solution Sr1−xBaxGa2: Substitutional Disorder and Chemical Bonding Visited by NMR Spectroscopy and Quantum Mechanical Calculations

Complete miscibility of the intermetallic phases (IPs) SrGa₂ and BaGa₂ forming the solid solution Sr_1?xBa_xGa₂ is shown by means of X‐ray diffraction, thermoanalytical and metallographic studies. Regarding the distances of Sr/Ba sites versus substitution degree, a model of isolated substitution centres (ISC) for up to 10 % cation substitution is explored to study the influence on the Ga bonding situation. A combined application of NMR spectroscopy and quantum mechanical (QM) calculations proves the electric field gradient (EFG) to be a sensitive measure of different bonding situations. The experimental resolution is boosted by orientation‐dependent NMR on magnetically aligned powder samples, revealing in first approximation two different Ga species in the ISC regimes. EFG calculations using superlattice structures within periodic boundary conditions are in fair agreement with the NMR spectroscopy data and are discussed in detail regarding their application on disordered IPs.     

Direct Detection of 17O in [Gd(DOTA)]− by NMR Spectroscopy

The ¹⁷O NMR spectrum of the non‐coordinated carboxyl oxygen in the Gd^III–DOTA (DOTA=tetraazacyclododecanetetraacetic acid) complex has been observed experimentally. Its line width is essentially unaffected by paramagnetic relaxation due to gadolinium, and is only affected by the quadrupole pathway. The results are supported by the relevant parameters (hyperfine and quadrupole coupling constants) calculated by relativistic DFT methods. This finding opens up new avenues for investigating the structure and reactivity of paramagnetic Gd^III complexes used as contrast agents in magnetic resonance imaging.     

Heterometallic Clusters [CuSn3S9]5− and [Cu6Sn6S20]10−: Solvothermal Synthesis and Characterization of 4f–3d Thiostannates

Two types of 4f–3d thiostannates with general formula [Hen]₂[Ln(en)₄(CuSn₃S₉)] ? 0.5 en ( Ln1 ; Ln=La, 1 ; Ce, 2 ) and [Hen]₄[Ln(en)₄]₂[Cu₆Sn₆S₂₀] ? 3 en ( Ln2 ; Ln=Nd, 3 ; Gd, 4 ; Er, 5 ) were prepared by reactions of Ln₂O₃, Cu, Sn, and S in ethylenediamine (en) under solvothermal conditions between 160 and 190 °C. However, reactions performed in the range from 120 to 140 °C resulted in crystallization of [Sn₂S₆]^4? compounds and CuS powder. In 1 and 2 , three SnS₄ tetrahedra and one CuS₃ triangle are joined by sharing sulfur atoms to form a novel [CuSn₃S₉]^5? cluster that coordinates to the Ln³⁺ ion of [Ln(en)₄]³⁺ (Ln=La, Ce) as a monodentate ligand. The [CuSn₃S₉]^5? unit is the first thio‐based heterometallic adamantane‐like cluster coordinating to a lanthanide center. In 3 – 5 , six SnS₄ tetrahedra and six CuS₃ triangles are connected by sharing common sulfur atoms to form the ternary [Cu₆Sn₆S₂₀]^10? cluster, in which a Cu₆ core is enclosed by two Sn₃S₁₀ fragments. The topological structure of the novel Cu₆ core can be regarded as two Cu₄ tetrahedra joined by a common edge. The Ln³⁺ ions in Ln1 and Ln2 are in nine‐ and eightfold coordination, respectively, which leads to the formation of the [CuSn₃S₉]^5? and [Cu₆Sn₆S₂₀]^10? clusters under identical synthetic conditions. The syntheses of Ln1 and Ln2 show the influence of the lanthanide contraction on the quaternary Ln/Cu/Sn/S system in ethylenediamine. Compounds 1 – 5 exhibit bandgaps in the range of 2.09–2.48 eV depending on the two different types of clusters in the compounds. Compounds 1 , 3 , and 4 lost their organic components in the temperature range of 110–350 °C by multistep processes.     

Cluster Fusion: Face‐Fused Nine‐Atom Deltahedral Clusters in [Sn14Ni(CO)]4−

The title anion was synthesized by heating dimethylformamide (DMF) solution of the known Ni‐centered and Ni(CO)‐capped tin clusters [Ni@Sn₉Ni(CO)]^3?. The new anion represents the first example of face‐fused nine‐atom molecular clusters. The two clusters are identical elongated tricapped trigonal prisms of nido‐[Sn₈Ni(CO)]^6? with nickel at one of the capping positions. They are fused along a triangular face adjacent to a trigonal prismatic base and made of two Sn and one Ni atoms. The new anion is structurally characterized by single‐crystal X‐ray diffraction in the compound (K[222‐crypt])₄[Sn₁₄Ni(CO)]?DMF. Its presence in solution is corroborated by electrospray mass spectrometry.     

Unravelling Local Atomic Order of the Anionic Sublattice in M(Al1−xGax)4 with M=Sr and Ba by Using NMR Spectroscopy and Quantum Mechanical Modelling

The quasibinary section of the intermetallic phases MAl₄ and MGa₄ with M=Sr and Ba have been characterised by means of X‐ray diffraction (XRD) studies and differential thermal analysis. The binary phases show complete miscibility and form solid solutions M(Al_1?xGa_x)₄ with M=Sr and Ba. These structures crystallise in the BaAl₄ structure type with four‐ and five‐bonded Al and/or Ga atoms (denoted as Al(4b), Al(5b), Ga(4b), and Ga(5b), respectively) that form a polyanionic Al/Ga sublattice. Solid state ²⁷Al NMR spectroscopic analysis and quantum mechanical (QM) calculations were applied to study the bonding of the Al centres and the influence of Al/Ga substitution, especially in the regimes with low degrees of substitution. M(Al_1?xGa_x)₄ with M=Sr and Ba and 0.925≤x≤0.975 can be described as a matrix of the binary majority compound in which a low amount of the Ga atoms has been substituted by Al atoms. In good agreement with the QM calculations, ²⁷Al NMR investigations and single crystal XRD studies prove a preferred occupancy of Al(4b) for these substitution regimes. Furthermore, two different local Al environments were found, namely isolated Al(4b1) atoms and Al(4b2), due to the formation of Al(4b)–Al(4b) pairs besides isolated Al(4b) atoms within the polyanionic sublattice. QM calculations of the electric field gradient (EFG) using superlattice structures under periodic boundary conditions are in good agreement with the NMR spectroscopic results.     

Stacking Structure of Confined 1‐Butanol in SBA‐15 Investigated by Solid‐State NMR Spectroscopy

Understanding the complex thermodynamic behavior of confined amphiphilic molecules in biological or mesoporous hosts requires detailed knowledge of the stacking structures. Here, we present detailed solid‐state NMR spectroscopic investigations on 1‐butanol molecules confined in the hydrophilic mesoporous SBA‐15 host. A range of NMR spectroscopic measurements comprising of ¹H spin–lattice (T₁), spin–spin (T₂) relaxation, ¹³C cross‐polarization (CP), and ¹H,¹H two‐dimensional nuclear Overhauser enhancement spectroscopy (¹H,¹H 2D NOESY) with the magic angle spinning (MAS) technique as well as static wide‐line ²H NMR spectra have been used to investigate the dynamics and to observe the stacking structure of confined 1‐butanol in SBA‐15. The results suggest that not only the molecular reorientation but also the exchange motions of confined molecules of 1‐butanol are extremely restricted in the confined space of the SBA‐15 pores. The dynamics of the confined molecules of 1‐butanol imply that the ¹H,¹H 2D NOESY should be an appropriate technique to observe the stacking structure of confined amphiphilc molecules. This study is the first to observe that a significant part of confined 1‐butanol molecules are orientated as tilted bilayered structures on the surface of the host SBA‐15 pores in a time‐average state by solid‐state NMR spectroscopy with the ¹H,¹H 2D NOESY technique.     

Atomistic Characterisation of Li+ Mobility and Conductivity in Li7−xPS6−xIx Argyrodites from Molecular Dynamics Simulations,Solid‐State NMR,and Impedance Spectroscopy

The atomistic mechanisms of Li⁺ ion mobility/conductivity in Li_7?xPS_6?xI_x argyrodites are explored from both experimental and theoretical viewpoints. Ionic conductivity in the title compound is associated with a solid–solid phase transition, which was characterised by low‐temperature differential scanning calorimetry, ⁷Li and ¹²⁷I NMR investigations, impedance measurements and molecular dynamics simulations. The NMR signals of both isotopes are dominated by anisotropic interactions at low temperatures. A significant narrowing of the NMR signal indicates a motional averaging of the anisotropic interactions above 177±2 K. The activation energy to ionic conductivity was assessed from both impedance spectroscopy and molecular dynamics simulations. The latter revealed that a series of interstitial sites become accessible to the Li⁺ ions, whilst the remaining ions stay at their respective sites in the argyrodite lattice. The interstitial positions each correspond to the centres of tetrahedra of S/I atoms, and differ only in terms of their common corners, edges, or faces with adjacent PS₄ tetrahedra. From connectivity analyses and free‐energy rankings, a specific tetrahedron is identified as the key restriction to ionic conductivity, and is clearly differentiated from local mobility, which follows a different mechanism with much lower activation energy. Interpolation of the lattice parameters as derived from X‐ray diffraction experiments indicates a homogeneity range for Li_7?xPS_6?xI_x with 0.97≤x≤1.00. Within this range, molecular dynamics simulations predict Li⁺ conductivity at ambient conditions to vary considerably.     

Probing Transient Conformational States of Proteins by Solid‐State R1ρ Relaxation‐Dispersion NMR Spectroscopy

The function of proteins depends on their ability to sample a variety of states differing in structure and free energy. Deciphering how the various thermally accessible conformations are connected, and understanding their structures and relative energies is crucial in rationalizing protein function. Many biomolecular reactions take place within microseconds to milliseconds, and this timescale is therefore of central functional importance. Here we show that R_1ρ relaxation dispersion experiments in magic‐angle‐spinning solid‐state NMR spectroscopy make it possible to investigate the thermodynamics and kinetics of such exchange process, and gain insight into structural features of short‐lived states.     

Step‐by‐Step Synthesis of the Endohedral Stannaspherene [Ir@Sn12]3− via the Capped Cluster Anion [Sn9Ir(cod)]3−

The endohedral stannaspherene cluster anion [Ir@Sn₁₂]^3? was synthesized in two steps. The reaction of K₄Sn₉ with [IrCl(cod)]₂ (cod: 1,5‐cyclooctadienyl) in ethylenediamine (en) solution first yielded the [K(2,2,2‐crypt)]⁺ salt (2,2,2‐crypt: 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane) of the capped cluster anion [Sn₉Ir(cod)]^3?. Subsequently, crystals of this compound were dissolved in en, followed by the addition of triphenylphosphine or 1,2‐bis(diphenylphosphino)ethane and treatment at elevated temperatures. [Ir@Sn₁₂]^3? was obtained and characterized as the [K(2,2,2‐crypt)]⁺ salt. The isolation of [Sn₉Ir(cod)]^3? as an intermediate product establishes that the formation of the stannaspherene [Ir@Sn₁₂]^3? occurs through the oxidation of [Sn₉Ir(cod)]^3?. Among the structurally characterized tetrel cluster anions, [Ir@Sn₁₂]^3? is a unique example of a stannaspherene, and one of the rare spherical clusters encapsulating a metal atom that is not a member of Group 10. Single‐crystal structure determination shows that the novel Zintl ion cluster has nearly perfect icosahedral I_h point symmetry.