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

The existence of [µ-HSi4 ]3- in liquid ammonia solutions is confirmed by 1 H and 29 Si 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.

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

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@Sn6 Sb6 ]3- (1), [Co2 @Sn5 Sb7 ]3- (2), and [Ni2 @Sn7 Sb5 ]3- (3) were synthesized, which have pseudo-C4v -symmetric or pseudo-D4h -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 119 Sn NMR studies in solution, supported by quantum-chemical calculations of the shifts, illustrate the complexity regarding Sn:Sb distributions of such ternary systems.

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

We report on the first unambiguous detection of the elusive [HSi9 ]3- anion in solutions of liquid ammonia by various 29 Si and 1 H NMR experiments including chemical exchange saturation transfer (CEST). The characteristic multiplicity patterns of both the 29 Si and 1 H resonances together with CEST and a partially reduced 1 H,29 Si 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.

PPh4Cl in aqueous solution - the aggregation behavior of an antagonistic salt.

The initial definition of hydrotropy by Neuberg in 1916 describes a hydrotrope as a molecule which enhances the solubilization of hydrophobic substances in water. Sodium dodecyl sulfate (SDS) and sodium xylene sulfonate (SXS) are typical representatives fulfilling this old definition. They are either surfactants with a critical micellar concentration (CMC) or hydrotropes in the current sense of the term, showing a minimum hydrotrope concentration (MHC), respectively. In the present contribution, we consider the antagonistic salt PPh4Cl as a hydrotrope. Surface tension measurements and solubilization experiments on a hydrophobic dye confirm the solubilization behavior of PPh4Cl, which is in-between the one of SDS and SXS. With the help of scattering techniques (DLS, SLS, SAXS), NMR and conductivity measurements, we show that in contrast to SDS as a hydrotrope with an inherent CMC, PPh4Cl does not exhibit mesoscale aggregation. Therefore, PPh4Cl can be classified rather as a hydrotrope in the modern sense, with an inherent MHC just as SXS.

cyclo-P4 Building Blocks: Achieving Non-Classical Fullerene Topology and Beyond.

The cyclo-P4 complexes [CpR Ta(CO)2 (η4 -P4 )] (CpR : Cp''=1,3-C5 H3 tBu2 , Cp'''=1,2,4-C5 H2 tBu3 ) turned out to be predestined for the formation of hollow spherical supramolecules with non-classical fullerene-like topology. The resulting assemblies constructed with CuX (X=Cl, Br) showed a highly symmetric 32-vertex core of solely four- and six-membered rings. In some supramolecules, the inner cavity was occupied by an additional CuX unit. On the other hand, using CuI, two different supramolecules with either peanut- or pear-like shapes and outer diameters in the range of 2-2.5 nm were isolated. Furthermore, the spherical supramolecules containing Cp''' ligands at tantalum are soluble in CH2 Cl2 . NMR spectroscopic investigations in solution revealed the formation of isomeric supramolecules owing to the steric hindrance caused by the third tBu group on the Cp''' ligand. In addition, a 2D coordination polymer was obtained and structurally characterized.

A nano-sized supramolecule beyond the fullerene topology.

The reaction of [Cp(Bn) Fe(η(5) -P5 )] (1) (Cp(Bn) =η(5) -C5 (CH2 Ph)5 ) with CuI selectively yields a novel spherical supramolecule (CH2 Cl2 )3.4 @[(Cp(Bn) FeP5 )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 CH2 Cl2 , and NMR spectroscopy reveals that the scaffold of the supramolecule remains intact in solution. In addition, a novel 2D polymer [{Cp(Bn) Fe(η(5) -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.