Birgit Gerke

The Role of 2,6-Diaminopyridine Ligands in the Isolation of an Unprecedented, Low-Valent Tin Complex

Stabilization of the central atom in an oxidation state of zero through coordination of neutral ligands is a common bonding motif in transition-metal chemistry. However, the stabilization of main-group elements in an oxidation state of zero by neutral ligands is rare. Herein, we report that the transamination reaction of the DAMPY ligand system (DAMPY=2,6-[ArNH-CH2 ]2 (NC5 H3 ) (Ar=C6 H3 -2,6-iPr2 )) with Sn[N(SiMe3 )2 ]2 produces the DIMPYSn complex (DIMPY=(2,6-[ArNCH]2 (NC5 H3 )) with the Sn atom in a formal oxidation state of zero. This is the first example of a tin compound stabilized in a formal oxidation state of zero by only one donor molecule. Furthermore, three related low-valent Sn(II) complexes, including a [DIMPYSn(II) Cl](+) [SnCl3 ](-) ion pair, a bisstannylene DAMPY{Sn(II) [N(SiMe3 )2 ]2 }2 , and the enamine complex MeDIMPYSn(II) , were isolated. Experimental results and the conclusions drawn are also supported by theoretical studies at the density functional level of theory and (119) Sn Mössbauer spectroscopy.

Inorganic Double Helices in Semiconducting SnIP

SnIP is the first atomic-scale double helical semiconductor featuring a 1.86 eV bandgap, high structural and mechanical flexibility, and reasonable thermal stability up to 600 K. It is accessible on a gram scale and consists of a racemic mixture of right- and left-handed double helices composed by [SnI] and [P] helices. SnIP nanorods <20 nm in diameter can be accessed mechanically and chemically within minutes.

Redox-Active N-Heterocyclic Germylenes and Stannylenes with a Ferrocene-1,1'-diyl Backbone

We describe ferrocene-based N-heterocyclic germylenes and stannylenes of the type [Fe{(η5 -C5 H4 )NR}2 E:] (1 RE; E=Ge, Sn; R=neopentyl (Np), mesityl (Mes), trimethylsilyl (TMS)), which constitute the first examples of redox-functionalised N-heterocyclic tetrylenes (NHTs). These compounds are thermally stable and were structurally characterised by means of X-ray diffraction studies, except for the neopentyl-substituted stannylene 1 NpSn, the decomposition of which afforded the aminoiminoferrocene [fc(NHCH2 tBu)(N=CHtBu)] (2) and the spiro tin(IV) compound (1 Np)2 Sn (3). DFT calculations show that the HOMO of the NHTs of our study is localised on the ferrocenylene backbone. A one-electron oxidation process affords ions of the type 1 RE+. . In contrast to the NHC system 1 RC, the localised ferrocenium-type nature of the oxidised form does not compromise the fundamental tetrylene character of 1 RE+. .

Ferrocenyl-Functionalized Sn/Se and Sn/Te Complexes: Synthesis, Reactivity, Optical, and Electronic Properties

An adamantane-shaped, ferrocenyl-substituted tin selenide complex, [(FcSn)4Se6] (1; Fc = ferrocenyl), and a ferrocenyl-substituted tin telluride five-membered ring, [(Fc2Sn)3Te2] (2), were obtained upon treatment of FcSnCl3 with K2E (E = Se, Te). Complex 1 further reacts with Na2S·9H2O and [Cu(PPh3)3Cl] to form a ternary complex, [(CuPPh3)6(S/Se)6(SnFc)2] (3). We discuss structures, optical and electrochemical properties as well as Mössbauer spectra.

Chemistry of stannylene-based Lewis pairs: dynamic tin coordination switching between donor and acceptor character.

The coordination chemistry of cyclic stannylene-based intramolecular Lewis pairs is presented. The P→Sn adducts were treated with [Ni(COD)2] and [Pd(PCy3)2] (COD = 1,5-cyclooctadiene, PCy3 = tricyclohexylphosphine). In the isolated coordination compounds the stannylene moiety acts either as an acceptor or a donor ligand. Examples of a dynamic switch between these two coordination modes of the P-Sn ligand are illustrated and the structures in the solid state together with heteronuclear NMR spectroscopic findings are discussed. In the case of a Ni(0) complex, (119)Sn Mössbauer spectroscopy of the uncoordinated and coordinated phosphastannirane ligand is presented.

Sr2Au6Al3 and Eu2Au6Al3 – First Representatives of the Sr2Au6Zn3 Type with Aluminum Triangles

The aluminides Sr2Au6Al3 and Eu2Au6Al3 were synthesized by melting the elements in sealed tantalum tubes in a muffle or induction furnace. The samples were characterized by powder and single-crystal X-ray diffraction: Sr2Au6Zn3 type, R3̄c, a = 845.1(1), c = 2177.2(3) pm, wR2=0.0263, 520 F2 values, 20 variables for Sr2Au6.18(1)Al2.82(1), and a = 838.0(1), c = 2177.1(7) pm, wR2 = 0.0276, 510 F2 values, 19 variables for Eu2Au6Al3. The gold atoms build up diamond-related networks of slightly distorted tetrahedra in the stacking sequence of the 6R polytype (289 - 296 pm Au-Au in Eu2Au6Al3). The voids left by this network are filled in an ordered manner by strontium (europium) atoms and the rare motif of Al3 triangles (286 pm Al-Al in Eu2Au6Al3). The Al3 triangles in Sr2Au6.18(1)Al2.82(1) show a small degree of Al/Au mixing. Graphical Abstract Sr2Au6Al3 and Eu2Au6Al3 – First Representatives of the Sr2Au6Zn3 Type with Aluminum Triangles

Intricate Short-Range Ordering and Strongly Anisotropic Transport Properties of Li1–xSn2+xAs2

A new ternary compound, Li(1-x)Sn(2+x)As2, 0.2 < x < 0.4, was synthesized via solid-state reaction of elements. The compound crystallizes in a layered structure in the R3̅m space group (No. 166) with Sn-As layers separated by layers of jointly occupied Li/Sn atoms. The Sn-As layers are comprised of Sn3As3 puckered hexagons in a chair conformation that share all edges. Li/Sn atoms in the interlayer space are surrounded by a regular As6 octahedron. Thorough investigation by synchrotron X-ray and neutron powder diffraction indicate no long-range Li/Sn ordering. In contrast, the local Li/Sn ordering was revealed by synergistic investigations via solid-state (6,7)Li NMR spectroscopy, HRTEM, STEM, and neutron and X-ray pair distribution function analyses. Due to their different chemical natures, Li and Sn atoms tend to segregate into Li-rich and Sn-rich regions, creating substantial inhomogeneity on the nanoscale. The inhomogeneous local structure has a high impact on the physical properties of the synthesized compounds: the local Li/Sn ordering and multiple nanoscale interfaces result in unexpectedly low thermal conductivity and highly anisotropic resistivity in Li(1-x)Sn(2+x)As2.

Reactions with a Metalloid Tin Cluster {Sn10[Si(SiMe3)3]4}2−: Ligand Elimination versus Coordination Chemistry

Chemistry that uses metalloid tin clusters as a starting material is of fundamental interest towards understanding the reactivity of such compounds. Since we identified {Sn10[Si(SiMe3)3]4}(2-) 7 as an ideal candidate for such reactions, we present a further step in the understanding of metalloid tin cluster chemistry. In contrast to germanium chemistry, ligand elimination seems to be a major reaction channel, which leads to the more open metalloid cluster {Sn10[Si(SiMe3)3]3}(-) 9, in which the Sn core is only shielded by three Si(SiMe3)3 ligands. Compound 9 is obtained through different routes and is crystallised together with two different countercations. Besides the structural characterisation of this novel metalloid tin cluster, the electronic structure is analysed by (119)Sn Mössbauer spectroscopy. Additionally, possible reaction pathways are discussed. The presented first step into the chemistry of metalloid tin clusters thus indicates that, with respect to metalloid germanium clusters, more reaction channels are accessible, thereby leading to a more complex reaction system.

The gallium intermetallics REPdGa3 (RE = La, Ce, Pr, Nd, Sm, Eu) with SrPdGa3-type structure

Abstract The gallium-rich intermetallic phases REPdGa3 (RE=La, Ce, Pr, Nd, Sm, Eu) were obtained by arc-melting of the elements and subsequent annealing for crystal growth. The samples were studied by X-ray diffraction on powders and single crystals. The structures of three crystals were refined from X-ray diffractometer data: SrPdGa3 type, Cmcm, a=634.3(1), b=1027.2(1), c=593.5(1) pm, wR=0.0621, 380 F2 values, 20 variables for CePd0:80(4)Ga3:20(4), a=635.9(1), b=1027.5(1), c=592.0(1) pm, wR=0.1035, 457 F2 values, 19 variables for CePdGa3, and a=640.7(1), b=1038.2(1), c=593.7(1) pm, wR=0.0854, 489 F2 values, 19 variables for EuPdGa3. The REPdGa3 gallides are orthorhombic superstructure variants of the aristotype ThCr2Si2. The palladium and gallium atoms build up polyanionic [PdGa3]δ- networks with Pd-Ga and Ga-Ga distances of 248 - 254 and 266 - 297 pm, respectively, in EuPdGa3. The rare earth atoms fill cavities within the polyanionic networks. They are coordinated by five palladium and twelve gallium atoms. Taking CePdGa3 as an illustrative representative, the band structure calculations show largely dispersive itinerant s, p bands and little dispersive d (Pd) and f (Ce) bands, the latter crossing the Fermi level at large magnitude leading to magnetic instability in a spin-degenerate state and a subsequent antiferromagnetic ground state with a small moment of ±0.36 μB on Ce. The bonding characteristics indicate a prevailing Ce-Ga bonding versus Pd-Ga and Ce-Pd. Temperature-dependent magnetic susceptibility and 151Eu Mössbauer spectroscopic measurements point to stable trivalent lanthanum, cerium, praseodymium, and neodymium, but divalent europium. SmPdGa3 shows intermediate valence. Antiferromagnetic ordering occurs at TN =5.1(5), 7.0(5), 6.3(5), 11.9(5), and 23.0(5) for RE=Ce, Pr, Nd, Sm, and Eu, respectively.

Magnetism and Magnetocaloric Effect in EuAuZn

The magnetic properties and magnetocaloric effect (MCE) in the ternary intermetallic compound EuAuZn have been studied via magnetization and heat capacity measurements. The compound orders ferromagnetically below T_C ~ 52 K with a spin reorientation transition at T_SR ~ 19 K. A large reversible MCE has been observed in EuAuZn accompanied by a second-order magnetic phase transition from a paramagnetic to a ferromagnetic state. Under a field change of 5 T, the maximum values of magnetic entropy change (-ΔS_M^max) and adiabatic temperature change (ΔT_ad^max) are 9.1 J/kg·K and 3.8 K, respectively, the corresponding relative cooling power is 318 J/kg.