Syntheses, Structures, and Comprehensive NMR Spectroscopic Investigations of Hetero-Chalcogenidometallates: The Right Mix toward Multinary Complexes

Current advances in tin cluster chemistry

This perspective summarizes highlights and most recent advances in tin cluster chemistry, thereby addressing the whole diversity of (mostly) discrete units containing tin atoms. Although being a (semi-)metallic element, tin is in the position to occur both in formally positive or negative oxidation states in these molecules, which causes a broad range of fundamentally different properties of the corresponding compounds. Tin(iv) compounds are not as oxophilic and not as prone to hydrolysis as related Si or Ge compounds, hence allowing for easier handling and potential application. Nevertheless, their reactivity is high due to an overall reduction of bond energies, which makes tin clusters interesting candidates for functional compounds. Beside aspects that point towards bioactivity or even medical applications, materials composed of naked or ligand-protected tin clusters, with or without bridging ligands, show interesting optical, and ion/molecule-trapping properties.

Recent advances in the self-assembly of polynuclear metal–selenium and –tellurium compounds from 14–16 reagents

The use of reagents containing bonds between group 14 elements and Se or Te for the self-assembly of polynuclear metal–chalcogen compounds is covered. Background material is briefly reviewed and examples from the literature are highlighted from the period 2007–2017. Emphasis is placed on the different classes of 14–16 precursors and their application in the targeted synthesis of metal–chalcogen compounds. The unique properties arising from the combination of specific 14–16 precursors, metal atoms, and ancillary ligands are also described. Selected examples are chosen to underline the progress in (i) controlled synthesis of heterometallic (ternary) chalcogen clusters, (ii) chalcogen clusters with organic functionalized surfaces, and (iii) crystalline open-framework metal chalcogenides.

Monodisperse Ultrasmall Manganese-Doped Multimetallic Oxysulfide Nanoparticles as Highly Efficient Oxygen Reduction Electrocatalyst

The highly efficient and cheap non-Pt-based electrocatalysts such as transition-based catalysts prepared via facile methods for oxygen reduction reaction (ORR) are desirable for large-scale practical industry applications in energy conversion and storage systems. Herein, we report a straightforward top-down synthesis of monodisperse ultrasmall manganese-doped multimetallic (ZnGe) oxysulfide nanoparticles (NPs) as an efficient ORR electrocatalyst by simple ultrasonic treatment of the Mn-doped Zn-Ge-S chalcogenidometalate crystal precursors in H₂O/EtOH for only 1 h at room temperature. Thus obtained ultrasmall monodisperse Mn-doped oxysulfide NPs with ultralow Mn loading level (3.92 wt %) not only exhibit comparable onset and half-wave potential (0.92 and 0.86 V vs reversible hydrogen electrode, respectively) to the commercial 20 wt % Pt/C but also exceptionally high metal mass activity (189 mA/mg at 0.8 V) and good methanol tolerance. A combination of transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical analysis demonstrated that the homogenous distribution of a large amount of Mn(III) on the surface of NPs mainly accounts for the high ORR activity. We believe that this simple synthesis of Mn-doped multimetallic (ZnGe) oxysulfide NPs derived from chalcogenidometalates will open a new route to explore the utilization of discrete-cluster-based chalcogenidometalates as novel non-Pt electrocatalysts for energy applications and provide a facile way to realize the effective reduction of the amount of catalyst while keeping desired catalytic performances.

Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of Chalcogenidoplumbates(II or IV)

The phases of "PbCh2" (Ch = Se, Te) are obtained from solid-state syntheses (i.e., by the fusion of the elements under inert conditions in silica glass ampules). Reduction of such phases by elemental alkaline metals in amines affords crystalline chalcogenidoplumbate(II) salts comprised of [PbTe3]^2- or [Pb2Ch3]^2- anions, depending upon which sequestering agent for the cations is present: crown ethers, like 18-crown-6, or cryptands, like [2.2.2]crypt. Reactions of solutions of such anions with transition-metal compounds yield (poly-)chalcogenide anions or transition-metal chalcogenide clusters, including one with a µ-PbSe ligand (i.e., the heaviest-known CO homolog). In contrast, the solid-state synthesis of a phase of the nominal composition "K2PbSe2" by successive reactions of the elements and by the subsequent solvothermal treatment in amines yields the first non-oxide/halide inorganic lead(IV) compound: a salt of the ortho-selenidoplumbate(IV) anion [PbSe4]^4-. This was unexpected due to the redox potentials of Pb(IV) and Se(-II). Such methods can further be applied to other elemental combinations, leading to the formation of solutions with binary [HgTe2]^2- or [BiSe3]^3- anions, or to large-scale syntheses of K2Hg2Se3 or K3BiSe3 via the solid-state route. All compounds are characterized by single-crystal X-ray diffraction and elemental analysis; solutions of plumbate salts can be investigated by ²⁰⁵Pb and ⁷⁷Se or ¹²⁷Te NMR techniques. Quantum chemical calculations using density functional theory methods enable energy comparisons. They further allow for insights into the electronic configuration and thus, the bonding situation. Molecular Rh-containing Chevrel-type compounds were found to exhibit delocalized mixed valence, whereas similar telluridopalladate anions are electron-precise; the cluster with the µ-PbSe ligand is energetically favored over a hypothetical CO analog, in line with the unsuccessful attempt at its synthesis. The stability of formal Pb(IV) within the [PbSe4]^4- anion is mainly due to a suitable stabilization within the crystal lattice.

Smallest molecular chalcogenidometalate anions of the heaviest metals: syntheses, structures, and their interconversion

The syntheses of the first molecular meta-selenidomercurate(ii), ortho-telluridothallate(iii) and a hydrate of an ortho-selenidoplubate(iv) are presented alongside an improved and facile synthesis of the selenidobismuthate(iii) with almost quantitative yields. By means of quantum chemical calculations, the energetics of the interconversions of small metalate anions is discussed and the existence of the heaviest homologues of [NO2](-), [NO3](-), [PO4](2-) and [CO3](2-) are predicted.

Atomistic description of thiostannate-capped CdSe nanocrystals: retention of four-coordinate SnS4 motif and preservation of Cd-rich stoichiometry

Colloidal semiconductor nanocrystals (NCs) are widely studied as building blocks for novel solid-state materials. Inorganic surface functionalization, used to displace native organic capping ligands from NC surfaces, has been a major enabler of electronic solid-state devices based on colloidal NCs. At the same time, very little is known about the atomistic details of the organic-to-inorganic ligand exchange and binding motifs at the NC surface, severely limiting further progress in designing all-inorganic NCs and NC solids. Taking thiostannates (K4SnS4, K4Sn2S6, K6Sn2S7) as typical examples of chalcogenidometallate ligands and oleate-capped CdSe NCs as a model NC system, in this study we address these questions through the combined application of solution (1)H NMR spectroscopy, solution and solid-state (119)Sn NMR spectroscopy, far-infrared and X-ray absorption spectroscopies, elemental analysis, and by DFT modeling. We show that through the X-type oleate-to-thiostannate ligand exchange, CdSe NCs retain their Cd-rich stoichiometry, with a stoichiometric CdSe core and surface Cd adatoms serving as binding sites for terminal S atoms of the thiostannates ligands, leading to all-inorganic (CdSe)core[Cdm(Sn2S7)yK(6y-2m)]shell (taking Sn2S7(6-) ligand as an example). Thiostannates SnS4(4-) and Sn2S7(6-) retain (distorted) tetrahedral SnS4 geometry upon binding to NC surface. At the same time, experiments and simulations point to lower stability of Sn2S6(4-) (and SnS3(2-)) in most solvents and its lower adaptability to the NC surface caused by rigid Sn2S2 rings.

Synthesis and structures of 1,3-bis(organochalcogenyl) distannatrisilabicyclo[1.1.1]pentanes

The heteronuclear [1.1.1]propellane Sn2Si3Mes6 (1; Mes = 2,4,6-Me3C6H2) was reacted with the dichalcogenyl compounds PhE–EPh (E = S, Se, or Te) to furnish the 1,3-bis(organochalcogenyl) distannatrisilabicyclo[1.1.1]pentanes 3 (E = S), 4 (E = Se), and 5 (E = Te). The E–E bond addition reaction is reminiscent of the formation of FcS–Sn(SiMes2)3Sn–SFc (2; Fc = ferrocenyl) reported previously. Contrary to 2, for which it was shown that its formation can be enhanced by daylight, the analogous clusters 3–5 are very sensitive to light in solution. Solid samples are, however, stable for a prolonged period of time. All three compounds were characterized in detail, including X-ray structure analyses on single crystals of 3 and 5. The core structure connectivities of the clusters were fully confirmed by 119Sn, 77Se, and 125Te NMR spectroscopy, among others. In particular, the 117Sn–119Sn coupling constant between the formally nonbonded bridgehead tin atoms nicely correlates with the interbridgehead distance, i.e., a larger distance is associated with a smaller 117Sn–119Sn coupling constant, and vice versa. This coupling is mediated by so-called “back-lobe-to-back-lobe” interactions through cage. The detection of two different 77Se–119Sn and 125Te–119Sn couplings each (i.e., 1J and 2J) further supported these findings.

Mixed organotin(IV) chalcogenides: from molecules to Sn-S-Se semiconducting thin films deposited by spin-coating

Put the right spin on it: Mixed monomeric organotin(IV) chalcogenides of the general formula L(2)Sn(2)EX(2) containing two terminal Sn-X (X = Se, Te) bonds were prepared and were tested as potential single-source precursors for the deposition of semiconducting thin films. Spin-coating deposition of [{2,6-(Me(2)NCH(2))(2)C(6)H(3)}SnSe](2)(μ-S), as the useful single-source precursor, provided amorphous Sn-S-Se semiconducting thin films.

Expanding the chemical versatility of colloidal nanocrystals capped with molecular metal chalcogenide ligands

We developed different strategies toward the synthesis of colloidal nanocrystals stabilized with molecular metal chalcogenide complexes (MCCs). Negatively charged MCCs, such as SnS(4)(4-), Sn(2)S(6)(4-), SnTe(4)(4-), AsS(3)(3-), MoS(4)(2-), can quantitatively replace the organic ligands at the nanocrystal surface and stabilize nanocrystal solutions in different polar media. We showed that all-inorganic nanocrystals composed of metals, semiconductors, or magnetic materials and capped with various MCC ligands can be synthesized using convenient and inexpensive chemicals and environmentally benign solvents such as water, formamide, or dimethylsulfoxide. The development of mild synthetic routes was found to be crucial for the design of highly luminescent all-inorganic nanocrystals, such as CdSe/ZnS and PbS capped with Sn(2)S(6)(4-) MCCs, respectively. We also prepared conductive and luminescent layer-by-layer assemblies from inorganically capped colloidal nanocrystals and polyelectrolytes. In close-packed films of 5-nm Au nanocrystals stabilized with Na(2)Sn(2)S(6) we observed very high electrical conductivities (>1000 S cm(-1)).