Wolfgang Bensch

In-situ monitoring of the formation of crystalline solids.

The processes occurring during the early stages of the formation of crystalline solids are not well understood thus preventing the rational synthesis of new solids. The investigation of the structure-forming processes is an enormous challenge for both analytical and theoretical methods because very small particles or aggregates with different chemical composition and different sizes must be probed, both before and during nucleation. Furthermore, these precursors are present in a complex and dynamic equilibrium. This Review gives a survey of the in-situ methods available for the study of the early stages of crystallization of solids and how they can help in the synthesis of metastable polymorphs, of transient intermediates, and/or precursors displaying new or improved properties. Examples of actual research demonstrate the necessity and potentials but also the limitations of in-situ monitoring of the formation of crystalline solids.

Investigation of SnSe, SnSe2, and Sn2Se3 alloys for phase change memory applications

SnSe, SnSe2, and Sn2Se3 alloys have been studied to explore their suitability as new phase change alloys for electronic memory applications. The temperature dependence of the structural and electrical properties of these alloys has been determined and compared with that of GeTe. A large electrical resistance contrast of more than five orders of magnitude is achieved for SnSe2 and Sn2Se3 alloys upon crystallization. X-ray diffraction measurements show that the transition in sheet resistance is accompanied by crystallization. The activation energy for crystallization of SnSe, SnSe2, and Sn2Se3 has been determined. The microstructure of these alloys has been investigated by atomic force microscopy measurements. X-ray reflection measurements reveal density increases of 5.0%, 17.0%, and 9.1% upon crystallization for the different alloys.

The Hydrothermal Synthesis, Crystal Structures and Thermal Stability of the Novel One- and Two-Dimensional Thioantimonate(III) Compounds [Co(tren)]Sb2S4 and [Ni(tren)]Sb2S4

Two novel thioantimonate(III) compounds [Co(C6H18N4)]Sb2S4 (1) and [Ni(C6H18N4)]Sb2S4 (2) were synthesised under solvothermal conditions by reacting the transition metal, Sb and S in a 50% solution of tris(2-aminoethyl)amine (tren). The use of a tetradentate amine yields incompletely shielded transition metal cations which in turn are able to form bonds to the sulfur atoms of thioantimonate(III) anions. Compound 1 crystallises in the orthorhombic space group Pbca, a = 13.886(3) A, b = 11.452(2) A, c = 20.549(4) A, V = 3268(1) A3, Z = 8 and compound 2 crystallises in the monoclinic space group P21/n, a = 6.906(1) A, b = 22.822(5) A, c = 10.347(2) A, β = 103.17(3)°, V = 1587.9(6) A3, Z = 4. The 2∝[Sb2S42−] anion in compound 1 is formed by an SbS3 and an SbS4 unit sharing a common corner. Two SbS4 units have a common edge to form an Sb2S2 heterocycle. Four such Sb2S2 rings are at the corners of a two-dimensional square-like net. Interconnection of the rings by SbS3 pyramids yields Sb10S10 rings with pores measuring 10·8.4 A in diameter. The pores are filled by the [Co(tren)]2+ cations. The [Co]2+ cation is in a trigonal bipyramidal environment of four N atoms of the tren ligand and one S atom of the SbS3 pyramid. The one-dimensional 1∝[Sb2S42−] chain anion in 2 is built by two corner-sharing SbS3 units. The [Ni]2+ cation is in an octahedral environment consisting of four N atoms of the tren ligand and two S atoms of the anion. An NiSb2S3 heteroring in a twist conformation is formed with an unusually large Ni−S(1)−Sb(1) angle of 121.73(3)°. For the [Co]2+ (d7) cation no significant energy differences can be expected for the trigonal bipyramidal and octahedral coordination, and due to the geometrical requirements of the tetradentate ligand the former environment is preferred. In contrast, for [Ni]2+ (d8) an octahedral environment is energetically favoured over the trigonal bipyramidal arrangement. Both compounds start to decompose under an Ar atmosphere at about 250 °C. For 1 two not well resolved steps are observed, whereas 2 decomposes in one step. In the X-ray powder patterns of the grey products Sb2S3, Co/NiSbS and Co/NiS could be identified.

Cr (en)2SbS3:: the first example of a single SbS3 ligand in a transition-metal-complex, and the crystal structure of Cr (en)3SbS4

Abstract Application of mild solvothermal conditions in the reaction of CrCl3·8H2O, Sb2S3 and S in an aqueous solution of ethylenediamine (en) yielded the two novel thioantimonate compounds Cr (en)2SbS3 (1) and [Cr (en)3]SbS4 (2). The crystal structure of 1 consists of neutral chromium centered complexes, where chromium is chelated by two ethylendiamine molecules and one bidentate SbS 33− group giving a distorted octahedral coordination. Compound 1 is the first example of a transition metal complex with a SbS 33− ligand. Slightly different synthetic conditions lead to the formation of 2, which consists of isolated octahedral coordinated Cr (en)33 cations and tetrahedral SbS 43− anions. The crystal structures were determined and the thermal decomposition was investigated.

STRUCTURE AND THERMOCHEMICAL REACTIVITY OF CARUO3 AND SRRUO3

Abstract Single crystals of CaRuO3 (1) and SrRuO3 (2) have been synthesized by flux method and their structures have been determined by means of single crystal X-ray diffraction techniques. The crystallographic data are (1): formula weight fw = 189.15, orthorhombic, space group Pnma (No. 62), a = 5.524(1), b = 7.649(2), c = 5.354(1) A , V = 226.2 A 3 , Z = 4, Dx = 5.554 g cm−3, μ = 81.97 cm−1, final R = 0.031 for 297 observed reflections. (2): formula weight fw = 236.69, cubic, space group Pm 3 (No. 200), a = b = c =3.910(1) A , V = 59.8 A 3 , Z = 1, Dx = 6.572 g cm−3, μ = 275.28 cm−1, final R = 0.032 for 33 observed reflections. The thermochemical reactivity of the two phases has been investigated as function of temperature and ambient atmosphere. In oxidizing or inert gas atmospheres both compounds prove to be stable up to 1200 K. In reducing atmospheres such as molecular hydrogen, however, elementary ruthenium and the corresponding earth alkali metal oxides are obtained as microcrystalline mixtures at relatively low temperatures. The mechanisms of the reductions prove to be different.

Review. Synthesis of Inorganic-Organic Hybrid Thiometallate Materials with a Special Focus on Thioantimonates and Thiostannates and in situ X-Ray Scattering Studies of their Formation

A rich variety of inorganic-organic hybrid thioantimonates and thiostannates were prepared during the last few years under solvothermal conditions applying organic amine molecules or transition metal complexes as structure directors. In this review synthetic approaches to and structural features of these thiometallates are discussed. For thioantimonates(III) the structures range from well isolated thioanions to three-dimensional networks, whereas the structural chemistry of thiostannates(IV) is strongly dominated by the [Sn2S6]4− anion, and no three-dimensional thiostannate has been reported so far. In the structures of thioantimonates(III) several primary building units like the [SbS3] trigonal pyramid, the [SbS4] unit or even the [SbS5] moiety are joined by vertex- and/or edge-linkages to form building blocks of higher structural hierarchy like [Sb3S4] semi-cubes or SbxSx heterocycles. A pronounced difference between thioantimonate and thiostannate chemistry is the tendency of Sb(III) to enhance the coordination geometry via so-called secondary bonds. In most cases the environment of Sb(III) is better described as a 3+n polyhedron with n = 1 - 3. The thioantimonate(V) structural chemistry is less rich than that of thioantimonates(III), and the [SbS4]3− anion shows no tendency for further condensation. By applying suitable multidentate amine molecules, transition metal cations which normally prefer bonding to the N atoms of the amines can be incorporated into the thiometallate frameworks Graphical Abstract Review. Synthesis of Inorganic-Organic Hybrid Thiometallate Materials with a Special Focus on Thioantimonates and Thiostannates and in situ X-Ray Scattering Studies of their Formation

[V16Sb4O42(H2O){VO(C6H14N2)2}4]: a terminal expansion to a polyoxovanadate archetype.

The charge-neutral antimonatopolyoxovanadium(IV) cluster [V(IV)16Sb(III)4O42(H2O){V(IV)O(C6H14N2)2}4].10H2O.C6H14N2 was obtained under solvothermal conditions. The central cluster fragment, [V(IV) 16Sb(III)4O42], is a derivative of the [V18O42] archetype and is formed by replacing two VO5 polyhedra by two Sb2O5 units. The {V20Sb4} structure expands the {V16Sb4} motif by the addition of four square-pyramidal, terminal VO(1,2-diaminocyclohexane)2 groups. At low temperatures, the magnetic ground state is characterized by four independent S = 1/2 sites.

Organic Functionalization of Polyoxovanadates: SbN Bonds and Charge Control

Numerous approaches towards the utilization of polyoxometalates (POMs) require their direct covalent attachment to organic groups. This ranges from immobilization of POM catalysts on polymer matrices and integration of POMs into porous metal–organic frameworks (MOFs) to electrochromic hybrid systems. The synthesis strategies developed to date are predominantly not based on the formation of metal– organic bonds, but utilize other main-group elements as bonding mediators to link the organic functions to the POMs. These coupling reactions formally correspond to condensation of the POM cluster with alcohols or carboxylates (M O R), or amines (M=N R), but also with organodiazenido, organophosphato, organosilyl, or organotin groups. However, these strategies primarily target polyoxomolybdates and -tungstates. Various types of subsequent reactions of the organic functions attached to the POM (for example, 1,3dipolar cycloadditions (“click” chemistry), Sonogashira and Heck coupling reactions, or Diels–Alder reactions) emphasize the potential for the integration of such hybrid systems as building blocks into other structures. Polyoxovanadates, such as decavanadate, also exhibit interesting reactivities towards biomolecules, as exemplified by hydrolytic DNA cleavage, inhibition of oxygen consumption in membranes, or the inhibition of 6-phosphogluconate hydrogenase by tetravanadate. Organopolyoxovanadates, however, are relatively rare. Their synthesis usually is limited to a formal exchange of terminal oxido sites with alkoxides or phosphonates, the integration of which strongly affects, or directs, the resulting structure of the vanadate framework. Herein we present two examples that demonstrate how organic amines or ammonium groups can be added to existing polyoxovanadates through the formation of Sb N bonds, whereby the framework structure is retained and the negative charge on it can be largely or completely compensated, which can increase the solubility the polyoxovanadates in organic solvents. Our approach is based on the recently discovered class of antimonate polyoxovanadates, such as the spherical cluster anions [V16Sb4O42(H2O)] 8 , [V15Sb6O42(H2O)] 6 , and [V14Sb8O42(H2O)] 4 . Following systematic adjustments to the synthesis, which is strongly dependent on the pH value, we were able to isolate the organically functionalized analogues [V14Sb III 8(C6H15N3)4O42(H2O)]·4H2O (1) and (C6H17N3)2[V IV 15Sb III 6 (C6H15N3)2O42(H2O)]·2.5H2O (2), in which protonated amines bind to the spherical polyoxovanadate clusters through Sb N bonds. The structure of the two clusters in 1 and 2 can formally be derived from the archetypal spherical isopolyoxovanadate(IV) {V18O42} [11] by replacing four (in 1) or three (in 2) O4V= O square-based pyramids with an equal number of O2Sb(m-O)SbO2 groups (1: Sb-m-O: 1.930(6)–2.031(5) , 2 : Sb-mO: 1.930(5)–2.040(4) ). Abstraction of four VO5 pyramids in [V18O42] 12 results in the formation of two perpendicular, intersecting (O4V=O)8 rings of edge-sharing VO5 pyramids (Figure 1a). Both the geometric parameters of the Sb2O5 groups in 1 and 2 as well as the V-m-O (1.912(6)–1.981(6) ) and V-Oterminal (1.584(7)–1.637(6) ) bond lengths and V···V distances (2.818(2)–3.1011(19) ) are in line with other antimony polyoxovanadates.

Solvothermal Synthesis and Crystal Structure of the New Layered Thioantimonate(III) [Ni(C4H13N3)2]9Sb22S42 · 0.5H2O: Interconnection of the SbS3, SbS4, and SbS5 Primary Building Units Yielding the Very Large Sb30S30 Heteroring†

The novel thioantimonate(III) [Ni(dien)2]9Sb22S42 · 0.5H2O was synthesised under solvothermal conditions by reacting elemental Ni, Sb and S in an aqueous solution of diethylenetriamine (dien) (80%). The compound crystallises in the triclinic space group P1¯, a = 8.997(2) A, b = 15.293(3) A, c = 34.434(7) A, α = 85.51(3)°, β = 84.16(3)°, γ = 83.54(3)°, V = 4672.7 (16) A3, Z = 1. The layered [Sb22S4218—] anion in [Ni(dien)2]9Sb22S42 · 0.5H2O is composed of nine SbS3 trigonal pyramids, one SbS4 and one SbS5 unit. The interconnection of these units by sharing common S atoms yields Sb-S heterorings of different sizes. Besides the smaller Sb2S2 and Sb3S3 rings a very large Sb30S30 heteroring is observed. The structure directing effect of the [Ni(dien)2]2+ cations is obvious as they are located above and below the pores of the anion. The nine [Ni(dien)2]2+ cations exhibit different conformations. All Ni2+ cations are in an octahedral environment of six N atoms of two dien ligands. The anions and cations are stacked perpendicular to [100] in an alternating fashion. Solvothermale Synthese und Kristallstruktur des neuen schichtartigen Thioantimonats(III) [Ni(C4H13N3)2]9Sb22S42 · 0.5H2O: Verknupfung der primaren SbS3-, SbS4- und SbS5-Baueinheiten zu einem sehr grosen Sb30S30-Heteroring Das neue Thioantimonat(III) [Ni(dien)2]9Sb22S42 · 0.5H2O wurde unter solvothermalen Bedingungen aus elementarem Ni, Sb und S in einer 80%igen Diethylentriamin (dien) Losung hergestellt. Die Verbindung kristallisiert in der triklinen Raumgruppe P1¯ mit a = 8, 997(2) A, b = 15, 293(3) A, c = 34, 434(7) A, α = 85, 51(3)°, β = 84, 16(3)°, γ = 83, 54(3)°, V = 4672, 7 (16) A3, Z = 1. Das [Sb22S4218—] Anion in [Ni(dien)2]9Sb22S42 · 0.5H2O wird aus neun SbS3 trigonalen Pyramiden, einer SbS4- und einer SbS5-Einheit aufgebaut. Die Verknupfung dieser Einheiten uber gemeinsame Schwefelatome fuhrt zur Ausbildung von Sb-S-Heteroringen unterschiedlicher Grose. Neben Sb2S2- und Sb3S3-Ringen wird ein sehr groser Sb30S30-Heteroring gebildet. Der strukturdirigierende Effekt der Kationen wird dadurch deutlich, das sich die [Ni(dien)2]2+-Kationen ober- und unterhalb dieser Poren befinden. Die neun [Ni(dien)2]2+-Kationen liegen in verschiedenen Konformationen vor. Alle Ni2+-Kationen befinden sich in einer oktaedrischen Umgebung von sechs N-Atomen zweier dien-Liganden. Die Anionen und Kationen sind alternierend senkrecht zu [100] gestapelt.

The Layered Thiostannate (dienH2)Cu2Sn2S6: a Photoconductive Inorganic−Organic Hybrid Compound

The new inorganic-organic hybrid compound (dienH2)Cu2Sn2S6 (dien = diethylenetriamine) was synthesized under solvothermal conditions. It crystallizes in the tetragonal space group I4m2 with a = 7.8793(3) A, c = 24.9955(15) A, and V = 1551.80(13) A(3). The structure consists of anionic [Cu2Sn2S6](2-) layers extending in the (001) plane and protonated amine molecules as charge compensating ions sandwiched between the layers. The layered [Cu2Sn2S6](2-) anion is composed of a single layer of edge-sharing CuS4 tetrahedra which is joined above and below to straight chains constructed by corner-sharing SnS4 tetrahedra. The material is a semiconductor with an optical band gap of 1.51 eV. More interestingly, preliminary results demonstrate that the compound exhibits photoconductive properties with an increase of the conductivity by a factor of 3 when irradiated with UV light. Upon heating in an inert atmosphere the compound starts to decompose at about 256 degrees C.