Room-Temperature Solid-State Transformation of Na4 SnS4 ⋠14H2 O into Na4 Sn2 S6 ⋠5H2 O: An Unusual Epitaxial Reaction Including Bond Formation, Mass Transport, and Ionic Conductivity.

A highly unusual solid-state epitaxy-induced phase transformation of Na4 SnS4 ⋅ 14H2 O (I) into Na4 Sn2 S6 ⋅ 5H2 O (II) occurs at room temperature. Ab initio molecular dynamics (AIMD) simulations indicate an internal acid-base reaction to form [SnS3 SH]3- which condensates to [Sn2 S6 ]4- . The reaction involves a complex sequence of O-H bond cleavage, S2- protonation, Sn-S bond formation and diffusion of various species while preserving the crystal morphology. In situ Raman and IR spectroscopy evidence the formation of [Sn2 S6 ]4- . DFT calculations allowed assignment of all bands appearing during the transformation. X-ray diffraction and in situ 1 H NMR demonstrate a transformation within several days and yield a reaction turnover of ≈0.38 %/h. AIMD and experimental ionic conductivity data closely follow a Vogel-Fulcher-Tammann type T dependence with D(Na)=6×10-14  m2 s-1 at T=300 K with values increasing by three orders of magnitude from -20 to +25 °C.

Directed Dehydration as Synthetic Tool for Generation of a New Na4 SnS4 Polymorph: Crystal Structure, Na+ Conductivity, and Influence of Sb-Substitution.

We present the convenient synthesis and characterization of the new ternary thiostannate Na4 SnS4 (space group I 4 1 / a c d ) by directed removal of crystal water molecules from Na4 SnS4 ⋅14 H2 O. The compound represents a new kinetically stable polymorph of Na4 SnS4 , which is transformed into the known, thermodynamically stable form (space group P 4 ‾ 2 1 c ) at elevated temperatures. Thermal co-decomposition of mixtures with Na3 SbS4 ⋅9 H2 O generates solid solution products Na4-x Sn1-x Sbx S4 (x=0.01, 0.10) isostructural to the new polymorph (x=0). Incorporation of Sb5+ affects the bonding and local structural situation noticeably evidenced by X-ray diffraction, 119 Sn and 23 Na NMR, and 119 Sn Mössbauer spectroscopy. Electrochemical impedance spectroscopy demonstrates an enormous improvement of the ionic conductivity with increasing Sb content for the solid solution (σ25°C =2×10-3 , 2×10-2 , and 0.1 mS cm-1 for x=0, 0.01, and 0.10), being several orders of magnitude higher than for the known Na4 SnS4 polymorph.

Three intersecting {V12} rings: {V30Sb8}, an ultra-large polyoxovanadate cluster shell.

[VIV30SbIII8O78]12-, currently the largest known antimonato-polyoxovanadate (Sb-POV), features three perpendicular, intersecting 12-membered rings of edge-sharing O4V[double bond, length as m-dash]O square pyramids. While in two rings the apices of all O4V[double bond, length as m-dash]O pyramids point outwards, four apices of the third ring are directed into the cavity of the cluster shell, a concave structural motif not previously observed in polyoxovanadate chemistry. SbIII centers cap the eight niches defined by the octands of the {V30O78} cluster shell, resulting in discrete trigonal pyramidal SbO3 units, a second unprecedented feature. Within the resulting spin topology with numerous local geometrically frustrated motifs, the 30 spin-1/2 sites couple antiferromagnetically via a complex set of exchange pathways.

Two Pseudopolymorphic Star-Shaped Tetranuclear Co(3+) Compounds with Disulfide Anions Exhibiting Two Different Connection Modes and Promising Photocatalytic Properties.

The compound [Co4(C6H14N2)4(µ4-S2)2(µ2-S2)4] (I) and the pseudo-polymorph [Co4(C6H14N2)4(µ4-S2)2(µ2-S2)4]⋅4 H2O (II) were obtained under solvothermal conditions (C6H14N2=trans-1,2-diaminocyclohexane). The structures feature S2(2-) ions exhibiting two different coordination modes. Terminal S2(2-) entities join two Co(3+) centres in a µ2 fashion, whereas the central S2(2-) groups connect four Co(3+) cations in a µ4-coordination mode. Compound II can be transformed into compound I by heat and storage over P2O5 and storing compound I in humid air yields in the formation of compound II. The intermolecular interactions investigated through Hirshfeld surface analysis reveal that besides S⋅⋅⋅H bonding close contacts are associated with relatively weak H⋅⋅⋅H interactions. A detailed DFT analysis of the bonding situation explains the long S-S bonds in the µ4-bridging S2(2-) units and the short bonds for the S2(2-) moieties in the µ2-connecting mode. Photocatalytic hydrogen evolution experiments demonstrate the potential of compound II as catalyst.

Unprecedented layered inorganic-organic hybrid compound Mn(3)Sb(2)S(6)(C(6)H(18)N(4)) composed of Mn(4)Sb(2)S(6) double-cubane units showing magnetic long-range order and frustration.

The title compound Mn(3)Sb(2)S(6)(C(6)H(18)N(4)) (C(6)H(18)N(4) = triethylenetetramine) was obtained under solvothermal conditions by reacting Mn, Sb, S, and the amine at 140 degrees C for 7 days. The compound crystallizes in the triclinic space group P1 with a = 6.645(1) A, b = 8.667(1) A, c = 9.660(1) A, alpha = 90.82(2) degrees , beta = 109.70(2) degrees , gamma = 110.68(2) degrees , Z = 1, and V = 484.4(1) A(3). The Mn(4)Sb(2)S(6) double-heterocubane unit is the main motif in the structure of the title compound, which results from the interconnection of two SbS(3) trigonal pyramids, two MnS(6) octahedra, and two MnS(4)N(2) octahedra. The two N atoms completing the environment of the latter Mn(2+) ions belong to the tetradentate amine; i.e., the amine acts in a bidentate manner. The Mn(4)Sb(2)S(6) groups are joined by corner sharing of the MnS(6) octahedra, yielding one-dimensional linear Mn(3)Sb(2)S(6) rods along [100]. The two other N atoms of the amine molecule act in a bidentate manner to Mn(2+) ions of neighboring rods, thus producing layers within the (010) plane. Within the rods, the arrangement of the Mn(2+) ions in triangles leads to a chain of Mn(2+) diamonds connected via opposite corners. For the magnetic properties, each edge connecting the Mn(2+) ions represents a superexchange path due to coupling of the Mn(2+) centers via S bridges. The resulting Mn(2+) triangles give rise to substantial competing interaction and magnetic frustration. Below about 100 K, a gradual buildup of short-range antiferromagnetic correlations is observed. At lower temperatures, long-range antiferromagnetic interactions occur with T(N) = 2.90 K, as indicated by a lambda-type anomaly in the heat capacity curve. The analysis of the magnetic and heat capacity data evidences that the magnetic properties are essentially determined by the one-dimensional character of the Mn(3)Sb(2)S(6) chain. In addition, significant magnetic frustration due to the arrangement of the Mn(2+) ions in a triangular configuration cannot be neglected.