Search

Mixing an aqueous solution of K8[Nb6O19]⋅16H2O with a DMSO/H2O solution of Cu(ClO4)2 · 6 H2O and cyclen at room temperature afforded crystallization of blue crystals of [(Cu(cyclen))6Nb6O19]⋅[ClO4]4·≈4H2O after slow evaporation of the solvents. The crystal structure contains the Lindqvist anion [Nb6O19]8– which is covalently expanded by six symmetry-related [Cu(cyclen)]2+ complexes via Nb-μ 2-O-Cu bridges yielding the positively charged [(Cu(cyclen))6Nb6O19]4+ cluster shell. The ClO4 − anions and crystal water molecules reside in the empty spaces of the packed clusters. The compound shows two electronic d-d transitions at energetic positions explaining the blue color.

Journal of solid state electrochemistry 26(11), 2501 - 2514 (2022). doi:10.1007/s10008-022-05246-3, We present new insights into the electrochemical properties of three metal sulfides MCr$_2$S$_4$ (M = Cr, Ti, Fe) probed as anode materials in sodium-ion batteries for the first time. The electrodes deliver decent reversible capacities and good long-term cycle stability, e.g., 470, 375, and 524 mAh g$^{−1}$ are obtained after 200 cycles applying 0.5 A g$^{−1}$ for M = Cr, Ti, and Fe, respectively. The reaction mechanisms are investigated via synchrotron-based X-ray powder diffraction and pair distribution function analyses. The highly crystalline educts are decomposed into Na$_2$S nanoparticles and ultra-small metal particles during initial discharge without formation of intermediate NaCrS$_2$ domains as previously reported for CuCrS$_2$ and NiCr$_2$S$_4$. After a full cycle, the structural integrity of MCr$_2$S$_4$ (M = Cr, Ti, Fe) is not recovered. Thus, the Na storage properties are attributed to redox reactions between nanoscopic to X-ray amorphous conversion products with only local atomic correlations M···S/S···S in the charged and M···M/Na···S in the discharged state., Published by Springer, New York

The synthesis, crystal structures and properties of two alkali metal 3-nitrohydrogenphthalates obtained by a 1:2 reaction of M2CO3 (M = K or Na) with 3-nitrophthalic acid (LH2) are reported. In the anhydrous potassium coordination polymer [K(LH)] (LH = 2-carboxy-3-nitrobenzoate) 1, the K+ cation is bonded to nine oxygen atoms from six symmetry related (LH)– ligands resulting in a distorted {KO9} coordination polyhedron. Five of the six oxygen atoms including a nitro oxygen atom of the crystallographically unique 2-carboxy-3-nitrobenzoate are involved in metal binding. The μ6-bridging mode of (LH)– places the K+ cations into the layers of the two-dimensional (2D) coordination polymer. Each {KO9} polyhedron in 1 shares edges with two other polyhedra along the b and c axes. A low temperature structure redetermination of [Na(L#H)(H2O)3]·H2O (L#H = 2-carboxy-6-nitrobenzoate) 2 has revealed that the (L#H)− anion is bonded to the Na+ cation in a monodentate fashion via the carbonyl oxygen atom of the –COOH group and two of the three unique aqua ligands exhibit a bridging bidentate mode stabilizing a chain polymer. The structure of compound 2 thus consists of chains of edge-sharing {NaO6} octahedra. Thermal decomposition of 1 or 2 results in the formation of metal carbonate residues.

The title compounds were prepared by precipitation from acidic solutions of the reactants in acetone/water. Bi(S2CNH2)2Cl (1) crystallizes in the non-centrosymmetric trigonal space group P32 with a = 8.6121(3) and c = 11.1554(4) Å, Z = 3; Bi(S2NH2)2SCN (2) in P21/c (monoclinic) with a = 5.5600(2), b = 14.3679(5), c = 12.8665(4) Å, and β = 90.37(3)°. In the crystal structure of 1 Bi3+ is in a sevenfold coordination of two bidentate and one monodentate S2CHNH2 − anions with an asymmetric coordination pattern of five Bi–S and two Bi–Cl− bonds. The linkage of these polyhedra via common Cl–S edges leads to a 1D polymeric structure with undulated chains propagating in the direction [001]. These chains are linked by strong and medium strong hydrogen bonds forming the 3D crystal structure. In the crystal structure of 2 the Bi3+ cation is in an eightfold coordination. The polyhedron can be described as a significantly distorted tetragonal anti-prism, capped by an additional S atom. Two of these prisms share a common quadrilateral face to form a “prism-double” (Bi2S10N2). These building units are linked by common edges, and the resulting 1D infinite angulated chains propagate along [100]. By contrast to organo-dithiocarbamate compounds, where C–H···X bridges are dominant, the interchain connections in the crystal structures of 1 and 2 are formed exclusively via N–H···S, N–H···Cl, and N–H···N interactions, generating the 3D networks. A significant eccentricity of the Bi3+ cation in the crystal structures of both complexes is observed. Both compounds emit light in the orange range of the electromagnetic spectrum.

The reaction of Na2MoO4·2H2O with 2-amino-2-(hydroxymethyl)propane-1,3-diol (LH) in water at room temperature results in the formation of the heterometallic coordination polymer [Mo2O6L2(Na2(H2O)4)]·2H2O 1 (L = 2-amino-3-hydroxy-2-(hydroxymethyl)propan-1-olato). The structure of 1 consists of a neutral (Mo2O6) unit located on an inversion center. The Mo atoms exhibit hexa-coordination and are bonded to two terminal and two bridging oxido ligands, an alkoxide oxygen and the amine N atoms of an anionic ligand L– resulting in the formation of an edge-sharing {Mo2O8N2} bioctahedron. The Na+ cations of a centrosymmetric bis(μ2-aqua)-bridged (Na2(H2O)4)2+ unit are penta-coordinated and bonded to two symmetry related L– ligands via the oxygen atoms of their OH groups. The µ3-bridging tetradentate binding mode of L– results in the formation of a two-dimensional heterometallic coordination polymer. The constituents of 1 viz. (Mo2O6), (L)–, (Na2(H2O)4)2+ and lattice water molecules are interlinked with the aid of three varieties of hydrogen bonding interactions. The corresponding tungstate reported recently has been obtained through a similar synthetic protocol and is isostructural.

Nanoscale 14(7), 2696 - 2710 (2022). doi:10.1039/D1NR06950K, Various electrode materials are considered for sodium-ion batteries (SIBs) and one important prerequisite for developments of SIBs is a detailed understanding about charge storage mechanisms. Herein, we present a rigorous study about Na storage properties of ultra-small Fe$_3$S$_4$ nanoparticles, synthesized applying a solvothermal route, which exhibit a very good electrochemical performance as anode material for SIBs. A closer look into electrochemical reaction pathways on the nanoscale, utilizing synchrotron-based X-ray diffraction and X-ray absorption techniques, reveals a complicated conversion mechanism. Initially, separation of Fe$_3$S$_4$ into nanocrystalline intermediates occurs accompanied by reduction of Fe$^{3+}$ to Fe$^{2+}$ cations. Discharge to 0.1 V leads to formation of strongly disordered Fe$^0$ finely dispersed in a nanosized Na$_2$S matrix. The resulting volume expansion leads to a worse long-term stability in the voltage range 3.0–0.1 V. Adjusting the lower cut-off potential to 0.5 V, crystallization of Na$_2$S is prevented and a completely amorphous intermediate stage is formed. Thus, the smaller voltage window is favorable for long-term stability, yielding highly reversible capacity retention, e.g., 486 mAh g$^{−1}$ after 300 cycles applying 0.5 A g$^{−1}$ and superior coulombic efficiencies >99.9%. During charge to 3.0 V, Fe$_3$S$_4$ with smaller domains are reversibly generated in the 1st cycle, but further cycling results in loss of structural long-range order, whereas the local environment resembles that of Fe$_3$S$_4$ in subsequent charged states. Electrokinetic analyses reveal high capacitive contributions to the charge storage, indicating shortened diffusion lengths and thus, redox reactions occur predominantly at surfaces of nanosized conversion products., Published by RSC Publ., Cambridge

Bulk isocubanite (CuFe2S3) was synthesized via a multistep high-temperature synthesis and was investigated as an anode material for sodium-ion batteries. CuFe2S3 exhibits an excellent electrochemical performance with a capacity retention of 422 mA h g-1 for more than 1000 cycles at a current rate of 0.5 A g-1 (0.85 C). The complex reaction mechanism of the first cycle was investigated via PXRD and X-ray absorption spectroscopy. At the early stages of Na uptake, CuFe2S3 is converted to form crystalline CuFeS2 and nanocrystalline NaFe1.5S2 simultaneously. By increasing the Na content, Cu+ is reduced to nanocrystalline Cu, followed by the reduction of Fe2+ to amorphous Fe0 while reflections of nanocrystalline Na2S appear. During charging up to -5 Na/f.u., the intermediate NaFe1.5S2 appears again, which transforms in the last step of charging to a new unknown phase. This unknown phase together with NaFe1.5S2 plays a key role in the mechanism for the following cycles, evidenced by the PXRD investigation of the second cycle. Even after 400 cycles, the occurrence of nanocrystalline phases made it possible to gain insights into the alteration of the mechanism, which shows that CuxS phases play an important role in the region of constant specific capacity.

Diffusion-based room temperature syntheses using K8{Ta6O19}·16H2O, d-block metal (M) salts (M = Cu, Zn, or Cd), and the macrocyclic ligand 1,4,8,11-tetraazacyclotetradecane (cyclam) led to crystall...

Electrochemical performance of the layered compound CrPS4 for the usage as anode material in sodium-ion batteries (SIBs) was examined and exceptional reversible long-term capacity and capacity rete...

The new compound K2[Ni(dien)2]{[Ni(dien)]2Ta6O19}·11 H2O crystallized at room temperature applying a diffusion based reaction in a H2O/DMSO mixture using K8{Ta6O19}·16 H2O, Ni(NO3)2·6H2O and dien (diethylenetriamine). In the crystal structure, the Lindqvist-type anion [Ta6O19]8– is structurally expanded by two octahedrally Ni2+-centered complexes via three Ni–µ 2-O–Ta bonds thus generating the new {[Ni(dien)]2Ta6O19}4– anion. Two KO8 polyhedra share a common edge to form a K2O14 moiety, which connects the {[Ni(dien)]2Ta6O19}4– cluster shells into chains. The isolated [Ni(dien)2]2+ complexes are located in voids generated by the structural arrangement of the chains. An extended hydrogen bonding network between the different constituents generates a 3D network. The crystal water molecules can be thermally removed to form a highly crystalline dehydrated compound. Partial water uptake leads to the formation of a crystalline intermediate with a reduced unit cell volume compared to the fully hydrated sample. Water sorption experiments demonstrate that the fully dehydrated sample can be fully reconverted to the hydrated compound. The crystal field splitting parameters for the octahedrally coordinated Ni2+-centered complexes have been evaluated from an UV/Vis spectrum yielding D q = 1056 cm−1 and B = 887 cm−1.

The reaction of the water-rich compound [Sr(H2O)7(4-nba)](4-nba)·2H2O (4-nba = 4-nitrobenzoate) with dimethylformamide (DMF) or N-methylformamide (NMF) or pyrazole (Pyr) resulted in the incorporation of the O- or N-donor ligand in the coordination sphere of Sr(II) forming the one-dimensional (1D) coordination polymers [Sr(H2O)3(DMF)(4-nba)](4-nba) (1), [Sr2(H2O)2(NMF)3(4-nba)4] (2) and [Sr(Pyr)2(4-nba)2] (3) respectively. In the case of Mg(II), a similar protocol afforded crystallization of [Mg(H2O)6](4-nba)2(DMF)2 (4), [Mg(H2O)6](3-nba)2(Acet)2 (5), (3-nba = 3-nitrobenzoate; Acet = Acetamide) in which the amides function as solvates. The syntheses, crystal structures and properties of 1–5 are reported. In 1–3 Sr(II) exhibits eight coordination while Mg(II) displays hexa coordination in 4 and 5 forming the centrosymmetric octahedral [Mg(H2O)6]2+ unit. The µ3-η2:η2-tetradentate bridging binding modes in 1 and 2 and µ2-η1:η2-tridentate bridging binding mode in 3 of the 4-nitrobenzoate result in the formation of 1D coordination polymer. The carboxylate ion does not coordinate to Mg(II) in 4 and 5, but functions as a charge balancing counter anion. The {SrO8} polyhedra in 1 and {SrN2O6} polyhedra in 3 share edges in the 1D chains, while in 2 the {SrO8} polyhedra are linked into a 1D chain via alternate edge and face sharing arrangement. Compounds 1 (C–H···O, O–H···O) and 3 (C–H···O, N–H···O) exhibit two varieties of hydrogen bonding interactions while 2 and 5 are involved in three types of H-bonding interactions viz. C–H···O, O–H···O, N–H···O. A study of the structural features of several alkaline-earth 4-nitrobenzoates is described.

An attempted isolation of the elusive diammonium tetraoxidotungstate (NH4)2[WO4] as its imidazole (Im) adduct resulted in the serendipitous formation of hepta(ammonium) penta(1H-imidazol-3-ium) par...

Highly crystalline CuFeS2 containing earth-abundant and environmentally friendly elements prepared via a high-temperature synthesis exhibits an excellent electrochemical performance as an anode material in sodium-ion batteries. The initial specific capacity of 460 mAh g-1 increases to 512 mAh g-1 in the 150th cycle and then decreases to a still very high value of 444 mAh g-1 at 0.5 A g-1 in the remaining 550 cycles. Even for a large current density, a pronounced cycling stability is observed. Here, we demonstrate that combining the results of X-ray powder diffraction experiments, pair distribution function analysis, and 23Na NMR and Mossbauer spectroscopy investigations performed at different stages of discharging and charging processes allows elucidation of very complex reaction mechanisms. In the first step after uptake of 1 Na/CuFeS2, nanocrystalline NaCuFeS2 is formed as an intermediate phase, which surprisingly could be recovered during charging. On increasing the Na content, Cu+ is reduced to nanocrystalline Cu, while nanocrystalline Na2S and nanosized elemental Fe are formed in the discharged state. After charging, the main crystalline phase is NaCuFeS2. At the 150th cycle, the mechanisms clearly changed, and in the charged state, nanocrystalline CuxS phases are observed. At later stages of cycling, the mechanisms are altered again: NaF, Cu2S, and Cu7.2S4 appeared in the discharged state, while NaF and Cu5FeS4 are observed in the charged state. In contrast to a typical conversion reaction, nanocrystalline phases play the dominant role, which are responsible for the high reversible capacity and long-term stability.

The new coordination polymer Cr(en)2As2VO7 (en=ethylenediamine) was synthesized under solvothermal conditions as deep red crystals. In the crystal structure VO4 tetrahedra and As2O5 handles formed by corner-sharing of two AsO3 pyramidal units are joined by common oxygen atoms into an undulated chain that is directed along the crystallographic b-axis. The chain is decorated by [Cr(en)2]3+ complexes with the Cr3+ cation having bonds to two terminal O2− anions of the As2O5 moiety thus generating a CrN4O2 octahedron, which displays a cis-configuration. The connection mode between Cr3+ and As2O5 leads to formation of a six-membered CrAs2O3 ring. The chains are arranged in a layer-like fashion in the (001) plane and these layers are stacked along [001]. A large number of N−H⋅⋅⋅O and C−H⋅⋅⋅O hydrogen bonds generate a three dimensional network. A Hirshfeld surface analysis was performed for visualizing the extended interchain interactions. The hydrogen bonding interactions are clearly detected in the IR spectrum. The UV-Vis spectrum shows an absorption at 2.3 eV which is in agreement with the red color of the sample.

[VIV30SbIII8O78]12−, currently the largest known antimonato-polyoxovanadate (Sb-POV), features three perpendicular, intersecting 12-membered rings of edge-sharing O4VO square pyramids. While in two rings the apices of all O4VO 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.

Liquid crystalline materials found numerous applications in modern technologies due to their ability to respond to external fields. In this context, ferronematic liquid crystals are fascinating because they offer a response to weak magnetic fields in addition to electrical fields. Nevertheless, the synthesis of stable ferronematic liquid crystals represents a challenge for colloidal and synthetic chemists. In this work, we present a straight-forward strategy for directly incorporating presynthesized magnetic nanoparticles into every other interlayer of synthetic 2 : 1 layered silicates, which subsequently can be swollen to nematic phases simply by immersion into water, offering almost infinite stability. The resulting ferronematic suspension shows a sensitive response to magnetic fields. Moreover, the synthetic strategy is highly modular, enabling for variations of the magnetic nanosheets that allow for tuning the interaction between nanosheets and blocking temperature.

The new compound {[Cu(phen)]2[Cu(phen)2]2Nb6O19}·24H2O (I) (phen = 1,10-phenanthroline) was prepared under ambient conditions. The crystal structure is composed of the [Nb6O19]6– anion which is exp...

Herein, we present an extensive study of the magnetic and magnetotransport properties of iron-inserted transition-metal dichalcogenide Fe1/3TaS2. High-quality single crystals were prepared by an im...