Directed Transformation of Molecules to Solids: Synthesis of a Microporous Sulfide from Molecular Germanium Sulfide Cages

Electroreduction-Driven Formation and Connectivity of Polyoxometalate Coordination Networks

We present the synthesis of metal oxide coordination networks based on Preyssler-type polyoxoanions ([NaP5W30O110]14- and [NaP5MoW29O110]14-) bridged with metal-aquo complexes ([M(H2O)n]m+, Mm+ = Co2+, Ni2+, Zn2+, Y3+), induced by electrochemical reduction. Networks bridged with first-row transition metals are isostructural with a previously reported Co-bridged structure, while the Y3+-bridged structure is new. All networks feature an uncommon binding motif of the metal cation to the oxygen atoms at cap positions, which we hypothesize is due to increased electron density at the cap upon reduction. Oxidation of a Zn2+-bridged network resulted in a new structure in which Zn2+-Ocap bonds are lost, indicating the importance of reduction in the connectivity of these polyoxometalate-based coordination networks.

Adamantane-type clusters: compounds with a ubiquitous architecture but a wide variety of compositions and unexpected materials properties

The research into adamantane-type compounds has gained momentum in recent years, yielding remarkable new applications for this class of materials. In particular, organic adamantane derivatives (AdR4) or inorganic adamantane-type compounds of the general formula [(RT)4E6] (R: organic substituent; T: group 14 atom C, Si, Ge, Sn; E: chalcogenide atom S, Se, Te, or CH2) were shown to exhibit strong nonlinear optical (NLO) properties, either second-harmonic generation (SHG) or an unprecedented type of highly-directed white-light generation (WLG) - depending on their respective crystalline or amorphous nature. The (missing) crystallinity, as well as the maximum wavelengths of the optical transitions, are controlled by the clusters' elemental composition and by the nature of the organic groups R. Very recently, it has been additionally shown that cluster cores with increased inhomogeneity, like the one in compounds [RSi{CH2Sn(E)R'}3], not only affect the chemical properties, such as increased robustness and reversible melting behaviour, but that such 'cluster glasses' form a conceptually new basis for their use in light conversion devices. These findings are likely only the tip of the iceberg, as beside elemental combinations including group 14 and group 16 elements, many more adamantane-type clusters (on the one hand) and related architectures representing extensions of adamantane-type clusters (on the other hand) are known, but have not yet been addressed in terms of their opto-electronic properties. In this review, we therefore present a survey of all known classes of adanmantane-type compounds and their respective synthetic access as well as their optical properties, if reported.

(C6H15N3)1.3(NH4)1.5H1.5In3SnS8: a layered metal sulfide based on supertetrahedral T2 clusters with photoelectric response and ion exchange properties

A new layered metal sulfide, namely (C6H15N3)1.3(NH4)1.5H1.5In3SnS8 (1, C6H15N3 = N-(2-aminoethyl) piperazine), has been solvothermally synthesized and characterized. Compound 1 crystallizes in the monoclinic space group C2/c. Its structure features a two-dimensional layer of {In3SnS8}n3n- with the (4,4) topology net, which is formed by interlinking supertetrahedral T2 clusters as secondary building units. Band structure calculations revealed that 1 had a band gap of 2.7 eV. The photoelectric response of 1 showed steady and reversible on/off cycles with an "on" state of 121.13 nA cm-2. Moreover, the activation of 1 by replacing the sluggish organic cations with harder K+ ions endowed the material with improved adsorption performances for Sr2+ ions from aqueous solutions.

Layered 3D Covalent Organic Framework Films Based on Carbon-Carbon Bonds

The development of covalent organic frameworks (COFs) during the past decades has led to a variety of promising applications within gas storage, catalysis, drug delivery, and sensing. Even though most described synthesis methods result in powdery COFs with uncontrolled grain size, several approaches to grow COF films have recently been explored. However, in all COFs so far presented, the isolated materials are chemically homogeneous, with all functionalities homogeneously distributed throughout the entire material. Strategies to synthetically manipulate the spatial distribution of functionalities in a single film would be game changing. Specifically, this would allow for the introduction of local functionalities and even consecutive functions in single frameworks, thus broadening their synthetic versatility and application potential. Here, we synthesize two 3D crystalline COF films. The frameworks, the ionic B-based and neutral C-based COFs, have similar unit cell parameters, which enables their epitaxial stacking in a layered 3D COF film. The film growth was monitored in real time using a quartz crystal microbalance, showing linear growth with respect to reaction time. The high degree of polymerization was confirmed by chemical analysis and vibrational spectroscopy. Their polycrystalline and anisotropic natures were confirmed with grazing incidence X-ray diffraction. We further expand the scope of the concept by making layered films from COF-300 and its iodinated derivative. Finally, the work presented here will pave the path for multifunctional COF films where concurrent functionalities are embedded in the same crystalline material.

Open-framework hybrid zinc/tin selenide as an ultrafast adsorbent for Cs+, Ba2+, Co2+, and Ni2

Efficient adsorption of radioactive ¹³⁷Cs⁺ and ⁶⁰Co²⁺ and their decay products ¹³⁷Ba²⁺ and ⁶⁰Ni²⁺ bears significance for hazard elimination in case of nuclear emergency, which relies on the adsorption rate enhancement that takes advantages of compositional and structural optimization. Herein, we report a zinc-doped selenidostannate constructed from T2-supertetrahedral clusters, namely K_3.4(CH₃NH₃)_0.45(NH₄)_0.15Zn₂Sn₃Se₁₀·3.4 H₂O (ZnSnSe-1K). The soft Se and micro-porosity synergistically endow this material with a binding affinity to Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺ ions and ultrafast kinetics with R > 97.6% in 2-60 min. In particular, ZnSnSe-1K can remove 99.34% of Cs⁺ in 2 min ⁽K_d^Cs > 1.5 × 10⁵ mL g^-1), contributing to a record rate constant k₂ of 9.240 g mg^-1 min^-1 that surpasses all metal chalcogenide adsorbents. ZnSnSe-1K exhibits good acid/base tolerance (pH = 0-12), and the adsorption capacities at neutral are 253.61 ± 9.15, 108.94 ± 25.32, 45.76 ± 14.19 and 38.49 ± 2.99 mg g^-1 for Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺, respectively. The adsorption performances resist well co-existing cations and anions, and the removal rates can keep above or close to 90% even in sea water. ZnSnSe-1K is employed in continuous column and membrane filtration, both of which shows excellent elimination efficiency (R > 99%) for mixed Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺. Especially, the membrane with an ultrathin (70 µm) ZnSnSe-1K layer can remove 97-100% Cs⁺ in suction filtration with a short contact time of 0.33 s. Combined with the simple synthesis, facile elution and great irradiation resistance, ZnSnSe-1K emerges as a selenide adsorbent candidate for use in environmental remediation especially that involving nuclear waste disposal.

Solvent-controlled ion-coupled charge transport in microporous metal chalcogenides

Interactions between ions and itinerant charges govern electronic processes ranging from the redox chemistry of molecules to the conductivity of organic semiconductors, but remain an open frontier in the study of microporous materials. These interactions may strongly influence the electronic behavior of microporous materials that confine ions and charges to length scales comparable to proton-coupled electron transfer. Yet despite mounting evidence that both solvent and electrolyte influence charge transport through ion-charge interactions in metal-organic frameworks, fundamental microscopic insights are only just beginning to emerge. Here, through electrochemical analysis of two open-framework chalcogenides TMA2FeGe4S10 and TMA2ZnGe4S10, we outline the key signatures of ion-coupled charge transport in band-type and hopping-type microporous conductors. Pressed-pellet direct-current and impedance techniques reveal that solvent enhances the conductivity of both materials, but for distinct mechanistic reasons. This analysis required the development of a fitting method that provides a novel quantitative metric of concerted ion-charge motion. Taken together, these results provide chemical parameters for a general understanding of electrochemistry in nanoconfined spaces and for designing microporous conductors and electrochemical methods used to evaluate them.

PEG-Infiltrated Polyoxometalate Frameworks with Flexible Form-Factors

We present the synthesis of metal oxide frameworks composed of the Preyssler anion, [NaP₅W₃₀O₁₁₀]^14-, bridged with transition-metal cations and infiltrated with polyethylene glycol. The frameworks can be dissolved in water to form freestanding rigid or flexible films or gels. Powder X-ray diffraction shows that all form-factors maintain the short-range order of the original crystals. Raman spectroscopy reveals that, similar to hydrogels, the macroscopic mechanical properties of these composites are dependent on the water content and the extent of hydrogen-bonding within the water network. The understanding gained from these studies facilitates solution-phase processing of polyoxometalate frameworks into flexible form factors.

Two new metal-chalcogenide-cluster-based frameworks with single metal ions of Zn2+(/Sb3+) serving as inter-cluster linkers

Two new metal-chalcogenide-cluster-based frameworks, in which P1-ZnSnS clusters are linked to each other by both corner-shared S^2- ions and single metal ions of Zn²⁺ (or Sb³⁺) to form one new 3D (3,4)-connected network (MCCF-22) and one 2D-layered framework (MCCF-23), respectively, are reported. Notably, MCCF-22 exhibits good performance toward photodegradation of methylene blue compared with its analogue framework with only S^2- ions as the linker.

Atomically precise metal chalcogenide supertetrahedral clusters: frameworks to molecules, and structure to function

Metal chalcogenide supertetrahedral clusters (MCSCs) are of significance for developing crystalline porous framework materials and atomically precise cluster chemistry. Early research interest focused on the synthetic and structural chemistry of MCSC-based porous semiconductor materials with different cluster sizes/compositions and their applications in adsorption-based separation and optoelectronics. More recently, focus has shifted to the cluster chemistry of MCSCs to establish atomically precise structure-composition-property relationships, which are critical for regulating the properties and expanding the applications of MCSCs. Importantly, MCSCs are similar to II-VI or I-III-VI semiconductor nanocrystals (also called quantum dots, QDs) but avoid their inherent size polydispersity and structural ambiguity. Thus, discrete MCSCs, especially those that are solution-processable, could provide models for understanding various issues that cannot be easily clarified using QDs. This review covers three decades of efforts on MCSCs, including advancements in MCSC-based open frameworks (reticular chemistry), the precise structure-property relationships of MCSCs (cluster chemistry), and the functionalization and applications of MCSC-based microcrystals. An outlook on remaining problems to be solved and future trends is also presented.

Consolidation of 2D Frameworks Based on Corner-Shared Supertetrahedral T5 Clusters via M2OS2 Units for Tunable Photoluminescent and Semiconductor Properties

Introducing transition metals into the intercluster linkers has been considered an important strategy for the rapid development of metal chalcogenide supertetrahedral (Tn) cluster-based open frameworks with excellent properties. However, using this strategy for achieving the structure and property tunability in the cluster-based framework of Tn (n ≥ 5) is still a great challenge. Herein, we report on three new sulfide and oxosulfide open frameworks of T5 clusters, i.e., T5-ZnMnInOS ([In₃₀Zn₅Mn₄O₂S₅₈]^12-), T5-MnInOS ([In₃₄Mn₅O₂S₅₈]^8-), and T5-MnInS ([In₂₈Mn₆S₅₄]^12-). Interestingly, transition metals Zn and Mn are successfully introduced into T5-ZnMnInOS and T5-MnInOS via the consolidation of corner-shared Zn₂OS₂ and Mn₂OS₂ units, respectively. Under the photoexcitation of UV light, three compounds can emit bright-orange-red light closely associated with the Mn²⁺ ions, and the compounds containing M₂OS₂ units exhibit better photoluminescence (PL) lifetimes. Variable-temperature PL spectra demonstrate that the introduced M₂OS₂ units are favorable for weakening the deformation of the skeleton structure and decreasing the red shifts of the emission peaks at low temperatures. Moreover, the experimental results exhibit that the three compounds are wide-band-gap semiconductors and that the photogenerated electron separation efficiency can be doubly increased because the intercluster linkers are fixed by the M₂OS₂ units. This work paves a new way for enriching the content and distribution types of transition-metal sites in the supertetrahedral cluster-based metal chalcogenide open frameworks.

A chalcogenide-cluster-based semiconducting nanotube array with oriented photoconductive behavior

The interesting physical and chemical properties of carbon nanotubes (CNTs) have prompted the search for diverse inorganic nanotubes with different compositions to expand the number of available nanotechnology applications. Among these materials, crystalline inorganic nanotubes with well-defined structures and uniform sizes are suitable for understanding structure-activity relationships. However, their preparation comes with large synthetic challenges owing to their inherent complexity. Herein, we report the example of a crystalline nanotube array based on a supertetrahedral chalcogenide cluster, K₃[K(Cu₂Ge₃Se₉)(H₂O)] (1). To the best of our knowledge, this nanotube array possesses the largest diameter of crystalline inorganic nanotubes reported to date and exhibits an excellent structure-dependent electric conductivity and an oriented photoconductive behavior. This work represents a significant breakthrough both in terms of the structure of cluster-based metal chalcogenides and in the conductivity of crystalline nanotube arrays (i.e., an enhancement of ~4 orders of magnitude).

Different Chemical Environments of [Ge4Se10]4- in the Li+ Compounds [Li4(H2O)16][Ge4Se10]·4.33H2O, [{Li4(thf)12}Ge4Se10], and [Li2(H2O)8][MnGe4Se10], and Ionic Conductivity of Underlying "Li4Ge4Se10"

The crystalline selenido germanates [Li₄(H₂O)₁₆][Ge₄Se₁₀]·4.3H₂O (1), [{Li₄(thf)₁₂}Ge₄Se₁₀] (2), and [Li₂(H₂O)₈][MnGe₄Se₁₀] (3) (thf = THF = tetrahydrofuran) were obtained by an extraction of a glassy ternary phase of the nominal composition Li₄Ge₄Se₁₀ (=Li₂S·2GeSe₂) with water (1) or THF (2) and slow evaporation of the solvent or by being layered with MnBr₂ in H₂O/MeOH (3), respectively. The compounds contain known selenido germanate anions, however, for the first time with Li⁺ counterions. This is especially remarkable for the prominent _∞³{[MnGe₄Se₁₀]^2-} open-framework structure, which was reported to crystallize with (NMe₄)⁺, Cs⁺, Rb⁺, and K⁺ counterions, but it has not yet been realized with the smallest alkali metal cation. Impedance spectroscopic studies on Li₄Ge₄Se₁₀ classify the glassy solid as a moderate Li⁺ ion conductor.

A quasi-D3-symmetrical metal chalcogenide cluster constructed by the corner-sharing of two T3 supertetrahedra

The third type of a discrete cluster of metal chalcogenide was successfully prepared by selecting the organic base with strong alkaline and weak solvation. This work further enriches the structure chemistry of discrete supertetrahedral clusters.

Stepwise Conversion from GeO2 to [MGe4S10]n3n- (M = Cu, Ag) Polymer via Isolatable [Ge2S6]4- and [Ge4S10]4- Anions by Virtue of Templating Technique

Rational synthesis of inorganic matter remains a great challenge encountered with modern synthetic chemistry. Here we reported the stepwise solvothermal conversion from GeO₂ to [MGe₄S₁₀]_n^3n- (M = Cu, Ag) polymer via isolatable [Ge₂S₆]^4- and [Ge₄S₁₀]^4- anions by virtue of templating technique. The facile sulfuration of GeO₂ resulted in the methylammonium-templated dimeric thiogermanate [CH₃NH₃]₄Ge₂S₆ (1). This was used subsequently as a precursor for the formation of adamantane-like [Ge₄S₁₀]^4- cluster, which was isolated as a mixed methylammonium/ethylammonium salt [CH₃CH₂NH₃]₃[CH₃NH₃]Ge₄S₁₀ (2). Compound 2 was then successfully used as a precursor to react with Cu⁺ and Ag⁺ cations in the presence of tetraethylammonium, resulting in alternating copolymeric products [(CH₃CH₂)₄N]₃MGe₄S₁₀ (M = Cu (3), Ag (4)), whose anionic moieties feature a novel zigzag chainlike structure constructed by [Ge₄S₁₀]^4- clusters via two-coordinate Cu⁺/Ag⁺ linkers. Mixed amine/ethanol or deep eutectic solvents were applied as media for the syntheses of 1-4, and all the products were characterized in the solid state and solution. Crystal structural analysis of the title compounds revealed significant templating roles of the alkylammonium cations as both space-filling agents and hydrogen-bonding donors, suggesting the structure-directing mechanism for the species formation and crystal growth. The design and optimization of multistep structural conversion upon templating effects would be beneficial for drawing rational, predictable pathways for inorganic synthesis.

A wide pH-range stable crystalline framework based on the largest tin-oxysulfide cluster [Sn20O10S34]

We report, herein, a diamond-like oxysulfide framework, 3D-T4-SnOS, based on the largest supertetrahedral cluster of Sn⁴⁺ ions, i.e. [Sn₂₀O₁₀S₃₄]. The framework remains intact in aqueous solution over a pH range between 1 and 14, and has a narrower optical bandgap, red-shifted fluorescence emission, and an enhanced photoelectric response compared to that of the smaller version, 2D-T3-SnOS, which has a building unit of supertetrahedral [Sn₁₀O₄S₂₀].

A series of new hybrid chalcogenogermanates: the rare examples of chalcogenogermanates combined with trivalent vanadium complexes

A series of new hybrid chalcogenogermanates [Mn₂(en)₄Ge₂S₆]_n (1, en = ethylenediamine), [Mn₂(dap)₄Ge₂S₆]_n (2, dap = 1,2-diaminopropane), [H₂dien]_n[MnGeS₄]_n (3, dien = diethylenetriamine), [V(en)₂(ea)]₂[Ge₂Se₆] (4, Hea = ethanolamine), [V(teta)(ea)]₂[Ge₂Se₆] (5, teta = triethylenetetramine) and [V₂(en)₆(μ-O)][Ge₂Se₆] (6) were solvothermally synthesized and structurally characterized. Both 1 and 2 contain dimeric [Ge₂S₆]^4- anions and [Mn(en)₂]²⁺/[Mn(dap)₂]²⁺ complex cations, which are interconnected to generate 1-D neutral chain-like structures [Mn₂(en)₄Ge₂S₆]_n and [Mn₂(dap)₄Ge₂S₆]_n, respectively. 3 consists of a protonated H₂dien²⁺ cation and a 1-D straight chain built from [MnS₄] and [GeS₄] tetrahedra sharing opposite edges, and is the only example of a chelating amine uncoordinated to a transition metal ion. Both 4 and 5 consist of [Ge₂Se₆]^4- anions constructed by two [GeSe₄] tetrahedra sharing a common edge and discrete complex cations [V(en)₂(ea)]²⁺/[V(teta)(ea)]²⁺. 6 is composed of a [Ge₂Se₆]^4- anion and dinuclear complex cation [V₂(en)₆(μ-O)]⁴⁺ containing an en molecule as a rare monodentate ligand. Although some selenidogermanates with transition metal complexes have been successfully prepared, no selenidogermanates with trivalent vanadium complexes have been documented. Therefore, 4-6 offer the first examples of selenidogermanates with trivalent vanadium complexes under solvothermal conditions. Their optical and photocurrent response properties were studied.

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.

Three new metal chalcogenide open frameworks built through co-assembly and/or hybrid assembly from supertetrahedral T5-InOS and T3-InS nanoclusters

Reported here are three new metal chalcogenide open frameworks built from supertetrahedral T5-InOS (or o-T5) and T3-InS nanoclusters via co-assembly and/or hybrid assembly modes.

A multivalent mixed-metal strategy for single-Cu+-ion-bridged cluster-based chalcogenide open frameworks for sensitive nonenzymatic detection of glucose

Here we report two new metal-chalcogenide open frameworks (MCOFs) with large-sized supertetrahedral clusters bridged by an accessible single-cuprous ion via a multivalent mixed-metal strategy.

Room-Temperature Synthesis of Thiostannates from {[Ni(tren)]2[Sn2S6]}n

The compound {[Ni(tren)]2[Sn2S6]}n (1) (tren = tris(2-aminoethyl)amine, C6H18N4) was successfully applied as source for the room-temperature synthesis of the new thiostannates [Ni(tren)(ma)(H2O)]2[Sn2S6]·4H2O (2) (ma = methylamine, CH5N) and [Ni(tren)(1,2-dap)]2[Sn2S6]·2H2O (3) (1,2-dap = 1,2-diaminopropane, C3H10N2). The Ni-S bonds in the Ni2S2N8 bioctahedron in the structure of 1 are analyzed with density functional theory calculations demonstrating significantly differing Ni-S bond strengths. Because of this asymmetry they are easily broken in the presence of an excess of ma or 1,2-dap immediately followed by Ni-N bond formation to N donor atoms of the amine ligands thus generating [Ni(tren)(amine)](2+) complexes. The chemical reactions are fast, and compounds 2 and 3 are formed within 1 h. The synthesis concept presented here opens hitherto unknown possibilities for preparation of new thiostannates.

Supramolecular hexagonal nano tubes assembled by vanadium diamine complexes with thiogermanates

A supramolecular hexagonal nano tube is characterized, which is assembled by oxo-vanadium thiogermanate in a sulfur–diamine reduction system.

Synthesis of Crystalline Chalcogenides in Ionic Liquids

Crystalline chalcogenides belong to the most promising class of materials. In addition to dense solid-state structures, they may form molecular cluster arrangements and networks with high porosity, as in the so-called "zeotype" chalcogenidometalates. The high structural diversity comes along with interesting physical properties such as semi-/photoconductivity, ion transport capability, molecular trapping potential, as well as chemical and catalytic activity. The great interest in the development of new and tailored chalcogenides has provoked a continuous search for new and better synthesis strategies over the years. The trend has clearly been towards lower temperatures for both economic and ecological reasons as well as for better reaction control. This led to the application of ionic liquids as a designer-like medium for materials synthesis. In this Review, we summarize recent developments and present a survey of different chalcogenide families along with their properties.

Threading chalcogenide layers with polymer chains

Inserting polymers into a crystalline inorganic matrix to understand the structure, position, and the structure-property relationships of the resulting composites is important for designing new inorganic-organic materials and tuning their properties. Single crystals of polymer-chalcogenide composites were successfully prepared by trapping polyethyleneglycol within a selenidostannate matrix under surfactant-thermal conditions. This work might provide a new strategy for preparing novel crystalline polymer-inorganic composites through encapsulating polymer chains within inorganic matrices.

[Mn(dien)2]MnSnS4, [Mn(1,2-dap)]2Sn2S6 and [Mn(en)2]MnGeS4: from 1D anionic and neutral chains to 3D neutral frameworks

Three new organic–inorganic hybrid manganese thiogermanates and thiostannates with 1D anionic or neutral chains and 3D neutral frameworks have been synthesized and feature interesting antiferromagnetic or ferromagnetic properties.

A hybrid linkage mode between T2,2 and T3 selenide clusters

The synthesis and structural characterization of a multi-level 3D selenide framework with a novel T2,2–T3 linkage mode.