Selective C-H Activation of Molecular Nanodiamonds via Photoredox Catalysis

While substituted adamantanes have widespread use in medicinal chemistry, materials science, and ligand design, the use of diamantanes and higher diamondoids is limited to a much smaller number. Selective functionalization beyond adamantane is challenging, as the number of very similar types of C-H bonds (secondary, 2°, and tertiary, 3°) increases rapidly, and H atom transfer does not provide a general solution for site selectivity. We report a method using pyrylium photocatalysts that is effective for nanodiamond functionalization in up to 84% yield with exclusive 3° selectivity and moderate levels of regioselectivity between 3° sites. The proposed mechanism involving photooxidation, deprotonation, and radical C-C bond formation is corroborated through Stern-Volmer luminescence quenching, cyclic voltammetry, and EPR studies. Our photoredox strategy offers a versatile approach for the streamlined synthesis of diamondoid building blocks.

Hybrid bronzes: mixed-valence organic-inorganic metal oxides as a tunable material platform

We demonstrate that mixed-valence layered organic-inorganic metal oxides of the form (L)zHxMO3 (L = neutral ligand; M = Mo, W; z = 0.5, 1; 0 < x < 2), which we call hybrid bronzes, can be readily synthesized through mild solution-state self-assembly reactions to integrate the stability and electronic utility of inorganic metal oxide bronzes with the chemical diversity and functionality of organic molecules. We use single-crystal and powder X-ray diffraction coupled with X-ray, electronic, and vibrational spectroscopies to show that the products of aqueous pre-, mid-, or post-synthetic reduction are mixed-valence versions of highly crystalline layered hybrid oxides. Pillaring, bilayered, or canted bilayered arrangements of molecular arrays relative to inorganic sheets are dictated by judicious choice of organic ligands that can also incorporate chemical, redox, or photoactive handles. Significantly, bond-valence sum analysis and diffuse reflectance spectroscopy indicate relatively delocalized electronic behavior and four-point variable-temperature electrical transport measurements show that hybrid bronzes have comparable conductivity to their all-inorganic parent compounds. This work establishes a solution-processable, inexpensive, air- and water-stable, and non-toxic material family whose electronic bands can be readily tuned and doped, thereby positioning hybrid bronzes to address myriad material challenges.

Synthesis and structural characterization of a new heterometallicmolybdate coordination polymer based on a µ3-bridging amino alcohol

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.

Isolated molybdenum-based microporous POMs for selective adsorption of gases

Dodecanuclear, icosanuclear and octanuclear porous MOF-like POMs materials [MoV12O12(μ2-O)4(μ3-O)12(Htrz)4(trz)4]∙nH2O (n = 22, 1; n = 92, 2; Htrz = 1H-1,2,3-triazole), [MoV8O8(μ2-O)12(Htrz)8]½∙[MoV12O12(μ2-O)4(μ3-O)12(Htrz)4(trz)4]∙44H2O (3), and [MoV8O8(μ2-O)12(Htrz)8]·62H2O (4) have been obtained and well...

Bifunctional Microwave-Assisted Molybdenum-Complex Carbon Sponge Production for Supercapacitor and Water-Splitting Applications

The synthesis of dual-function molybdenum (Mo)-complex carbonous sponges is reported for elucidating their utilization as positive and negative electrodes in electrochemical devices and their applicability to the active oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in electrocatalytic devices. Molybdenum (Mo)-coordinated polyvinyl alcohol gel is converted into a porous Mo-complex nitrogen-rich carbonous sponge (MNCS) via microwave and low-temperature-annealing processes as a positive electrode. This MNCS was further thermally treated at a higher temperature to prepare a more carbonized Mo-complex N-doped carbon sponge (cMNCS) as a negative electrode. Both sponges were lightweight and porous and exhibited excellent specific capacitances of 562 F g^-1 as a positive MNCS electrode and 937 F g^-1 as a negative cMNCS electrode. The asymmetric supercapacitor assembled using them reveals a power density of 887.5 W kg^-1 at an energy density of 36 Wh kg^-1, in addition to a retention rate of >95% after 5000 cycles. We furthermore demonstrate the electrocatalytic capabilities of these materials with overpotentials of -170 and -220 mV for the HER and 1.70 and 1.53 V for the OER at a current density of 10 mA cm^-2 using a water-splitting electrocatalyzer.

Synthesis, Crystal Structure, and Luminescence of Cadmium(II) and Silver(I) Coordination Polymers Based on 1,3-Bis(1,2,4-triazol-1-yl)adamantane

Coordination polymers with a new rigid ligand 1,3-bis(1,2,4-triazol-1-yl)adamantane (L) were prepared by its reaction with cadmium(II) or silver(I) nitrates. Crystal structure of the coordination polymers was determined using single-crystal X-ray diffraction analysis. Silver formed two-dimensional coordination polymer [Ag(L)NO₃]_n, in which metal ions are linked by 1,3-bis(1,2,4-triazol-1-yl)adamantane ligands, coordinated by nitrogen atoms at positions 2 and 4 of 1,2,4-triazole rings. Layers of the coordination polymer consist of rare 18- and 30-membered {Ag₂L₂} and {Ag₄L₄} metallocycles. Cadmium(II) nitrate formed two kinds of one-dimensional coordination polymers depending on the metal-to-ligand ratio used in the synthesis. Coordination polymer [Cd(L)₂(NO₃)₂]_n was obtained in case of a 1:2 M:L ratio, while for M:L = 2:1 product {[Cd(L)(NO₃)₂(CH₃OH)]·0.5CH₃OH}_n was isolated. All coordination polymers demonstrated ligand-centered emission near 450 nm upon excitation at 370 nm.

New Coordination Polymers of Zinc(II), Copper(II) and Cadmium(II) with 1,3-Bis(1,2,4-triazol-4-yl)adamantane

The new coordination polymers (CPs) [Zn(tr2ad)Cl2]n, {[Cu(tr2ad)Cl]Cl∙4H2O}n, [Cd2(tr2ad)Cl4]n, {[Cu(tr2ad)(NO3)](NO3)}n and {[Cd(tr2ad)(NO3)](NO3)∙H2O}n were obtained in the form of air- and moisture-stable microcrystalline powders by the solvothermal reactions of zinc(II), copper(II) and cadmium(II) chlorides or nitrates with the ligand 1,3-bis(1,2,4-triazol-4-yl)adamantane (tr2ad). Investigation of the thermal behaviour assessed the thermal stability of these CPs, with [Cd2(tr2ad)Cl4]n starting to decompose only around 365 °C. As retrieved by powder X-ray diffraction, while [Zn(tr2ad)Cl2]n features 1-D chains along which the metal centre shows a tetrahedral geometry and the spacer is exo-bidentate, the other CPs contain 2-D double-layers in which the metal ions possess an octahedral stereochemistry and the linker is exo-tetradentate. A comparative structural analysis involving known coordination compounds containing the tr2ad ligand enabled us to disclose (i) the versatility of the ligand, as far as the coordination modes are concerned; (ii) the variability in crystal structure dimensionality, ranging from 1-D to 3-D; (iii) the fact that, to the best of our knowledge, [Zn(tr2ad)Cl2]n is the first ZnII-based CP containing the tr2ad spacer.

Crystal structure and Hirshfeld surface analysis of 4,4'-(propane-1,3-diyl)bis(4H-1,2,4-triazol-1-ium) penta-fluorido-oxidovanadate(V)

In the structure of the title salt, (C7H12N6)[VOF5], second-order Jahn-Teller distortion of the coordination octa-hedra around V ions is reflected by coexistence of short V-O bonds [1.5767 (12) Å] and trans-positioned long V-F bonds [2.0981 (9) Å], with four equatorial V-F distances being inter-mediate in magnitude [1.7977 (9)-1.8913 (9) Å]. Hydrogen bonding of the anions is restricted to F-atom acceptors only, with particularly strong N-H⋯F inter-actions [N⋯F = 2.5072 (15) Å] established by axial and cis-positioned equatorial F atoms. Hirshfeld surface analysis indicates that the most important inter-actions are overwhelmingly H⋯F/F⋯H, accounting for 74.4 and 36.8% of the contacts for the individual anions and cations, respectively. Weak CH⋯F and CH⋯N bonds are essential for generation of three-dimensional structure.

A Molybdenum Trioxide Hybrid Decorated by 3-(1,2,4-Triazol-4-yl)adamantane-1-carboxylic Acid: A Promising Reaction-Induced Self-Separating (RISS) Catalyst

3-(1,2,4-Triazol-4-yl)adamantane-1-carboxylic acid (tradcH), a heterobifunctional organic ligand in which carboxylic acid and 1,2,4-triazole groups are united through a rigid 1,3-adamantanediyl spacer, was employed for the synthesis of a Mo^VI oxide organic hybrid. The ligand crystallized from water as tradcH·H₂O (1), possessing a two-dimensional hydrogen-bonding network, and from ethanol as a cyclic molecular solvate with the composition (tradcH)₃·2EtOH (2). Treatment of tradcH with MoO₃ under hydrothermal conditions afforded a new Mo trioxide hybrid, [MoO₃(tradcH)]·H₂O (3), which was structurally characterized. In 3, the molybdenum atoms form a polymeric zigzag chain of {μ₂-O-MoO₂}_n which is supported by double triazole bridges, while the carboxylic acid termini are left uncoordinated. The coordination environment of the Mo centers appears as distorted cis-{MoN₂O₄} octahedra. The hybrid exhibits high thermal stability (up to 270 °C) and was employed for a relatively broad scope of catalytic oxidation reactions in the liquid phase. Its catalytic behavior may be compared to a reversible mutation, featuring the best sides of homogeneous and heterogeneous catalysis. The original solid material converts into soluble active species, and the latter revert to the original material upon completion of the catalytic reaction, precipitating and allowing straightforward catalyst separation/reuse (like a heterogeneous catalyst). This catalyst was explored for a chemical reaction scope covering sulfoxidation, oxidative alcohol dehydrogenation, aldehyde oxidation, and olefin epoxidation, using hydrogen peroxide as an eco-friendly oxidant that gives water as a coproduct.

Geomimetic approaches in the design and synthesis of metal-organic frameworks

The recent discovery of minerals with metal-organic framework (MOF) structures has challenged the view of MOFs as purely synthetic materials. At the same time, the application of geo-inspired synthetic methodologies, such as accelerated ageing and pseudomorphic replication, has enabled a cleaner, more environmentally friendly synthesis of MOFs from mineral-like feedstocks, as well as the assembly of materials with structure controlled at both micro- and meso-scales. These almost concomitant developments have highlighted the previously unknown relationships between geology and MOF chemistry. Here, we outline examples of MOF structures found in minerals, and note geologically inspired approaches to MOF synthesis, as a means to highlight how the emergent geomimetic concepts in MOF chemistry can lead to advances in the design and synthesis of MOFs. This article is part of the theme issue 'Mineralomimesis: natural and synthetic frameworks in science and technology'.

On the Border between Low-Nuclearity and One-Dimensional Solids: A Unique Interplay of 1,2,4-Triazolyl-Based {CuII5(OH)2} Clusters and MoVI-Oxide Matrix

A pentanuclear Cu^II₅-hydroxo cluster possessing an unusual linear-shaped configuration was formed and crystallized under hydrothermal conditions as a result of the unique cooperation of bridging 1,2,4-triazole ligand ( trans-1,4-cyclohexanediyl-4,4'-bi(1,2,4-triazole) ( tr₂ cy)), Mo^VI-oxide, and CuSO₄. This structural motif can be rationalized by assuming in situ generation of {Cu₂Mo₆O₂₂}^4- anions, which represent heteroleptic derivatives of γ-type [Mo₈O₂₆]^4- further interlinked by [Cu₃(OH)₂]⁴⁺ cations through [ N- N] bridges. The framework structure of the resulting compound [Cu₅(OH)₂( tr₂ cy)₂Mo₆O₂₂]·6H₂O (1) is thus built up from neutral heterometallic {Cu₅(OH)₂Mo₆O₂₂} _n layers pillared with tetradentate tr₂ cy. Quantum-chemical calculations demonstrate that the exclusive site of the parent γ-[Mo₈O₂₆]^4- cluster into which Cu^II inserts corresponds with the site that has the lowest defect ("MoO₂ vacancy") formation energy, demonstrating how the local metal-polyoxomolybdate chemistry can express itself in the final crystal structure. Magnetic susceptibility measurements of 1 show strong antiferromagnetic coupling within the Cu₅ chain with exchange parameters J₁ = -500(40) K (-348(28) cm^-1), J₂ = -350(10) K (-243(7) cm^-1) and g = 2.32(2), χ² = 6.5 × 10^-4. Periodic quantum-chemical calculations reproduce the antiferromagnetic character of 1 and connect it with an effective ligand-mediated spin coupling mechanism that comes about from the favorable structural arrangement between the Cu centers and the OH^-, O^2-, and tr₂ cy bridging ligands.

High-yield synthesis and catalytic response of chainlike hybrid materials of the [(MoO3)m(2,2′-bipyridine)n] family

MoO₃/2,2′-bipyridine hybrids have been prepared (hydro)thermally from [MoO₃(2,2′-bipy)] and compared as catalysts in styrene oxide ethanolysis and olefin epoxidation.

A combined continuous wave electron paramagnetic resonance and DFT calculations of copper-doped 3∞[Cd0.98Cu0.02(prz-trz-ia)] metal–organic framework

Successful combination of EPR and DFT was applied for investigation the novel heteronuclear MOF compounds.

Crystal Structure and Catalytic Behavior in Olefin Epoxidation of a One-Dimensional Tungsten Oxide/Bipyridine Hybrid

The tungsten oxide/2,2'-bipyridine hybrid material [WO3(2,2'-bpy)]·nH2O (n = 1-2) (1) has been prepared in near quantitative yield by the reaction of H2WO4, 2,2'-bpy, and H2O in the mole ratio of ca. 1:2:700 at 160 °C for 98 h in a rotating Teflon-lined digestion bomb. The solid-state structure of 1 was solved and refined through Rietveld analysis of high-resolution synchrotron X-ray diffraction data collected for the microcrystalline powder. The material, crystallizing in the orthorhombic space group Iba2, is composed of a one-dimensional organic-inorganic hybrid polymer, ∞(1)[WO3(2,2'-bpy)], topologically identical to that found in the previously reported anhydrous phases [MO3(2,2'-bpy)] (M = Mo, W). While in the latter the N,N'-chelated 2,2'-bpy ligands of adjacent corner-shared {MO4N2} octahedra are positioned on the same side of the 1D chain, in 1 the 2,2'-bpy ligands alternate above and below the chain. The catalytic behavior of compound 1 for the epoxidation of cis-cyclooctene was compared with that for several other tungsten- or molybdenum-based (pre)catalysts, including the hybrid polymer [MoO3(2,2'-bpy)]. While the latter exhibits superior performance when tert-butyl hydroperoxide (TBHP) is used as the oxidant, compound 1 is superior when aqueous hydrogen peroxide is used, allowing near-quantitative conversion of the olefin to the epoxide. With H2O2, compounds 1 and [MoO3(2,2'-bpy)] act as sources of soluble active species, namely, the oxodiperoxo complex [MO(O2)2(2,2'-bpy)], which is formed in situ. Compounds 1 and [WO(O2)2(2,2'-bpy)] (2) were further tested in the epoxidation of cyclododecene, trans-2-octene, 1-octene, (R)-limonene, and styrene. The structure of 2 was determined by single-crystal X-ray diffraction and found to be isotypical with the molybdenum analogue.

The functionalization of nanodiamonds (diamondoids) as a key parameter of their easily controlled self-assembly in micro- and nanocrystals from the vapor phase

We detail herein readily accessible processes to control previously unobserved robust self-assemblies of nanodiamonds (diamondoids) in micro- and nanocrystals from their mild vapor deposition. The chemical functionalization of uniform and discernible nanodiamonds was found to be a key parameter, and depending on the type of functional group (hydroxy, fluorine, etc.) and its position on the diamondoid, the structure of the discrete deposits can vary dramatically. Thus, well-defined anisotropic structures such as rod, needle, triangle or truncated octahedron shapes can be obtained, and self-assembled edifices of sizes ranging from 20 nm to several hundred micrometers formed with conservation of a similar structure for a given diamondoid. Key thermodynamic data including sublimation enthalpy of diamondoid derivatives are reported, and the SEM of the self-assemblies coupled with EDX analyses and XRD attest the nature and purity of nanodiamond crystal deposits. This attractive method is simple and outperforms in terms of deposit quality dip-coating methods we used. This vapor phase deposition approach is expected to allow for an easy formation of diamondoid nanoobjects on different types of substrates.

A rare I2O3 hybrid organic–inorganic material with high connectivity and quadruple-stranded helices

A novel I²O³ hybrid material with one Cd–OH helix, two quadruple-stranded Cd–ligand helices and a (5,14-c) topological net was assembled.

1,2,4-Triazole functionalized adamantanes: a new library of polydentate tectons for designing structures of coordination polymers

A series of functionalized adamantanes: 1,3-bis(1,2,4-triazol-4-yl)(tr(2)ad); 1,3,5-tris(1,2,4-triazol-4-yl)-(tr(3)ad); 1,3,5,7-tetrakis(1,2,4-triazol-4-yl)adamantanes (tr(4)ad) and 3,5,7-tris(1,2,4-triazol-4-yl)-1-azaadamantane (tr(3)ada) were developed as a new family of geometrically rigid polydentate tectons for supramolecular synthesis of framework solids. The coordination compounds were prepared under hydrothermal conditions; their structures reveal a special potential of the triazolyl adamantanes for the generation of highly-connected and open frameworks as well as structures based upon polynuclear metal clusters assembled with short-distance N(1),N(2)-triazole bridges. Complexes [Cd{L}(2)]A·nH(2)O [L = tr(3)ad, A = 2NO(3)(-) (4), CdCl(4)(2-) (5); L = tr(3)ada, A = CdI(4)(2-) (7)] are isomorphous and adopt a layered 3,6-connected structure of CdI(2) type. [{Cu(3)(OH)}(2)(SO(4))(5)(H(2)O)(2){tr(3)ad}(3)]·26H(2)O (6) is a layered polymer based upon Cu(3)(μ(3)-OH) nodes and trigonal tr(3)ad links. In [Cu(3)(OH)(2){tr(3)ada}(2)(H(2)O)(4)](ClO(4))(4) (8), [Cu(2){tr(3)ada}(2)(H(2)O)(3)](SO(4))(2)·7H(2)O (9) and [Cd(2){tr(3)ada}(3)]Cl(4)·28H(2)O (10) (UCl(3)-type net) the organic tripodal ligands bridge polynuclear metal clusters. Complexes [Ag{tr(4)ad}]NO(3)·3.5H(2)O (11) and [Cu{tr(4)ad}(H(2)O)](ClO(4))(2)·3H(2)O (12) have 3D SrAl(2)-type frameworks with the metal ions and adamantane tectons as topologically equivalent tetrahedral nodes, while in [Cd(3)Cl(6){tr(4)ad}(2)]·9H(2)O (13) the ligands bridge trinuclear six-connected Cd(3)Cl(6)(μ-tr)(4)(tr)(2) clusters. In the compounds [Cd(2){tr(2)ad}(4)(H(2)O)(4)](CdBr(4))(2)·2H(2)O (2) and [Cd{tr(2)ad}(4){CdI(3)}(2)]·4H(2)O (3) the bitopic ligands provide simple links between the metal ions, while in [Ag(2){tr(2)ad}(2)](NO(3))(2)·2H(2)O (1) the ligand is tetradentate and generates a 3D framework.