We provide a systematic overview of the mechanochemical reactions of inorganic solids, notably simple binary compounds, such as oxides, nitrides, carbides, sulphides, phosphides, hydrides, borides, borane derivatives, and related systems. Whereas the solid state has been traditionally considered to be of little synthetic value by the broader community of synthetic chemists, the solid-state community, and in particular researchers focusing on the reactions of inorganic materials, have thrived in building a rich and dynamic research field based on mechanically-driven transformations of inorganic substances typically seen as inert and high-melting. This review provides an insight into the chemical richness of such mechanochemical reactions and, at the same time, offers their tentative categorisation based on transformation type, resulting in seven distinct groupings: (i) the formation of adducts, (ii) the reactions of dehydration; (iii) oxidation-reduction (redox) reactions; (iv) metathesis (or exchange) reactions; (v) doping and structural rearrangements, including reactions involving the reaction vessel (the milling jar); (vi) acid-base reactions, and (vii) other, mixed type reactions. At the same time, we offer a parallel description of inorganic mechanochemical reactions depending on the reaction conditions, as those that: (i) take place under mild conditions (e.g., manual grinding using a mortar and a pestle); (ii) proceed gradually under mechanical milling; (iii) are self-sustained and initiated by mechanical milling, i.e., mechanically induced self-propagating reactions (MSRs); and (iv) proceed only via harsh grinding and are a result of chemical reactivity under strongly non-equilibrium conditions. By elaborating on typical examples and general principles in the mechanochemistry of hard and high-melting substances, this review provides a suitable complement to the existing literature, focusing on the properties and mechanochemical reactions of inorganic solids, such as nanomaterials and catalysts.
Nanostructures , Catalysis , Oxidation-Reduction , Oxides
In this study, we report two dinuclear Ru(II) complexes C1 and C2 and compare them to their mononuclear analogues Ref1 and Ref2. The dinuclear species exhibit a much stronger absorption, longer excited-state lifetimes and higher luminescence quantum yields than the mononuclear complexes. In addition, C1 and C2 are easier to reduce. An estimation of the driving forces for the electron transfer processes relevant to photocatalytic hydrogen evolution suggests that C1 and Ref2 possess similar activity as photosensitizer (PS). Yet, the improved photophysical properties of C1 make it a more promising candidate for hydrogen evolution. In hydrogen evolution experiments, C1 indeed exhibits increased activity as PS, however, the catalytic system loses its activity after only a few hours. C2 is less active than the mononuclear complexes despite its superior photophysical properties. This observation is attributed to a lack of driving force for the electron transfer towards the catalyst. Further studies of the dinuclear complex C1 show that it is indeed the PS, which decomposes under the catalytic conditions, presumably due to the electron transfer towards the catalyst being the rate-limiting step.
In this study, we extend the family of organosilyl-functionalized trivacant Keggin polyoxotungstates, [PW9O34(RSiOH)3]3- (R = nPr, iPr, tBu), through the introduction of bulky aryl and aliphatic silanol substituents, namely phenyl, cyclohexyl and biphenyl. This work was performed in order to study the impact of these large functional groups on the accessibility of the well-defined tridentate coordination site. Coordination of hafnium to these type II hybrid polyoxotungstates was conducted in order to study the ability of the bulkier ligand pockets to support larger cations in comparison to those previously reported (e.g. Ti4+, V3+, V5+, Ge4+). Increased steric hindrance around the coordination site from the biphenyl groups resulted in much longer reaction times for the complexation reaction compared to the other functional groups used, but the impact of our design toward stabilizing reactive species proved limited, as all complexes easily undergo hydrolysis of the Hf-OtBu bond in the presence of water. Electrochemical investigations of the ligands and hafnium complexes reveal that the redox events centered on the polyoxotungstate core can be tuned by varying the substituents on the silyl fragment, and exhibit a cathodic shift after coordination of the redox inactive tetravalent cation.
The structure-properties relationship in a series of carbonyl rhenium(I) complexes based on substituted terpyridine ligands of general formula [Re(κxN-Rtpy)(CO)yL]n+ is explored by both experimental and theoretical methods. In these compounds, the terpyridine ligands adopt both bidentate (κ2N) and terdentate (κ3N) coordination modes associated with three or two carbonyls, respectively. Conversion from the κ2N to the κ3N coordination mode leads to large changes in the absorption spectra and oxidation potentials due to destabilization of the HOMO level of each complex. The absorption profiles of the κ3N complexes cover the whole visible spectra with lower maxima around 700 nm, tailing out to 800 nm, while no emission is observed with Br- as the axial ligand L. When the axial ligand is modified from the native halide to pyridine or triphenylphosphine, the lowest absorption band is blue-shifted by 60 and 90 nm, respectively. These cationic complexes are near-infrared emitters with emission maxima between 840 and 950 nm for the pyridine compounds and 780-800 nm for the triphenylphosphine compounds.
The photocatalytic reduction of water to form hydrogen gas (H2) is a promising approach to collect, convert, and store solar energy. Typically, ruthenium tris(bipyridine) and its many derivatives are used as photosensitizers (PSs) in a variety of photocatalytic conditions. The bis(terpyridine) analogues, however, have only recently gained attention for this application because of their poor photophysical properties. Yet, by the introduction of electron-donating or -withdrawing groups on the terpyridine ligands, the photophysical and electrochemical properties can be considerably improved. In this study, we report a series of nonsymmetric 2,6-di(pyridin-2-yl)pyrimidine ligands with peripheral pyridine substituents in different positions and their corresponding ruthenium(II) complexes. The presence of the pyrimidine ring stabilizes the lowest unoccupied molecular orbital, leading to a red-shifted emission and prolonged excited-state lifetimes as well as higher luminescence quantum yields compared to analogous terpyridine complexes. Furthermore, all complexes are easier to reduce than the previously reported bis(terpyridine) complexes used as PSs. Interestingly, the pyridine substituent in the 4-pyrimidine position has a greater impact on both the photophysical and electrochemical properties. This correlation between the substitution pattern and properties of the complexes is further investigated by using time-dependent density functional theory. In hydrogen evolution experiments under blue- and red-light irradiation, all investigated complexes exhibit much higher activity compared to the previously reported ruthenium(II) bis(terpyridine) complexes, but none of the complexes are as stable as the literature compounds, presumably because of an additional decomposition pathway of the reduced PS competing with electron transfer from the reduced PS to the catalyst.
The complexation of actinide cations by polyoxometalates (POMs) has been extensively studied over the past 50 years. In this perspective article, we present the rich structural diversity of actinide-POM complexes and their contribution to the extension of our knowledges of actinide chemistry, especially regarding aspect of their redox chemistry, as well as application for the capture and separation of these cations in the context of nuclear fuel remediation. These heterometallic assemblies have also proven highly valuable as model for heterogeneous systems based on actinides supported by metal oxide surfaces. In particular, activation of the An-O bond of actinyl fragments upon complexation with lacunary POMs has been reported, creating opportunities for future developments regarding the reactivity of these heterometallic assemblies.
Electronic communication between the linked metal centers in Ru(ii)-Re(i) dyads is tuned using the oxidation state (S and SO2) of sulfur-bridged ligands. Higher catalytic activity is seen for the SO2-bridged dyad in the photocatalytic reduction of CO2.
The binary assembly DDA-{Mo132}/OA-γ-Fe2O3 (DDA = didodecyldimethylammonium, {Mo132} = [Mo132O372(CH3COO)30(H2O)72]42-, OA = oleic acid) constitutes one of the two examples in the literature of binary superlattices made of a mixing of nanocrystals and oxo-clusters. In a precedent work, we reported in details the preparation of such magnetic binary systems and studied the effect of the nature of the polyoxometalates (POMs) on the magnetic properties. In the present paper, we study the stability of this model binary assembly under heating at various temperatures. Indeed, especially if magnetic and/or transport properties are targeted, an annealing can be essential to change the phase of the nanocrystals in a more magnetic one and/or to desorb the organic capping of the nano-objects that can constitute an obstacle to the electronic communication between the nano-objects. We gave evidence that the maghemite organization in the binary assembly is maintained until 370°C under vacuum thanks to the presence of the POMs. This latter evolve in the phase MoO3, but still permits to avoid the aggregation of the nanocrystals as well as preserve their periodical arrangement. On the contrary, an assembly made of pure γ-Fe2O3 nanocrystals displays a clear aggregation of the nano-objects from 370°C, as attested by transmission and scanning electronic microscopies and confirmed by magnetic measurements. The stability of the magnetic nanocrystals in such POMs/nanocrystals assemblies opens the way to (i) the elaboration of new binary assemblies from POMs and numerous kinds of nanocrystals with a good control on the magnetic properties and to (ii) the investigation of new physical properties as exchange coupling, or magneto-transport in such systems.
Motivated by the recent report of a heteroleptic ruthenium bis-terpyridine complex [Ru(toltpy)(bipytpy)](PF6)2 (toltpy: 4'-(tolyl)-2,2':6',2''-terpyridine; bipytpy: 4'-(4-bromophenyl)-4,4''':4'',4''''-di-pyridinyl-2,2':6',2''-terpyridine) capable of driving the photo-evolution of hydrogen with a constant rate of activity for 12 days [M. Rupp et al., Inorg. Chem., 2019, 58, 9127-9134], we investigated the impact of an internal electron donor on the photoactivity of three new ruthenium bis-terpyridine photosensitizers. We used 4'-(N,N-dimethylaminophenyl)-4,4''-di-tert-butyl-2,2':6',2''-terpyridine (Dtpy) as the donor ligand. These complexes also bear peripheral coordination sites at various positions on the terpyridine backbone, allowing for photosensitizer-catalyst interactions. Their performances in photocatalysis under blue and green light (450 and 525 nm, respectively) were measured, in the presence of triethanolamine, using a cobaloxime catalyst [Co(dmgH)2(H2O)2](BF4)2. Complexes C1[Ru(Dtpy)(pytpy)](PF6)2 (pytpy: 4'-(pyridin-4-yl)-2,2':6',2''-terpyridine) and C3[Ru(Dtpy)(bipytpy)](PF6)2 appeared to have a photostability similar to that of [Ru(toltpy)(bipytpy)](PF6)2 but with lower activity rates, while C2[Ru(Dtpy)(pz2bpy)](PF6)2 (pz2bpy: 2,6-di(pyrazin-2-yl)-4,4'-bipyridine) showed a better peak activity, however, followed by a progressive decay. After 24 hours, complexes C1, C2 and C3 had reached TONs of 18, 35 and 52 under blue light and 14, 20 and 47 under green light, respectively, and were still found to be active. Their photophysical and electronic properties are discussed to rationalize the photocatalytic trends.
We report several new dyads constituted of cationic iridium(iii) photosensitizers and cobalt(iii) catalyst connected via free pendant pyridine on the photosensitizers. These dyads were studied by X-ray crystallography, electrochemistry, absorption and emission spectroscopy as well as theoretical calculations and were shown to efficiently produce H2 under visible light irradiation. In every case, the dyad outperformed the equivalent system without a pendant pyridine. The dependence between irradiation wavelength and photocatalytic performances was also studied, with H2 being evolved with turn-over numbers up to 295, 251, 188 and 78 molH2 molPS-1 under blue, green, yellow and red light, respectively.
Since the initial report by Lehn et al. in 1979, ruthenium tris(bipyridine) ([Ru(bpy)3]2+) and its numerous derivatives were applied as photosensitizers (PSs) in a large panel of photocatalytic conditions while the bis(terpyridine) analogues were disregarded because of their low quantum yields and short excited-state lifetimes. In this study, we prepared a new terpyridine ligand, 4'-(4-bromophenyl)-4,4â´:4â³,4â´'-dipyridinyl- 2,2':6',2â³-terpyridine (Bipytpy) and used it to prepare the heteroleptic complex [Ru(Tolyltpy)(Bipytpy)](PF6)2 (1; Tolyltpy = 4'-tolyl-2,2':6',2'-terpyridine). Complex 1 exhibits enhanced photophysical properties with a higher quantum yield (7.4 × 10-4) and a longer excited-state lifetime (3.8 ns) compared to those of [Ru(Tolyltpy)2](PF6)2 (3 × 10-5 and 0.74 ns, respectively). These enhanced photophysical characteristics and the potential for PS-catalyst interaction through the peripheral pyridines led us to apply the complex for visible-light-driven hydrogen evolution. The photocatalytic system based on 1 as the PS, triethanolamine as a sacrificial donor, and cobaloxime as a catalyst exhibits sustained activity over more than 10 days under blue-light irradiation (light-emitting diode centered at 450 nm). A maximum turnover number of 764 was obtained after 12 days.
An unusual photooxidation of a coordinated 4-mercaptopyridine ( SpyH) ligand in the [Ru(Hmctpy)(dmbpy)(κ S-SpyH)]2+complex (Hmctpy = 4'-carboxy-2,2';6',2â³-terpyridine, dmbpy = 4,4'-dimethyl-2,2'-bipyridine) takes place under visible and UV irradiation, in aerated acetonitrile. The [Ru(mctpy)(dmbpy)(κ S-SO2py)] sulfinato product has been characterized by a variety of methods, including X-ray diffraction which supports the presence of the Ru-κ S-SpyH isomer in the starting complex. The photooxidation of the 4-mercaptopyridine ligand enhances the back-bonding interactions in the complex by means of the strongly acceptor 4-pyridinesulfinato-SO2py species, increasing the redox potential of the Ru(III)/Ru(II) couple significantly from 1.23 to 1.62 V. It also led to pronounced changes in the electronic and NMR spectra of the complexes, corroborated by DFT and ZINDO-S calculations. A possible mechanism based on referenced data of photooxidation has been proposed, which involves the formation of a reactive oxygen species and intermediate endoperoxide species, yielding a very stable Ru-sulfinato product. This novel species exhibits stronger luminescence (Φ f = 0.004) than the starting complex under UV excitation.
A series of [Re(CO)3Br(N^N)] (N^N = substituted 2,2'-bipyridine ligand) complexes based on polypyridine-functionalized Dawson polyoxometalate (1-3) has been synthesized. The new hybrids (4-6) were characterized by various analytical techniques, including absorption, vibrational and luminescence spectroscopies as well as electrochemistry. Both units, the polyoxometalate and the transition metal complex, retain their intrinsic properties. Their combination in the newly prepared hybrids results in improved photosensitization in the high-energy visible region. However, a complete quenching of the emission for the [Re(CO)3Br(N^N)] complexes is observed due to formation of a charge separated state, Re(ii) - POM-, as shown by quenching experiments as well as theoretical modelling via DFT.
The synthesis of a Ir(III)-Co(III) dyad with vectorial electron transfer afforded a novel supramolecular system that photocatalytically produces hydrogen in a range extending from the blue region of the spectrum to the red region with higher turnover number and frequency compared to other bimetallic dyads.
Ten newly synthesized non-symmetric benzo[b]-fused BODIPYs are compared with an extended series of nine related families (23 compounds) to gain insights into their structure-property relationship. The insertion of a fused indole moiety into the dipyrromethene core and various substituents on the proximal aryl including fused aromatic groups, lead to pronounced changes in the properties of compounds . By taking advantage of this versatile synthetic platform that allows facile substituent modifications and extension of the π-conjugated system, significant bathochromic shifts in the absorption (λmax = 511-597 nm) and emission (601-757 nm) bands are achieved. Although the oxidation potentials of the compounds vary considerably throughout the series (+1.28-+1.65 V) due to the significant contribution of the aryl function to the HOMO, the reduction remains much more consistent (-0.61 to -0.79 V) as the LUMO resides primarily on the dipyrromethene core with little aryl contribution as calculated by DFT. For example, installation of a dimethylamine substituent in the para position of the aryl group leads to drastic modification of the optoelectronic properties of the absorption (597 nm) and emission (757 nm) maxima. The full electrochemical, photophysical and computational analyses of the compounds along with the structural characterization of compounds , , , and are used to rationalize the potential of this powerful platform.
In the present article, the successful coassembly of spherical 6.2 nm maghemite (γ-Fe2O3) nanocrystals and giant polyoxometalates (POMs) such as 2.9 nm {Mo132} is demonstrated. To do so, colloidal solutions of oleic acid-capped γ-Fe2O3 and long-chain alkylammonium-encapsulated {Mo132 } dispersed in chloroform are mixed together and supported self-organized binary superlattices are obtained upon the solvent evaporation on immersed substrates. Both electronic microscopy and small angles X-ray scattering data reveal an AB-type structure and an enhanced structuration of the magnetic nanocrystals (MNCs) assembly with POMs in octahedral interstices. Therefore, {Mo132} acts as an efficient binder constituent for improving the nanocrystals ordering in 3D films. Interestingly, in the case of didodecyldimethylammonium (C12)-encapsulated POMs, the long-range ordered binary assemblies are obtained while preserving the nanocrystals magnetic properties due to weak POMs-MNCs interactions. On the other hand, POMs of larger effective diameter can be employed as spacer blocks for MNCs as shown by using {Mo132} capped with dioctadecyldimethylammonium (C18) displaying longer chains. In that case, it is shown that POMs can also be used for fine-tuning the dipolar interactions in γ-Fe2O3 nanocrystal assemblies.
A new class of cationic iridium(III) complexes of the form [(C(â§)N)2Ir(N(â§)N)][PF6] is reported, where C(â§)N = cyclometallating 2-phenylpyridinato, ppy, or 2-(2,4-difluorophenyl)-5'-methylpyridinato, dFMeppy, and N(â§)N = guanidyl-pyridine, gpy, or -pyrazine, gpz, as the ancillary ligand. A large blue-shift in the emission coupled with a 7-to-9 fold enhancement in photoluminescence quantum yield and microsecond emission lifetimes were observed for the complexes containing the partially saturated gpy ligand as compared to the benchmark complex [(ppy)2Ir(bpy)][PF6], C1, where bpy is 2,2'-bipyridine.
Coordination Complexes/chemistry , Guanidine/chemistry , Iridium/chemistry , Luminescent Agents/chemistry , Pyrazines/chemistry , Pyridines/chemistry , Cations , Ligands , Luminescent Measurements , Models, Molecular , Molecular Structure
