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The term self-assembly is used to describe the formation of many molecules and supramolecular architectures, but often, the precise mechanism is neglected. Here, we have investigated the kinetics of the self-assembly of the simplest heteropolyoxoanion, the Keggin ion [XMo12O40]x–. This study used variable temperature UV/vis spectroscopy to show that the Keggin ion can catalyze its own formation via an autocatalytic cycle. Kinetic investigations with real-time monitoring of the [XMo12O40]x– family’s formation reaction revealed key traits of autocatalytic systems, including kinetic saturation and concentration dependence of the incubation period. We explored the effect of the heteroatom on the kinetics of the autocatalytic process by investigating and comparing the formation rates of {AsMo12} and {SiMo12}. Finally, real-time electrospray ionization mass spectrometry studies of the reaction mixtures assist in the identification of the species involved in the formation process of the Keggin species, and these were explored using a stochastic model, which confirms our experimental observations.

The hydrolytically stable dioxime ligand (2Z-6Z)-piperidine-2,6-dione (H3pidiox) acts as a strong chelator mainly with hard metals in high oxidation states, a pre-requisite for potential applications in metal sequestering processes from aqueous solutions. Reaction of ZrCl4 with H3pidiox in methanol gives the mononuclear compound [ZrIV(η1,η1,η2-H2pidiox-O,N,O′)2(OH2)2]Cl2·H2O·CH3OH (1), while the same reaction mixture in the presence of KOH gave the pentanuclear ZrOC [ZrIV5(μ2-OH)4(OH2)4(μ2–η1,η1,η2-Hpidiox-O,N,O′)4(η1,η1,η1-HpidioxO,N,O′)4]·5KCl·3CH3OH·8H2O (2). Compound 1 is formed at very acidic pH = 0, and the pentanuclear ZrOC 2 at higher pH values (pH = 2). Compounds 1 and 2 were characterized by single crystal X-ray structure analysis, multi-nuclear NMR spectroscopy and ESI-MS spectrometry. The single crystal X-ray structure analysis of 1 revealed a mononuclear zirconium(IV) compound containing an eight-coordinate zirconium atom bound to two singly deprotonated H2pidiox− ligands and two water molecules in a severely distorted bicapped octahedral geometry. The pentanuclear ZrOC 2 constitutes the second example of a Zr5 cluster to be reported and the first one in which the four zirconium atoms are arranged in a tetrahedral arrangement with the fifth occupying the center of the tetrahedron. 1D and 2D NMR spectroscopies of the acidic CD3OD solutions of complex 1 reveal a fast equilibrium between 1 and 2. Addition of KOH into a CH3OH solution of 2 results in the controlled fast transformation of 2 to an asymmetric hexanuclear ZrOC 3 as evidenced by the NMR and real-time ESI-MS solution studies. Further addition of KOH to the solution of 3 leads to the ZrOC 4, and on the basis of NMR and ESI-MS data and in comparison with the known hexanuclear titanium(IV)/H3pidiox cluster, it is concluded that the cluster 4 should have a hexanuclear structure. Electrospray ionization mass spectrometry (ESI-MS) demonstrated not only the structural stability 1 and 2 in solution, but also revealed the reversible pH driven dis-assembly/re-assembly process between the monomeric 1 and the pentanuclear ZrOC 2.

Mixed-valent polyoxometalate (POM) clusters are one of the most interesting host species, showing a wide range of structural features and properties. The facile preparation and functionalisation of a mixed-valent polyoxofluorovanadates is reported, where two electrons are trapped to antipodal sites of the clusters. The first members of this family of clusters with the general formula, [VV12VIV2O16(?-O)10(?3-O)10(?3-F)2(L)2]6?, where L: py=pyridine?(1) pyr=pyrazine?(2) im=imidazole?(3), are unique organic-inorganic hybrids with the addition of a N-donor ligand at either end of the polyoxofluorovanadate. The composition and connectivity of 1?3 were characterised by single-crystal X-ray diffraction and electrospray ionisation mass spectrometry. Electron paramagnetic resonance spectroscopy revealed that the two well-separated VIV ions in each cluster are fully uncoupled with J=0, giving a degenerate singlet?triplet ground state. This attenuation of the exchange interaction is probed with density functional theoretical calculations that reveal that the inclusion of the fluoride ion in the cluster produces a bond pathway biased toward destructive interference between competing ferromagnetic and antiferromagnetic interactions. These robust molecular materials are the ideal combination of desirable electronic properties, with an organic handle with which they can be integrated into spintronic circuitry for molecular devices. 24 15 3836 3845

Phosphoester hydrolysis is an important chemical step in DNA repair. One archetypal molecular model of phosphoesters is para-nitrophenylphosphate (pNPP). It has been shown previously that the presence of molecular metal oxide [Mo7O24]6− may catalyse the hydrolysis of pNPP through the partial decomposition of polyoxomolybdate framework resulting in a [(PO4)2Mo5O15]6− product. Real-time monitoring of the catalytic system using electrospray ionisation mass spectrometry (ESI-MS) provided a glance into the species present in the reaction mixture and identification of potential catalytic candidates. Following up on the obtained spectrometric data, Density Functional Theory (DFT) calculations were carried out to characterise the hypothetical intermediate [Mo5O15(pNPP)2(H2O)6]6− that would be required to form under the hypothesised transformation. Surprisingly, our results point to the dimeric [Mo2O8]4− anion resulting from the decomposition of [Mo7O24]6− as the active catalytic species involved in the hydrolysis of pNPP rather than the originally assumed {Mo5O15} species. A similar study was carried out involving the same species but substituting Mo by W. The mechanism involving W species showed a higher barrier and less stable products in agreement with the non-catalytic effect found in experimental results.

Two-dimensional organic–inorganic hybrid materials based on layered double hydroxides (LDHs) have drawn significant attention during the last decade. The development of such materials is usually based on the intercalation of LDHs. However, the direct intercalation of organic guest molecules into the gallery of LDHs using carbonate-intercalated LDHs as the starting material is still challenging. To this end, we propose here a new approach with general applicability in the efficient de-carbonation and direct intercalation of LDHs using organic acids. The intercalation mechanism has been investigated in detail using acetic acid as a proof of concept. It is demonstrated that the interlayer carbonates of LDHs are converted into carbon dioxides in the presence of acetic acid, thus leaving acetates as counter-anions within the gallery of LDHs. The feasibility of the methods has been examined using LDHs of different lateral sizes and layer compositions. As a result, various aliphatic and aromatic organic anions including carboxylates, sulfonates and phosphonates have been successfully intercalated into the galleries of LDHs. Moreover, aggregation-induced emission molecules have also been intercalated into LDHs to develop a new type of photo-luminescent hybrid material that exhibits enhanced fluorescence and quantum yield. Therefore, this work provides a new approach for the facile preparation of LDH hybrids and design of hybrid materials for applications in diverse fields such as energy, the environment, medicine, and catalysis.

The chiral dicobalt(II) complex [CoII2(μ2-L)2] (1) (H2L = N2,N6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide) and its tert-butyl analogue [CoII2(μ2-LBu)2] (2) were synthesized and structurally characterized. Addition of one equivalent of AgSbF6 to the dichloromethane solution of 1 and 2 resulted in the isolation of the mixed-valent dicobalt(III,II) species [CoIIICoII(μ2-L)2]SbF6 (3) and [CoIIICoII(μ2-LBu)2]SbF6 (4). Homovalent 1 and 2 exhibited catalytic activity towards proton reduction in the presence of acetic acid (AcOH) as the substrate. The complexes are stable in solution while their catalytic turnover frequency is estimated at 10 and 34.6 h−1 molcat−1 for 1 and 2, respectively. Calculations reveal one-electron reduction of 1 is ligand-based, preserving the dicobalt(II) core and activating the ligand toward protonation at the quinoline group. This creates a vacant coordination site that is subsequently protonated to generate the catalytically ubiquitous Co(III) hydride. The dinuclear structure persists throughout where the distal Co(II) ion modulates the reactivity of the adjacent metal site by promoting ligand redox activity through spin state switching.

Reaction of the cyclic ligand (2Z,6Z)-piperidine-2,6-dione dioxime with TiCl4 and KOH yielded the hexanuclear cluster K6[TiIV6(μ3-O)2(μ2-O)3(CH3O)6(μ2–η1,η1,η2-Hpidiox-O,N,O′)4(μ2–η1,η1,η2-pidiox-O,N,O′)2]·7.5CH3OH possessing a new {Ti6O5} structural motif. The cluster core {Ti6O5} is wrapped by external tripodal imide dioxime ligands, showing good solubility and stability and thus, allowing its solution to be studied by means of electrospray ionization mass spectrometry, electrochemistry and 2D NMR, c. w. EPR and UV-vis spectroscopies. Density Functional Theory (DFT) calculations reveal that the cyclo-Ti3 metallic cores exhibit metallaromaticity which is expected to contribute to the stabilization of this system. 48 17 5551 5559