On the formation of gold nanoparticles from [AuIIICl4]- and a non-classical reduced polyoxomolybdate as an electron source: A quantum mechanical modelling and experimental study

Polyoxometalate (POM)-mediated reduction and nucleation mechanisms in nanoparticle (NP) syntheses are still largely unknown. We carried out comprehensive theoretical analysis using density functional theory (DFT) to gain insight into the molecular and electronic changes that occur during the reduction of HAuIIICl4 with the Kabanos-type polyoxomolybdate, Na{(MoV2O4)3(µ2-O)3(µ2-SO3)3(µ6-SO3)}2]15-. In the system presented herein the electrons are supplied by the POM, making the computational thermodynamic analysis more feasible. Our results reveal that this particular POM is a multi-electron source and the proton-coupled electron transfer (PCET) greatly promotes the reduction process. Based on the energy and molecular orbital studies of the intermediate species the reduction of AuIII to AuI is shown to be thermodynamically favourable, and a low HOMO-LUMO gap of the POM-Au superstructure is advantageous for electron transfer. By modelling the reduction of three couples of AuIII ¿ AuI by the same POM unit, it is proposed that the reduced polyoxomolybdate is finally fully oxidised. The subjacent idea of using the Kabanos POM was confirmed by comprehensive experimental characterisation of POM-stabilised gold nanoparticles (AuNPs@POM). Present theoretical analysis suggests that protons have a significant influence on the final AuI to Au0 reduction step that ultimately leads to colloidal AuNPs@POM

Maximum aromaticity or maximum pentagon separation; Which is the origin behind the stability of endohedral metallofullerenes?

10.1039/C4FD00096JTwo different interpretations have been recently proposed to rationalize the stabilization of some hosting cages in endohedral metallofullerenes as a consequence of the larger localization of the negative charge on pentagonal rather than on hexagonal faces. We try to figure out the physical origin that mainly governs the stability of charged fullerenes; is it aromaticity or electrostatics

Relevance of thermal effects in the formation of endohedral metallofullerenes: The case of Gd3N@ C s(39663)-C 82 and other related systems

10.1021/ic302239eThermal contributions to the free energy have to be taken into account to rationalize the formation of Gd3N@Cs(39663)-C 82, a nitride endohedral metallofullerene that shows a carbon cage with two fused pentagons which is not predicted to have the lowest electronic energy among the isomers of C82. The lower symmetry and the larger number of pyracylene units of Cs(39663)-C82 with respect to the cage in the lowest-energy metallofullerene, C2v(39705)-C 82, favor its formation at high temperatures, as seen for other similar cage isomers that encapsulate metal clusters within the C80 and C82 families. These cages, which share common motifs with the prototypical Ih(7)-C80, are all related by C2 insertions/extrusions and Stone-Wales transformations

Electronic structure of IPR and non-IPR endohedral metallofullerenes: Connecting orbital and topological rules

10.1016/j.crci.2011.09.004The electronic structure of endohedral metallofullerenes is rationalized by connecting the apparently independent orbital and topological rules that explain the stability of this family of fullerenes. The separation of the 12 pentagons of the fullerene, which is maximized in order to minimize the Coulomb repulsion, is found to be correlated with the orbital energies of the cage that accepts the electron transfer from the internal cluster. An explanation for the absence of non-IPR cages in large-size EMFs is also provided

Polyoxometalates with internal cavities: redox activity, basicity, and cation encapsulation in [Xn+P5W30O110](15-n)- Preyssler complexes, with X = Na+, Ca2+, Y3+, La3+, Ce3+, and Th4+

The Preyssler anion, of general formula [

Redox-Active Behavior of the [{Ti(η5-C5Me5)(μ-NH)}3(μ3-N)] Metalloligand

10.1021/ic400463aTreatment of [Cl3Y{(µ3-NH)3Ti3(?5-C5Me5)3(µ3-N)}] with [K(C5Me5)] in toluene gives C10Me10 and the paramagnetic [K(µ-Cl)3Y{(µ3-NH)3Ti3(?5-C5Me5)3(µ3-N)}] (3) derivative. Crystallization of 3 in pyridine affords the potassium-free [Cl2(py)2Y{(µ3-NH)3Ti3(?5-C5Me5)3(µ3-N)}] (4) complex. Whereas the reaction of 3 with 1 equiv of 18-crown-6 leads to the molecular complex [(18-crown-6)K(µ-Cl)3Y{(µ3-NH)3Ti3(?5-C5Me5)3(µ3-N)}] (5), the analogous treatment of 3 with cryptand-222 affords the ion pair [K(crypt-222)][Cl3Y{(µ3-NH)3Ti3(?5-C5Me5)3(µ3-N)}] (6). The X-ray crystal structures of 4, 5, and 6 have been determined. Density functional theory (DFT) calculations have elucidated the electronic structure of these species, which should be regarded as containing trivalent Y bonded to the {(µ3-NH)3Ti3(?5-C5Me5)3(µ3-N)} metalloligand radical anion

Combined theoretical and mass spectrometry study of the formation-fragmentation of small polyoxomolybdates

We investigate the assembly of small polyoxomolybdates using Car-Parrinello molecular dynamics simulations which show that there is an expansion of the coordination sphere of the Mo center from four to six in molybdate anions when the acidity of the solution is increased. With the help of complementary static density functional theory (DFT) calculations and electrospray ionization mass spectrometry experiments, we are able to postulate tentative mechanisms, with energy-cascade profiles, for the formation of the Lindqvist Mo6O19](2)(-) anion. Similar to the family of isopolytungstates, it can be proposed that the Mo6O19](2)(-) is formed by the aggregation of one molybdenum unit at a time; however, significant differences with respect to isopolytungstates are also found. The different behavior of chromates with respect to molybdates and tungstates is also considered

Small endohedral metallofullerenes: Exploration of the structure and growth mechanism in the Ti@C2n (2n = 26-50) family

10.1039/c4sc02268hThe formation of the smallest fullerene, C28, was recently reported using gas phase experiments combined with high-resolution FT-ICR mass spectrometry. An internally located group IV metal stabilizes the highly strained non-IPR C28 cage by charge transfer (IPR = isolated pentagon rule). Ti@C44 also appeared as a prominent peak in the mass spectra, and U@C28 was demonstrated to form by a bottom-up growth mechanism. We report here a computational analysis using standard DFT calculations and Car-Parrinello MD simulations for the family of the titled compounds, aiming to identify the optimal cage for each endohedral fullerene and to unravel key aspects of the intriguing growth mechanisms of fullerenes. We show that all the optimal isomers from C26 to C50 are linked by a simple C2 insertion, with the exception of a few carbon cages that require an additional C2 rearrangement. The ingestion of a C2 unit is always an exergonic/exothermic process that can occur through a rather simple mechanism, with the most energetically demanding step corresponding to the closure of the carbon cage. The large formation abundance observed in mass spectra for Ti@C28 and Ti@C44 can be explained by the special electronic properties of these cages and their higher relative stabilities with respect to C2 reactivity. We further verify that extrusion of C atoms from an already closed fullerene is much more energetically demanding than forming the fullerene by a bottom-up mechanism. Independent of the formation mechanism, the present investigations strongly support that, among all the possible isomers, the most stable, smaller non-IPR carbon cages are formed, a conclusion that is also valid for medium and large cages. This journal i

Connecting theory with experiment to understand the initial nucleation steps of heteropolyoxometalate clusters

A complimentary combination of Density Functional Theory (DFT) methodology and Electrospray Ionization-Mass Spectrometry (ESI-MS) has been utilized to increase our limited understanding of the first nucleation steps in the formation of the [XM(12)O(40)](n-) Keggin polyoxometalates (POMs) (where addenda metal atom M = W or Mo, and the heteroatom X = P or As). We postulate that the first key steps of nucleation into discrete, high nuclearity heteropolyanions proceed via the formation of isodinuclear species (e. g. [M(2)O(7)](2-)), which undergo successive steps of protonation and water condensation to form a heterotrinuclear fragment, which acts as a template for the constituent parts required for subsequent aggregation and formation of the plenary Keggin heteropolyanion. The stability of calculated structures of the numerous postulated intermediates has been analysed and discussed in detail, and these results complemented using experimental mass spectrometry, using an assembly (reaction solution analysis) and disassembly (fragmentation of single crystals) approach. Overall, no significant differences between the Keggin POMs were found when changing the addenda metal atom (W or Mo) or the heteroatom (P or As); although small differences among the lowest-energy structures were detected