Inorganics, Volume 4, Issue 2 (June 2016) – 13 articles

The reaction of the lithium tris(2-pyridyl)stannate [LiSn(2-py^6OtBu)₃] (py^6OtBu = C₅H₃N-6-OtBu), 1, with the element(II) amides E{N(SiMe₃)₂}₂ (E = Sn, Pb) afforded complexes [LiE{Sn(2-py^6OtBu)₃}₃] for E = Sn (2) and E = Pb (3), which reveal three Sn–E bonds each. Compounds 2 and 3 have been characterized by solution NMR spectroscopy and X-ray crystallographic studies. Large ¹J(¹¹⁹Sn–^119/117Sn) as well as ¹J(²⁰⁷Pb–^119/117Sn) coupling constants confirm their structural integrity in solution. However, contrary to 2, complex 3 slowly disintegrates in solution to give elemental lead and the hexaheteroarylditin [Sn(2-py^6OtBu)₃]₂ (4). Full article

The dynamic behavior of tetrapropylammonium (TPA) cations in the clear precursor sols for silicalite synthesis has been investigated by ¹H diffusion ordered spectroscopy (DOSY), T₁, T₂, and T_1ρ ¹H relaxation, as well as ¹H→¹³C cross polarization (CP) nuclear magnetic resonance. The DOSY NMR experiments showed the presence of strong solute–solvent interactions in concentrated sols, which are decreasing upon dilution. Similarities in dependence of diffusion coefficients with fractional power of the viscosity constant observed for nanoparticles, TPA cations and water led to the conclusion that they aggregate as anisotropic silicate-TPA particles. Relaxation studies as well as ¹H→¹³C CP experiments provide information on dynamic properties of ethanol, water and TPA cations, which are function of silicate aggregates. The general tendency showed that the presence of silicate as oligomers and particles decreases the relaxation times, in particular T₂ and T_1ρH, as a consequence of involvement of these latter in ion-pairing interactions with water-solvated TPA molecules slowing down their mobility. Furthermore, from the ¹H→¹³C CP dynamics curve profiles a change in the CP transfer regime was observed from fast (T_CH << T_1ρH) for solutions without silicates to moderate (T_CH~T_1ρH) when silicates are interacting with the TPA cations that may reflect the occlusion of TPA into flexible silicate hydrate aggregates. Full article

Blended cathode materials made by mixing LiFePO₄ (LFP) with LiMnPO₄ (LMP) or LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) that exhibit either high specific energy and high rate capability were investigated. The layered blend LMP–LFP and the physically mixed blend NMC–LFP are evaluated in terms of particle morphology and electrochemical performance. Results indicate that the LMP–LFP (66:33) blend has a better discharge rate than the LiMn_1−yFe_yPO₄ with the same composition (y = 0.33), and NMC–LFP (70:30) delivers a remarkable stable capacity over 125 cycles. Finally, in situ voltage measurement methods were applied for the evaluation of the phase evolution of blended cathodes and gradual changes in cell behavior upon cycling. We also discuss through these examples the promising development of blends as future electrodes for new generations of Li-ion batteries. Full article

We have successfully synthesized K₁₇{[{KIn₂(μ-OH)₂}(α,α-Si₂W₁₈O₆₆)]₂[In₆(μ-OH)₁₃(H₂O)₈]}·35H₂O (potassium salt of In₁₀-open), an open-Wells–Dawson polyoxometalate (POM) containing ten indium metal atoms. This novel compound was characterized by X-ray crystallography, ²⁹Si NMR, FTIR, complete elemental analysis, and TG/DTA. X-ray crystallography results for {[{KIn₂(μ-OH)₂}(α,α-Si₂W₁₈O₆₆)]₂[In₆(μ-OH)₁₃(H₂O)₈]}¹⁷⁻ (In₁₀-open) revealed two open-Wells–Dawson units containing two In³⁺ ions and a K⁺ ion, [{KIn₂(μ-OH)₂}(α,α-Si₂W₁₈O₆₆)]¹¹⁻, connected by an In₆-hydroxide cluster moiety, [In₆(μ-OH)₁₃(H₂O)₈]⁵⁺. In₁₀-open is the first example of an open-Wells–Dawson POM containing a fifth-period element. Moreover, to the best of our knowledge, it exhibits the highest nuclearity among the indium-containing POMs reported to date. Full article

The β,β-isomer of open-Wells–Dawson polyoxometalate (POM) containing a tetra-iron(III) cluster, K₉[{Fe₄(H₂O)(OH)₅}(β,β-Si₂W₁₈O₆₆)]·17H₂O (potassium salt of β,β-Fe₄-open), was synthesized by reacting Na₉H[A-β-SiW₉O₃₄]·23H₂O with FeCl₃·6H₂O at pH 3, and characterized by X-ray crystallography, FTIR, elemental analysis, TG/DTA, UV–Vis, and cyclic voltammetry. X-ray crystallography revealed that the {Fe³⁺₄(H₂O)(OH)₅}⁷⁺ cluster was included in the open pocket of the β,β-type open-Wells–Dawson polyanion [β,β-Si₂W₁₈O₆₆]¹⁶⁻ formed by the fusion of two trilacunary β-Keggin POMs, [A-β-SiW₉O₃₄]¹⁰⁻, via two W–O–W bonds. The β,β-open-Wells–Dawson polyanion corresponds to an open structure of the standard γ-Wells–Dawson POM. β,β-Fe₄-open is the first example of the compound containing a geometrical isomer of α,α-open-Wells–Dawson structural POM. Full article

New organophosphonate derivatives of monovacant Keggin-type polyoxotungstates that contain naphthyl groups have been synthesized and characterized in both solid state and solution. Single-crystal structural analysis shows that two phosphonate groups occupy the vacant position of the lacunary cluster unit in the isostructural compounds [N(C₄H₉)₄]₃[H(POC₁₁H₉)₂(α-HBW₁₁O₃₉)] (TBA-1) and [N(C₄H₉)₄]₃[H(POC₁₁H₉)₂(α-SiW₁₁O₃₉)] (TBA-2). Liquid-solution UV–Vis transmittance and solid-state diffuse reflectance spectroscopy studies reveal the presence of a new absorption band in the visible region, the charge transfer character of which has been further confirmed by time-dependent density functional theory (TD-DFT) calculations. The latter evidence that the charge transfer process is dominated by transitions from the highest occupied molecular orbital (HOMO), localized in the aromatic ring of the organic group, to the lowest unoccupied molecular orbital (LUMO), localized in the Keggin anion. Photoluminescence studies show that the fluorescent properties of the 1-naphthylmethylphosphonate group are quenched upon its incorporation into the inorganic oxo-tungstate skeleton. The solution stability of the hybrid clusters has been evaluated by a combination of ¹H-, ¹³C- and ³¹P-Nuclear Magnetic Resonance spectroscopy and Electrospray Ionization-Mass Spectrometry. The hybrid polyanion [H(POC₁₁H₉)₂(α-HBW₁₁O₃₉)]³⁻ (1) herein constitutes the first structurally characterized organo-p-block containing borotungstate, and hence it confirms that this strategy for the organic functionalization of polyoxometalate clusters can be applied to new platforms belonging to the family of group-13 heteropolyoxotungstates. Full article

An overview of the synthesis, characterization and catalytic applications of polyoxometalates/zeolites composites is given. The solids obtained by direct synthesis of the polyoxometalate in the presence of the zeolite are first described with their applications in catalysis. Those obtained by a direct mixing of the two components are then reviewed. In all cases, special care is taken in the localization of the polyoxometalate, inside the zeolite crystal, in mesopores or at the external surface of the crystals, as deduced from the characterization methods. Full article

Some hemoproteins have the structural robustness to withstand extraction of the heme cofactor and replacement with a heme analog. Recent reports have reignited interest and exploration in this field by demonstrating the versatility of these systems. Heme binding proteins can be utilized as protein scaffolds to support heme analogs that can facilitate new reactivity by noncovalent bonding at the heme-binding site utilizing the proximal ligand for support. These substituted hemoproteins have the capability to enhance catalytic reactivity and functionality comparatively to their native forms. This review will focus on progress and recent advances of artificially engineered hemoproteins utilized as a new target for the development of biocatalysts. Full article

Many paint, ink and coating formulations contain alkyd-based resins which cure via autoxidation mechanisms. Whilst cobalt-soaps have been used for many decades, there is a continuing and accelerating desire by paint companies to develop alternatives for the cobalt soaps, due to likely classification as carcinogens under the REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) legislation. Alternative driers, for example manganese and iron soaps, have been applied for this purpose. However, relatively poor curing capabilities make it necessary to increase the level of metal salts to such a level that often coloring of the paint formulation occurs. More recent developments include the application of manganese and iron complexes with a variety of organic ligands. This review will discuss the chemistry of alkyd resin curing, the applications and reactions of cobalt-soaps as curing agents, and, subsequently, the paint drying aspects and mechanisms of (model) alkyd curing using manganese and iron catalysts. Full article

The adsorption of water on solid surfaces is a scientific evergreen which again recently prompted considerable attention in the materials, nano-, and surface science communities, respectively, due to conflicting evidence presented in the most highly regarded scientific journals. This mini review is a brief and personal perspective of the current literature (and our own data) about water adsorption for two examples, namely graphene and silicatene, which are both two-dimensional (2D) crystals. Silicatene, an inorganic companion of graphene, is intriguing as it presents us with the possibility to synthesize a 2D analog to zeolites by doping this crystalline silicon film. The wettability by water and whether or not support effects of epitaxial 2D crystals are present is of concern. Regarding applications: some 2D crystals appear promising for the hydrogen evolution reaction, i.e., hydrogen generation from water; a functionalization of graphene (by oxygen/water) to graphene oxide may be interesting for metal-free catalysis; the latest highlight in this field appears to be “icephobicity”, an application related to the hydrophobicity of surfaces. Full article

Silica monoliths featuring either mesopores or flow-through macropores and mesopores in their skeleton are prepared by combining spinodal phase separation and sol-gel condensation. The macroporous network is first generated by phase separation in acidic medium in the presence of polyethyleneoxides while mesoporosity is engineered in a second step in alkaline medium, possibly in the presence of alkylammonium cations as surfactants. The mesoporous monoliths, also referred as aerogels, are obtained in the presence of alkylpolyethylene oxides in acidic medium without the use of supercritical drying. The impact of the experimental conditions on pore architecture of the monoliths regarding the shape, the ordering, the size and the connectivity of the mesopores is comprehensively discussed based on a critical appraisal of the different models used for textural analysis. Full article

In the context of our systematic investigations of penta- and hexacoordinate silicon compounds, which included dianionic tri- (O,N,O′; O,N,N′) and tetradentate (O,N,N,O; O,N,N′,O′) chelators, we have now explored silicon coordination chemistry with a dianionic tetradentate (N,N′,N′,N) chelator. The ligand [o-phenylene-bis(pyrrole-2-carbaldimine), H₂L] was obtained by condensation of o-phenylenediamine and pyrrole-2-carbaldehyde and subsequently silylated with chlorotrimethylsilane/triethylamine. Transsilylation of this ligand precursor (Me₃Si)₂L with chlorosilanes SiCl₄, PhSiCl₃, Ph₂SiCl₂, (Anis)₂SiCl₂ and (4-Me₂N-C₆H₄)PhSiCl₂ afforded the hexacoordinate Si complexes LSiCl₂, LSiPhCl, LSiPh₂, LSi(Anis)₂ and LSiPh(4-Me₂N-C₆H₄), respectively (Anis = anisyl = 4-methoxyphenyl). ²⁹Si NMR spectroscopy and, for LSiPh₂, LSi(Anis)₂ and LSiPh(4-Me₂N-C₆H₄), single-crystal X-ray diffraction confirm hexacoordination of the Si atoms. The molecular structures of LSiCl₂ and LSiPhCl were elucidated by computational methods. Despite the two different N donor sites (pyrrole N, X-type donor; imine N, L-type donor), charge delocalization within the ligand backbone results in compounds with four similar Si–N bonds. Charge distribution within the whole molecules was analyzed by calculating the Natural Charges (NCs). Although these five compounds carry electronically different monodentate substituents, their constituents reveal rather narrow ranges of their charges (Si atoms: +2.10–+2.22; monodentate substituents: −0.54–−0.56; L²⁻: −1.02–−1.11). Full article

Electrical and magnetic properties are dominated by the (de)localization and the anisotropy in the distribution of unpaired electrons in solids. In molecular materials, these properties have been indirectly controlled through crystal structures using various chemical modifications to affect molecular structures and arrangements. In the molecular crystals, since the energy band structures can be semi-quantitatively known using band calculations and solid state spectra, one can anticipate the (de)localization of unpaired electrons in particular bands/levels, as well as interactions with other electrons. Thus, direct control of anisotropy and localization of unpaired electrons by locating them in selected energy bands/levels would realize more efficient control of electrical and magnetic properties. In this work, it has been found that the unpaired electrons on Cu(II)-complex anions can be optically controlled to behave as anisotropically-delocalized electrons (under dark) or isotropically-localized electrons like free electrons (under UV), the latter of which has hardly been observed in the ground states of Cu(II)-complexes by any chemical modifications. Although the compounds examined in this work did not switch between conductors and magnets, these findings indicate that optical excitation in the [Cu(dmit)₂]²⁻ salts should be an effective method to control spin distribution and anisotropy. Full article