Modelling local structural and electronic consequences of proton and hydrogen-atom uptake in VO2 with polyoxovanadate clusters.

We report the synthesis and characterisation of a series of siloxide-functionalised polyoxovanadate-alkoxide (POV-alkoxide) clusters, [V6O6(OSiMe3)(OMe)12] n (n = 1-, 2-), that serve as molecular models for proton and hydrogen-atom uptake in vanadium dioxide, respectively. Installation of a siloxide moiety on the surface of the Lindqvist core was accomplished via addition of trimethylsilyl trifluoromethylsulfonate to the fully-oxygenated cluster [V6O7(OMe)12]2-. Characterisation of [V6O6(OSiMe3)(OMe)12]1- by X-ray photoelectron spectroscopy reveals that the incorporation of the siloxide group does not result in charge separation within the hexavanadate assembly, an observation that contrasts directly with the behavior of clusters bearing substitutional dopants. The reduced assembly, [V6O6(OSiMe3)(OMe)12]2-, provides an isoelectronic model for H-doped VO2, with a vanadium(iii) ion embedded within the cluster core. Notably, structural analysis of [V6O6(OSiMe3)(OMe)12]2- reveals bond perturbations at the siloxide-functionalised vanadium centre that resemble those invoked upon H-atom uptake in VO2 through ab initio calculations. Our results offer atomically precise insight into the local structural and electronic consequences of the installation of hydrogen-atom-like dopants in VO2, and challenge current perspectives of the operative mechanism of electron-proton co-doping in these materials.

Heterometallic trinuclear oxo-centered clusters as single-source precursors for synthesis of stoichiometric monodisperse transition metal ferrite nanocrystals.

The use of heterobimetallic metal complexes as molecular single-source precursors is a promising strategy for the targeted synthesis of phase-pure stoichiometric ternary metal oxide nanocrystals. However, the design and synthesis of these precursors is not trivial and can require considerable effort. Using spinel metal ferrite nanocrystals of formula MFe2O4 (M = Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) as a model system, this paper evaluates the efficacy of the single-source precursor approach by comparing directly nanocrystals synthesized from the solvothermal reaction of heterobimetallic trinuclear oxo-bridged clusters of formula MIIFeIII2(µ3-O)(µ2-O2CR)6(H2O)3, R = CF3 to nanocrystals synthesized from the solvothermal reaction of stoichiometric mixtures of multi-source precursors, such as metal acetate or nitrate salts. For each M explored here, the clusters form phase-pure MFe2O4 nanocrystals with significantly narrower size distributions than nanocrystals synthesized from multi-source-precursors. In the case of M = Cu, the multi-source metal salt precursors produce a mixture of CuO and CuFe2O4. Additionally, changing the electronic nature of the R-group on the bridging carboxylate ligand from electron withdrawing (CF3) to electron donating (CH3 or C(CH3)3) decreases the average diameter of the resulting nanocrystals by a factor of two. The cluster molecules therefore offer superior control over both morphology and composition for transition metal ferrite nanocrystals. We hypothesize that this remarkable performance arises from the presence of pre-formed M2+-O-Fe3+ moieties in the cluster molecules that enable direct nucleation of MFe2O4 and preclude nucleation of binary oxide impurities.

Thermo-therapeutic applications of chitosan- and PEG-coated NiFe2O4 nanoparticles.

The paper reports the thermo-therapeutic applications of chitosan- and PEG-coated nickel ferrite (NiFe2O4) nanoparticles. In this study NiFe2O4 nanoparticles were synthesized by the co-precipitation method, tuning the particle size through heat treatment in the temperature range from 200-800 °C for 3 h. XRD and TEM analysis revealed that the the ultrafine nanoparticles were of size 2-58 nm. Crystallinity of the NiFe2O4 nanoparticles in the as-dried condition with the particle size ∼2-3 nm was confirmed from the presence of a lattice fringe in the HRTEM image. VSM measurements showed that a superparamagnetic/ferromagnetic transition occurs with increasing particle size, which was further confirmed by Mössbauer spectroscopy. The nickel ferrite nanoparticles with optimum particle size of 10 nm were then coated with materials commonly used for biomedical applications, i.e. chitosan and PEG, to form homogeneous suspensions. The hydrodynamic diameter and the polydispersity index (PDI) were analyzed by dynamic light scattering at the physiological temperature of 37 °C and found to be 187 nm and 0.21 for chitosan-coated nanoparticles and 285 nm and 0.32 for PEG-coated ones. The specific loss power of rf induction heating by the set-up for hyperthermia and r 2 relaxivity by the nuclear magnetic resonance were determined. The results of induction heating measurements showed that the temperature attained by the nanoparticles of size 10 nm and concentration of about 20 mg ml(-1) was >70 °C (for chitosan) and >64 °C (for PEG). It has been demonstrated that the required temperature for hyperthermia heating could be tuned by tuning the particle size, shape and magnetization and the concentration of solution. For other potential biomedical applications of the NiFe2O4 nanoparticle solution, e.g. magnetic resonance imaging, the NMR studies yielded the T 1 and T 2 relaxivities as 0.348 and 89 mM(-1) s(-1) respectively. The fact that the T 2 relaxivity is orders of magnitude higher than T 1 indicates that this is suitable as a T 2 contrast agent for magnetic resonance imaging.