PubMed · 5628292
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Y Sugiura. 1967. [Dielectric dispersion].. https://pubmed.ncbi.nlm.nih.gov/5628292/
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Polyoxometalates have been traditionally the subject of study of molecular inorganic chemistry. Yet, these polynuclear molecules, reminiscent of oxide clusters, present a wide range of structures and with them ideal frameworks for the deployment of a plethora of useful magnetic, electroionic, catalytic, bioactive and photochemical properties. With this in mind, a new trend towards the application of these remarkable species in materials science is beginning to develop. In this review we analyze this trend and discuss two main lines of thought for the application of polyoxometalates as materials. On the one hand, there is their use as clusters with inherently useful properties on themselves, a line which has produced fundamental studies of their magnetic, electronic or photoelectrochemical properties and has shown these clusters as models for quantum-sized oxides. On the other hand, the encapsulation or integration of polyoxometalates into organic, polymeric or inorganic matrices or substrates opens a whole new field within the area of hybrid materials for harnessing the multifunctional properties of these versatile species in a wide variety of applications, ranging from catalysis to energy storage to biomedicine.
The parallel-mode electron paramagnetic resonance (EPR) spectrum of the S(1) state of the oxygen-evolving complex (OEC) shows a multiline signal centered around g=12, indicating an integer spin system. The series of [Mn(2)(2-OHsalpn)(2)] complexes were structurally characterized in four oxidation levels (Mn(II)(2), Mn(II)Mn(III), Mn(III)(2), and Mn(III)Mn(IV)). By using bulk electrolysis, the [Mn(III)Mn(IV)(2-OHsalpn)(2)(OH)] is oxidized to a species that contains Mn(IV) oxidation state as detected by X-ray absorption near edge spectroscopy (XANES) and that can be formulated as Mn(IV)(4) tetramer. The parallel-mode EPR spectrum of this multinuclear Mn(IV)(4) complex shows 18 well-resolved hyperfine lines center around g=11 with an average hyperfine splitting of 36 G. This EPR spectrum is very similar to that found in the S(1) state of the OEC. This is the first synthetic manganese model complex that shows an S(1)-like multiline spectrum in parallel-mode EPR.
Detection of lead and mercury by attenuated total internal reflectance spectroscopy coupled to stripping voltammetry is demonstrated. Changes in attenuation of light passing through an indium tin oxide optically transparent electrode (ITO-OTE) accompany the electrodeposition and stripping of lead and mercury on the electrode surface. The change in absorbance during stripping of electrodeposited metal constitutes the analytical response that enables detection over a range of 2.5 x 10(-7)-5 x 10(-5) and 5 x 10(-8)-5 x 10(-5) M for mercury and lead, respectively. The spectroelectrochemical responses of mercury and lead on the ITO surface are characterized and optimized with respect to solution conditions, the potential excitation signals used for deposition and stripping, and wavelength for detection. The deposited metals were examined by environmental scanning electron miscroscopy, and the electrodeposition pattern of lead and mercury was found to influence the optical response.