Tag Archives: polyoxometalates

The UV and IR Comparative Spectrophoto-metric Study of Some Saturated and Lacunary Polyoxometalates

DOI: 10.2478/amma-2014-0017

Objectives: The polyoxometalates are a class of inorganic compounds with controllable shapes and sizes, and with excellent properties that make them attractive for various applications. This study is aimed at the comparative UV and IR spectra of Keggin type polyoxometalates.
Methods: Compounds under (UV and IR) investigations were divided into several groups to highlight similarities between compounds or classes of compounds for the same category. There are four types of saturated Keggin structures and six lacunar compounds included in this study. The study begins with the UV investigations on aqueous solutions with 10-5 M concentration for these compounds. IR spectra were recorded as KBr pressed pellets.
Results: The UV spectras presents large strong peaks between 185–195 nm corresponding to W = Od bonds, between 251–268 nm for W-O-W bridge bonds, depending on heteroatom types (As, Sb). The unsaturated cryptand ligand having Co2+ coordinated presents the most intense peak, due to the involvement of oxygen atoms from terminal W = Od coordinative bonds with high electronic densities in coordination of W-O-Co bond. The IR spectra present many peaks that are associated as follows: for terminal bonds W = Od, 955–970 cm-1; for W-O-W bridging bonds, 790–910 cm-1; for W-O-As/Sb bonds to heteroatom, 690–760 cm-1. Vibrations of the bonds between heteroatoms and oxygen (As/Sb-O) appear around 620–660 cm-1.
Conclusions: Similarities appear from the recorded spectra, between compounds of the same class, by category association. Very fine displacements of peaks that occur explain the influence of heteroatoms, addenda atoms or coordinated cations.

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Unsaturated Heteropolyoxotungstates with Platinum Cation Complexation

DOI: 10.2478/amma-2014-0007


Background: Polyanions are a special category of coordination compounds with a large development in last years. By coordination of metal oxoions at the lacunary polyoxometalates are obtained new compounds which are studied for theirs possible antitumoral and antiviral activities. The polyoxometalates can bind cations by oxygen atoms from their saturated surface structure or by embedding in vacant sites.
Material and method: The methods used for determining cation coordination with the unsaturated polyoxotungstate are spectrophotometry and conductometry. The solutions used in this study were: for ligand a solution of K27[KAsW40O140] and for cation a solution of K2[PtCl6].
The variation of electrical conductivity of ionic species found in solution, caused by their concentrations, decreases during the complex formation, which was determined by conductometry. The spectrophotometric assay was performed to verify ratios between cation:ligand combination, determined by conductometry.
Results: The graphical representations of conductivity function of number of moles of added titrant solutions emphasize that there are two types of coordination compounds with two different combination ratios ligand:cation at 1:2 or 1:4. The spectrophotometric determination performed, confirmed these ratios.
Conclusions: There are two types of coordination complexes, and the ligand:cation ratios are well known for encrypting polyoxotungstates type used in the study. Besides the main active position SC where K+ alkaline cation is coordinated, it has four active stand side S1–4, which can coordinate metal cations, depending on the size of their cationic radius and the electronic charge they hold.

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