Unsaturated Heteropolyoxotungstates with Platinum Cation Complexation

Abstract

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 K 27 [KAsW 40 O 140 ] and for cation a solution of K 2 [PtCl 6 ]. 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, confi rmed 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 S 1-4 , which can coordinate metal cations, depending on the size of their cationic radius and the electronic charge they hold. Th ey are assemblies of polyhedra containing inside the X heteroatom (primary or secondary) and the M addenda atoms (transition metals, hexacoordinated). Th e structure is delimited by oxygen atoms, with low basicity, relatively inactive, which does not favor further polymerization. Th is is the key for stability of these compounds [1,2].Th e polyoxotungstates are a subdivision of this class, where the addenda atom M is represented by W. Basic element of structure is the WO 6 octahedron coordinated around the XO p heteroatoms (Figure 1a and 1b).Th ese compounds have saturated or unsaturated structures obtained by removing one or several WO 6 octahedrons. Th e unsaturated polyoxometalates are a special category of coordination compounds because of their physical and chemical properties, based on unsaturated structures [3]. Th e terminal oxygen atoms from their structures give them a high coordinative capacity for many cations [4,5]. After coordination, the structures do not change; only little displacements of atoms occur. Depending on the degree of unsaturated structures, in lacunae, a high density