Intramolecular Re & BULL;& BULL;& BULL;O Nonvalent Interactions as a Stabilizer of the Polyoxorhenate(VII)

The first polyoxorhenate(VII) compound, pyrazolium polyoxorhenate((C4N2H5)(2)Re4O15), and two new rhenium(VII) and technetium(VII) saltshave been synthesized and studied. The structure of Tc2O7 has been reinvestigated. The [Re4O15](2-) polyoxoanion contains four Re(VII) atoms: onewith an octahedral environment and three with a tetrahedral environment.Polyoxorhenate is formed in the presence of a buffering agent, pyrazole,the latter maintaining pH = 2.5 during the formation of crystals.The [Re4O15](2-) polyoxoanionhas novel stoichiometry and the cis-conformation,likely due to the stabilizing intramolecular nonvalence interactions.For the first time, intramolecular interactions of the Re & BULL;& BULL;& BULL;O,Re & BULL;& BULL;& BULL;& mu;-O, and O & BULL;& BULL;& BULL;O are described(previously known were only intermolecular ones). In all of the compounds,intermolecular Re & BULL;& BULL;& BULL;O interactions are observed, which,however, in other compounds, do not lead to the formation of polyoxometalates.The Hirshfeld surface analysis showed that the main contribution tointermolecular interactions is made by the O & BULL;& BULL;& BULL;H/H & BULL;& BULL;& BULL;Ocontacts, van der Waals interactions of the H & BULL;& BULL;& BULL;H forcations, and the O & BULL;& BULL;& BULL;O for anions. DFT calculationsof the [Re4O15](2-) geometry,compared with the crystallographic data, revealed a deviation in theangles. Mass spectroscopy of the red polyoxometalate [Tc20O68](4-) was carried out for the firsttime. Comparison of the results of MALDI and LI for the first knownpolyoxometalates of the manganese subgroup made it possible to findgeneral patterns of oligomerization for rhenium and technetium compounds.The ESI-MS and LI-MS methods applied to solution and crystals Re compoundsmade it possible to prove rhenium being able to form not only [Re4O15](2-) but also heavier polyoxoanions. The [Re4O15](2-) wassynthesized from aqueous solutions at pH 2.5 and characterized bySCXRD. The discovered new type of intramolecular nonvalence interactionstabilizes the cis-polyrhenate. The MALDI methodproved the formation of heavier polyoxorhenates in aqueous solutionsof pyrazolium.