Exploiting the linking propensity of a water encapsulated POV cluster anion [As₆V₁₅O₄₂(H₂O)]^6- towards lanthanide cations: syntheses, crystal structures and thermal properties of [{M(H₂O)₇}₂(As₆V₁₅O₄₂(H₂O)]·xH₂O (M = La³⁺, Sm³⁺ and Ce³⁺; x = 12, 13 and 11, respectively)

Abstract

The polyoxovanadate cluster anion [As₆V₁₅O₄₂(H₂O)]^6-, an well known magnetic object, has been reacted with lanthanide ions (namely La³⁺, Sm³⁺ and Ce³⁺ ions) in a controlled synthesis resulting in the formation of a new series of coordination polymers [{La(H₂O)₇}₂As₆V₁₅O₄₂(H₂O)]·12H₂O (2), [{Sm(H₂O)₇}₂As₆V₁₅O₄₂(H₂O)]·13H₂O (3) and [{Ce(H₂O)₇}₂ As₆V₁₅O₄₂(H₂O)]·11H₂O (4). In compounds 2, 3 and 4, the high nuclearity spin cluster [As₆V₁₅O₄₂(H₂O)]^6- acts as a tetradentate ligand with terminal oxo groups (V=O) as donor centers. Compounds 2-4 are characterized by elemental and routine spectroscopic analyses and finally by single crystal X-ray structure determination. Compounds 2-4 are isomorphous in which each {V15} cluster anion is coordinated to four Ln³⁺ ion through its terminal oxygen atoms and each Ln³⁺ ion is coordinated to two cluster anions and seven water molecules satisfying the coordination number of nine around a lanthanide cation. In the crystal structure, the non-coordinated (lattice) water molecules, lanthanum-coordinated water molecules and V=O_t oxygen atoms (O_t = terminal oxygen) are involved in O-H···O hydrogen bonding interactions. The hydrogen bonding distances are measured as O···O separations, since hydrogen atoms could not be located in the crystal structures. The hydrogen bonding distances are varied in the range of 2.640-3.000 Å. The title compounds are additionally characterized by thermogravimetric analysis.