Ion-pairs of structurally related polyoxotantalate clusters and divalent metal cations

Abstract

We report cation-binding behaviors of two {P₄Ta₆}-type polyoxometalate (POM) clusters with cis- and trans- subunit geometry in aqueous solution. Two types of divalent cations, Sr²⁺ and Pb²⁺, possess different binding affinities and sites when interacting with {P₄Ta₆}. Sr²⁺ ions only form solvent-share ion-pairs with {P₄Ta₆}, whereas Pb²⁺ ions form contact-ion pairs, selectively interacting with the phosphate groups at different locations and subsequently induce the aggregation of {P₄Ta₆}, confirmed by isothermal titration calorimetry (ITC), NMR, and small-angle X-ray scattering (SAXS) techniques. Despite Sr²⁺ and Pb²⁺ possessing similar ionic sizes and hydration energies, Pb²⁺ ions with stronger coordination capability result in a closer association with the clusters, eventually to selective interaction that depends on the chelating effect, charge density, and the acidity of phosphate groups at specific sites.

Graphical Abstract

Keywords:

• Ion-pair
• polyoxotantalates
• isomerism
• polyoxometalates

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

T.L. acknowledges support by NSF (CHE1904397) and the University of Akron. D. Zhang thanks financial support from the NSFC (21601056) and the Program for Science & Technology Innovation Talents in Universities of Henan Province (19HASTIT044). NSF’s ChemMatCARS Sector 15 is supported by the Divisions of Chemistry (CHE) and Materials Research (DMR), National Science Foundation, under grant number NSF/CHE- 1834750. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357.