What is the maximum charge uptake of Lindqvist-type polyoxovanadates in organic–inorganic heterostructures?

Abstract

One of the striking characteristics of the tris(alkoxo)-ligated Lindqvist-type polyoxovanadates [V^V₆O₁₃{(OCH₂)₃CR}₂]²⁻ in highest oxidation state in solution is the ease of their chemical post-functionalization via the R group. On surfaces it is their conductivity as a function of individual V(3d) redox states. In both cases, the structural stability of the fully-oxidized dianion is enabled by charge-balancing counterions. In this Article, we explore the charge stability and the charge distibution across the molecular Lindqvist-type hexavanadate structure regarding the R functionality (R = OC₂H₄N₃, CH₂N₃, and O₃C₂₉H₃₆N₅) and the different type of countercations (Cat = K⁺, Li⁺, NH₄⁺, H⁺, or Mg²⁺). We show that the hexavanadate core can accept in its vacant V(3d) orbitals at least four and, in some cases, up to nine additional electrons if the negative charge is offset by the corresponding cation(s), without electron leakage to the covalently attached R groups. Remarkably, the maximum number of accepted electrons strongly depends on the type of cation(s) and is independent on the type of the remote R group exploited herein. The (Cat)_n[V^V₆O₁₃{(OCH₂)₃CR}₂] complexes exibit the structural integrity in all studied charged states. Our study demonstrates the importance of the countercations of multistate polyoxovanadate nanoswitches for the development of multi-charge based molecular memories and/or batteries.