Keggin-type polyoxometalate 1 : 1 complexes of Pb(ii) and Bi(iii): experimental, theoretical and luminescence studies

Abstract

Bi³⁺ and Pb²⁺ uptake by a monolacunary Keggin-type [PW₁₁O₃₉]⁷⁻ anion leads to the formation of [PW₁₁O₃₉Bi]⁴⁻ and [PW₁₁O₃₉Pb]⁵⁻ complexes with a stereochemically active lone pair at the incorporated heterometal. The two complexes were isolated as (TBA)₄[PW₁₁O₃₉Bi] (1) and (TBA)₅[PW₁₁O₃₉Pb] (2) and characterized by ³¹P and ¹⁸³W NMR spectroscopy, high-resolution electrospray mass-spectrometry (HR-ESI-MS) and cyclic voltammetry (CV). EXAFS and XANES data confirm the unchanged oxidation state and ψ-square pyramidal geometry of Bi³⁺ and Pb²⁺ in 1 and 2. DFT calculations were used in order to (i) confirm the absence of ligands attached to the heterometal sites in both complexes and localize the lone pair, and (ii) assign all signals in the ¹⁸³W NMR spectra. Complexes 1 and 2 demonstrate photoluminescence (PL). A reversible change in the PL spectra of both complexes in the presence of water vapor has been detected. On the contrary, PL data for sandwich-type ((CH₃)₄N)₄K₃[H₄(PW₁₁O₃₉)₂Bi]·25H₂O (3) do not show sensitivity to water vapor.