Assembly of multinuclear Ag complexes and Keggin polyoxometalates adjusted by organic ligands: syntheses, structures and luminescence

Abstract

Two unusual α-Keggin-based compounds with multinuclear silver clusters, {[Ag₇(H₂biim)₅][PW₁₁O₃₉]}·Cl·H₃O (1) and {[Ag₂(H₂biim)₂][Ag(phnz)](PW₁₂O₄₀)}·H₂O (2) (H₂biim = 2,2′-biimidazole, phnz = phenazine), have been hydrothermally synthesized and structurally characterized by elemental analyses, IR spectra, thermogravimetric analysis and X-ray crystallography. Compound 1 displays a 2D network featuring dimerized monolacunary Keggin anions {PW₁₁O₃₉}₂ which are connected together through pentanuclear silver clusters. Interestingly, besides {Ag₅}⁵⁺ clusters, there are another kinds of argentophilic {Ag₄}⁴⁺ clusters coexisting in compound 1. Compound 2 consists of four subunits: 1D cationic chains [Ag(phnz)]⁺, dinuclear silver-H₂biim units [Ag₂(H₂biim)₂]²⁺, discrete polyanions {PW₁₂O₄₀}³⁻ and water molecules, which are further joined by hydrogen bonds to form a 3D supramolecular structure. The differences in the structures of compounds 1 and 2 indicate that the introduction of the secondary organic ligand plays a key role in determining the final structure. The electrochemical, electrocatalytic behaviors and luminescent properties of compounds 1 and 2 have also been investigated.