Three multi-nuclear clusters and one infinite chain induced by a pendant 4-butyl-1H-pyrazole ligand for modification of Keggin anions

Abstract

By utilizing pendant 4-butyl-1H-pyrazole (Hbpz) with an alkyl “tail” –(CH₂)₃CH₃, four Keggin-based complexes containing different transition metal multi-nuclear clusters and an infinite chain were hydrothermally synthesized and structurally characterized, [Cu^I₄(bpz)₄(pz)₂(H₆PW₁₁Cu^IIO₃₉)₂]·10H₂O (1), [Cu^II₂(bpz)₂(H₂O)₂(H₃PCu_0.5Mo_11.5O₄₀)]·3H₂O (2), [Ag₃(bpz)₂(pz)(H₄SiW₁₂O₄₀)]·4H₂O (3) and [Ag₅(bpz)₄(H_5/2PMo₁₂O₄₀)₂]·6H₂O (4) (pz = pyrazole). Compound 1 contains a tetra-nuclear cluster [Cu^I₄(bpz)₄(pz)₂]²⁻, in which four Cu^I ions are fixed by four bpz and two pz ligands. These clusters are linked by Keggin anion dimers to form a 2D layer. In compound 2, the ptz ligands fuse the Cu^II ions and an infinite 1D metal–organic chain is constructed with the Keggin anions hanging up and down covalently. Compound 3 has a planar triangle tri-nuclear cycle [Ag₃(bpz)₂(pz)] with three Ag^I as cores. These cycles build a 3D framework of 3 through the further linkages of Keggin anions and Ag–Ag bonds. In compound 4, there exist discrete [Ag₅(bpz)₄]⁺ clusters with four bpz ligands fused by five Ag^I cores, which are linked by Keggin anions alternately to form a 1D chain. Adjacent chains share the Ag–O bonds and a 2D layer is constructed. The bpz ligand is firstly introduced into the POM field and its successive two N donors are essential for the construction of multi-nuclear clusters and an infinite chain of 1–4. Additionally, the electrochemical and photocatalytic properties of the title compounds have been investigated.