Central-metal exchange, improved catalytic activity, photoluminescence properties of a new family of d10 coordination polymers based on the 5,5′-(1H-2,3,5-triazole-1,4-diyl)diisophthalic acid ligand

Abstract

The rigid and planar tetracarboxylic acid 5,5′-(1H-2,3,5-triazole-1,4-diyl)diisophthalic acid (H₄L), incorporating a triazole group, has been used with no or different pyridine-based linkers to construct a family of d¹⁰ coordination polymers, namely, {[H₂N(CH₃)₂]₃[Cd₃(L)₂(HCOO)]}_n (1), {[Cd₂(L)(py)₆]·H₂O}_n (2), {[H₂N(CH₃)₂] [Cd₂(L)(HCOO)(H₂O)₄]}_n (3), {[Zn(H₂L)]·H₂O}_n (4), and {[Zn(H₂L)(4,4′-bipy)_0.5]·C₂H₅OH·H₂O}_n (5) (py = pyridine, 4,4′-bipy = 4,4′-bipyridine). 1 constructs a 3D porous network containing two kinds of channels: one is filled with coordinated HCOO⁻ anions, and the other with [H₂N(CH₃)₂]⁺ cations. The framework of 1 can be described as a rare (5,6,7)-connected net with the Schläfli symbol of (4¹²·5·6²)(4⁵·5³·6²)₂(4⁸·5³·6⁸·8²)₂. The Cd(II) ions in 2 are connected through the carboxylate ligands to form a 2D layer, with aperture dimensions of ∼15.1 Å × 16.2 Å. The network of 3 features a 3D (3,4)-connected (6·8·10)₂(6·8³·10²) topology. A 3D network with the (4²·6·8³) topology of 4 possesses an open 1D channel with the free volume of 29.2%. 5 is a 2D layer structure with the (4²·6³·8)(4²·6) topology. The fluorescence lifetime τ values of 1–5 are on the nanosecond timescale at room temperature. In particular, central-metal exchange in 2 leads to a series of isostructural M(II)–Cd frameworks [M = Cu (2a), Co (2b), Ni (2c)] showing improved catalytic activity for the synthesis of 1,4,5,6-tetrahydropyrimidine derivatives. Based on this, a plausible mechanism for the catalytic reaction has been proposed and the reactivity–structure relationship has been further clarified.