Anion-dependent construction of copper(i/ii)-1,2,4,5-tetra(4-pyridyl)benzene frameworks

Abstract

The unique tetrapyridyl ligand 1,2,4,5-tetra(4-pyridyl)benzene (bztpy) isolated from previous hydrothermal in situ metal ligand reaction is found to exhibit remarkable anion-dependent assembly of a series of novel metal–organic frameworks (MOFs), [Cu₂(CN)₂(bztpy)] (1), [Cu(SO₄)(bztpy)]·1.5H₂O (2), [Cu₂Br₂(bztpy)]·MeCN (3) and [Cu₁₀I₁₀(bztpy)₂]·2H₂O (4), which were synthesized under hydro/solvothermal conditions. These MOFs were characterized by elemental analysis, IR and single-crystal X-ray diffraction. Compound 1 consists of [Cu(CN)]_n chains that link the neighbouring ones via tetradentate bztpy bridges to form a corrugated 2D layer. When bztpy is treated with CuSO₄, a 3D (3,5)-connected network 2 is obtained, in which novel [Cu(bztpy)]_n ladders are interconnected by sulfate anions μ-bridges. However, Br⁻ and I⁻ anions assist the formation of {Cu₂Br₂} and {Cu₁₀I₁₀} SBU in the cluster-based metal–organic frameworks 3 and 4, respectively, and result in a completely different topology. Compound 3 shows a 3D PtS net, while compound 4 has a new 3D (4,8)-connected topology. A discussion of the crystal structures, as well as the coordination behaviour of the special tetrapyridyl ligand upon different geometries of the central connecter is provided. In addition, the photoluminescent properties of 1, 3 and 4 in the solid state at ambient temperature are also investigated.