Syntheses, structures and physical properties of transition metal–organic frameworks assembled from trigonal heterofunctional ligands

Abstract

Six novel metal–organic frameworks (MOFs), {Mn(bpydb)(bpyHdbH)}_n (1) {[Co₂(bpydb)₂](H₂O)_0.5}_n (2), {[Ni_0.5(bpydbH)(H₂O)](DMF)₂}_n (3), {[Cu₂(bpydb)₂](H₂O)_0.5}_n (4), {Zn(bpyHdb)₂}_n (5) and {[Cd_0.5(bpydb)_0.5(DMF)](H₂O)}_n (6), were successfully synthesized by assembling transition metal salts with trigonal heterofunctional ligand 4,4′-(4,4′-bipyridine-2,6-diyl) dibenzoic acid (bpydbH₂) under hydrothermal and/or solvothermal conditions. Compound 1 features a rare 4-fold interpenetrating (3,5)-connected framework with hms-type topology. Isostructural compounds 2 and 4, constructed by M₂(COO)₄ secondary building units, exhibit a robust 3D framework with alb topological type in 2-fold interpenetrating mode. Compound 3 consists of 2D (4,4) networks, which are further assembled into the new topological framework with the symbol (5³·6²·8)(5³·6³)₂ through O–H⋯O interactions. Compound 5 manifests a novel 4-connected interpenetrating framework, constructed by 2D (4,4) layers and interbedded N–H⋯O interactions. Non-interpenetrating honeycomb networks are observed in compound 6, and further packed into a 3D framework featuring 1D channels. The magnetic susceptibility of compound 2 indicates antiferromagnetic interactions between cobalt ions. The photoluminescent properties of 5 and 6 were investigated in the solid state at room temperature.