Coordination polymers of a multipyridyl and pyrazolyl ligand with conformational flexibility: syntheses, structures and luminescence

Abstract

In this work, we designed and synthesized a novel ligand, N,N-bis(6-(1H-pyrazolyl)2-pyridyl)-N′,N′-bis(4-pyridyl)1,4-phenylenediamine (L). Coordination of d¹⁰ metals, Co(II) and Cu(II), with L generated eight novel coordination polymers [ZnLCl₂]_n (1), [ZnLBr₂]_n (2), [ZnLI₂]_n (3), [CdL₂Cl₂]_n (4), [CdL₂Br₂]_n (5), [CdLI₂]_n (6), {[CoL(SCN)](ClO₄)}_n·1.5nDMF·0.5nH₂O (7) and {[Cu₂L₂(N₃)]·3ClO₄}_n (8). Single-crystal X-ray diffraction analyses revealed that complexes 1–3 and 6 are isostructural. In these complexes, the ligand L utilizes its two pyridyl nitrogens of the 4,4′-dpa moiety to bridge metal ions, affording 1D zigzag chains, which are further linked by intermolecular C–H⋯π and hydrogen bond interactions to form 3D supramolecular structures. Complexes 4 and 5 have isostructural 1D double chain structures. In the d¹⁰ metal complexes 1–6, the potentially chelating bppa units of L are left non-coordinated in the “L” or “M” shaped conformation. In contrast, in complexes 7 and 8, the bppa units chelate the paramagnetic metal ions in the “U” shaped conformation. For complex 7, the bppa unit of L chelates a Co(II) atom, and a pyridyl nitrogen of the 4,4′-dpa unit bridges another Co(II) atom, thus affording a 1D chain structure. Similar to that observed in 7, each L ligand in complex 8 links two Cu(II) ions, and a μ_1,3-azide further bridges two Cu(II) ions from neighbouring chains, affording a 2D undulated layer, which is interpenetrated by another such 2D sheet, forming a 2-fold interpenetrated structure. Based on the interesting structural results, the solid-state luminescent properties of complexes 1–6 were investigated, which revealed that the emission maximum wavelengths can be tuned in a large range of 372–486 nm.