Hydrothermal preparation, crystal structures and properties of novel Mn(ii) metal–organic frameworks with 5-nitro-1,2,3-benzenetricarboxylate and various dipyridyl ligands

Abstract

Five Mn(II) coordination polymers, [Mn_3.5(O₂N-btb)₂(O₂N–Hbtb)_0.5(2,2′-bipy)₂(H₂O)₄]·1.5H₂O (1), [Mn₃(O₂N-btb)₂(4,4′-bipy)₃(H₂O)₂]·2H₂O (2), [Mn₃(O₂N-btb)₂(bpe)(H₂O)₈]·bpe(3), [Mn₃(O₂N-btb)₂(bpa)(H₂O)₅]·0.5bpa H₂O (4) and [Mn₃(O₂N-btb)₂(bpp)₂(H₂O)₄] (5), were prepared by hydrothermal reactions of Mn(II) acetate with O₂N–H₃btb (O₂N–H₃btb = 5-nitro-1,2,3-benzenetricarboxylic acid) in the presence of different dipyridyl co-ligands (2,2′-bipy = 2,2′-bipyridyl, 4,4′-bipy = 4,4′-bipyridyl, bpe = 1,2-bi(4-pyridyl)ethene, bpa = 1,2-bi(4-pyridyl)ethane and bpp = 1,3-di(4-pyridyl)propane). Their crystal structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra and TG analyses. Complex 1 shows a 3D (3,5)-connected coordination framework with (4²·5)(4·12²)(4·5·7)₂(4²·5·6·7·9·12³·13) topology. Notably, the μ₇-bridging mode of O₂N-btb in 1 has never been found in coordination complexes with 1,2,3-benzenetricarboxylate and its derivatives. Complex 2 exhibits a 3D (4,5)-connected framework with (4²·6⁷·8)(6⁴·8²)(4²·6⁴) topology. Complex 3 shows a 2D 3-connected network with 6³ topology. Complex 4 is a 2D (3,4,5)-connected framework with (4³)(3·4·5)(3·4²·8³)(3·4·5·6·7²·8²·9·10)(4³·5²·6²·7²·8) topology, whereas the structure of 5 has a 2D (3,4)-connected (4²·6)(4²·6³·8) framework. The 2D layers in 3 are extended to form a 2-fold interpenetrated 3D supramolecular network, and those in 4 and 5 afford the 3D supramolecular structures via H-bonding interactions. A structural comparison of these complexes demonstrates that the characteristics of auxiliary ligands play a key role in governing the coordination motifs and the final supramolecular lattices. Moreover, the magnetic properties of these Mn(II) complexes were investigated and discussed in detail.