Three copper(II) complexes connected through tetradentate carboxylate linkers and bidentate N-heterocyclic ligands: From 3-D MOF to 1-D chain

Three copper coordination polymers [Cu2(bbtc)(bbi)2]·3H2O (1) [bbi = 1,1-(1,4-butanediyl)bis(imidazole), bbtc = 3,3′,4,4′-benzophenonetetracarboxylate], [Cu3(Hbbtc)2(3-bpfp)3(H2O)2]·10H2O (2) [3-bpfp = bis(3-pyridylformyl)piperazine], and [Cu(H2bbtc)(4-bpfp)(H2O)]·H2O (3) [4-bpfp = bis(4-pyridylformyl)piperazine] have been hydrothermally synthesized by self-assembly of aromatic tetracarboxylate ligand bbtcd [bbtcd = 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride], and bidentate N-heterocyclic ligands bbi, 3-bpfp or 4-bpfp. X-ray diffraction analysis reveals that compound 1 is a novel three-dimensional (3-D) metal-organic framework with a binodal (4,4)-connected {62.84}{64.82}2 topology. Compound 2 possesses a two-dimensional (2-D) layered structure, in which a trinodal (3,4,4)-connected network with novel {3.62}2{3.63.72}2{32.62.72} topology can be found. Compound 3 displays a one-dimensional (1-D) ribbon polymer chain based on 4-bpfp ligands and H2bbtc2- anions. The adjacent layers for 2 and the adjacent chains for 3 are further linked by hydrogen bonding and π–π stacking interactions to form 3-D supramolecular networks. Importantly, bbtcd with different protonation extent displays three different coordination modes in compounds 1–3: the four carboxyl groups of bbtc4- anions combine with CuII ions by tetra(monodentate) mode in 1, three carboxyl groups of Hbbtc3− anions show tri(monodentate) coordination mode and the fourth carboxyl group is protonated in 2, whereas for 3 only two carboxyl groups H2bbtc2− anions adopt bis(monodentate) coordination mode and the other two are protonated. N-heterocyclic ligands play important roles in the construction of title complexes with different dimensionality. In addition, the electrochemical properties of the three copper compounds bulk-modified carbon paste electrodes have been reported.

Three copper coordination polymers have been obtained from hydrothermal reactions. They respectively exhibit 3-D framework, 2-D layer and 1-D ribbon chain for 1–3. In three complexes, the bbtc displays tetra(monodentate), tri(monodentate) and bis(monodentate) coordination modes. The electrochemical properties of the complexes modified carbon paste electrodes have been reported.Figure optionsDownload as PowerPoint slideHighlights
► N-donor ligands bbi, 3-bpfp and 4-bpfp are introduced into the {M-bbtc} system.
► Three new coordination polymers from 3-D MOF to 1-D chain are formed.
► Bbtcd with different protonation extent shows different coordination modes in 1–3.
► 1-, 2- and 3-CPEs show good electrochemical properties.