Structural diversity and photocatalytic activity of six Co(ii)/Ni(ii) complexes with three flexible phenylenediacetate isomers

Abstract

Six new Co(II)/Ni(II) coordination polymers, [Ni₃(opda)₃(mbib)₄(H₂O)₄]·2H₂O (1), [Ni(mpda)(mbib)]·H₂O (2), [Ni(ppda)(mbib)]·H₂O (3), [Co(opda)(pbib)(H₂O)] (4), [Co(mpda)(pbib)_1.5] (5), and [Co(ppda)(pbib)(H₂O)₂]·2H₂O (6) (H₂opda = 1,2-phenylenediacetic acid, H₂mpda = 1,3-phenylenediacetic acid, H₂ppda = 1,4-phenylenediacetic acid, mbib = 1,3-bis(1-imidazoly)benzene, and pbib = 1,4-bis(1-imidazoly)benzene), were synthesized using Co(II)/Ni(II) salts and the bis(imidazole) ligand in the presence of three different flexible phenylenediacetate isomers under hydrothermal conditions. In 1, the opda²⁻ ligand exhibits a trans-conformation and acts as a bridging building block extending a 1D loop-containing (Ni–mbib) polymer chain into a 2D network. In 2 and 3, mpda²⁻ and ppda²⁻ ligands possess a cis-conformation and can be seen as a “V”-type building block, linking Ni(II) atoms to form a 1D loop-containing chain together with the mbib ligand. Utilizing the isomer bridging ligand pbib and a different metal ion, Co(II), instead of the mbib ligand and Ni(II) ion, 2D (4), 1D (5), and 2D (6) coordination polymers were obtained. The structural diversity of these complexes is mainly attributed to the different coordination modes and isomer conformations of flexible phenylenediacetic acids and the bis(imidazole) ligand. Furthermore, six Co(II)/Ni(II) coordination polymers could accelerate the degradation rate of methylene blue (MB) under visible light irradiation, especially complex 4. Complex 2 exhibited a high performance in the oxygen evolution reaction (OER). Results will provide an effective way to develop coordination polymers towards electrochemical applications.