Polycarboxylate-directed various Co(ii) complexes based on a “V”-like bis-pyridyl-bis-amide derivative: construction, electrochemical and photocatalytic properties

Abstract

A series of new Co(II) complexes based on a new semi-rigid “V”-like bis-pyridyl-bis-amide derivative, namely, [Co(3-bpha)₂(2,3-HPDC)₂] (1), [Co(3-bpha)(3-NPH)(H₂O)₂]·2H₂O (2), [Co(3-bpha)(1,3-BDC)]·4H₂O (3), [Co(3-bpha)(HIP)]·3H₂O (4), [Co(3-bpha)(MIP)(H₂O)]·H₂O (5), and [Co₃(3-bpha)₂(1,3,5-BTC)₂(H₂O)₄]·2H₂O (6) (3-bpha = N,N′-bis(pyridin-3-yl)-5-hydroxybenzene-1,3-dicarboxamide, 2,3-H₂PDC = 2,3-pyridinedicarboxylic acid, 3-H₂NPH = 3-nitrophthalic acid, 1,3-H₂BDC = 1,3-benzenedicarboxylic acid, H₂HIP = 5-hydroxyisophthalic acid, H₂MIP = 5-methylisophthalic acid, 1,3,5-H₃BTC = 1,3,5-benzenetricarboxylic acid), have been hydrothermally synthesized by tuning aromatic polycarboxylate co-ligands and characterized by single-crystal X-ray diffraction, IR spectra, powder XRD and TG analysis. Complex 1 is a discrete zero-dimensional (0D) structure in which the 3-bpha ligands and the 2,3-HPDC anions act as the terminal groups simultaneously to coordinate with the Co^II ions. Complex 2 is a 1D meso-helical chain in which the 3-bpha ligands show a μ₂-bridging mode and the 3-NPH anions act as the terminal groups. In complexes 3 and 4, pairs of 3-bpha ligands integrate with two Co^II ions to generate 28-membered Co₂(3-bpha)₂ rings, which connect with the 1D [Co-1,3-BDC]_n or [Co-HIP]_n chains to create the 2D networks. In complex 5, the Co^II ions are linked to 3-bpha ligands, resulting in a single-strand [Co-3-bpha]_n helix chain, which is further connected to the MIP anions to form a 2D network. Complex 6 shows a 3D framework with (3,3,4)-connected (8³)₄(8⁴·10²) topology, which contains [Co-(1,3,5-BTC)]_n 2D grid-like sheets and 1D [Co-3-bpha]_n helical chains. Finally, the 0D discrete architecture in 1, 1D chain in 2, and 2D networks in 4 and 5 are extended to 3D supramolecular frameworks through hydrogen-bonding interactions. The effect of polycarboxylate auxiliary ligands with different substitute groups and different carboxyl positions and number on the assembly and structures of the target complexes were discussed. Moreover, the thermal stabilities, electrochemical properties and photocatalytic activities of complexes 1–6 were investigated.