Fluorescent recognition of Fe3+ and Fe3+-functionalized composite materials for enhancing photocatalytic activities of CoII complexes

Abstract

Six new Co^II coordination polymers (CPs) based on a bi-methylene-bridged semi-rigid bis-pyridyl-bis-amide ligand and various polycarboxylates, namely, [Co(4-bmbpd)(1,4-BDC)(H₂O)₂]·2H₂O (1), [Co(4-bmbpd)(OBA)]·H₂O (2), [Co(4-bmbpd)(2,2′-BDC)]·H₂O (3), [Co(4-bmbpd)(5-NIP)]·2H₂O (4), [Co(4-bmbpd)_0.5(5-AIP)]·H₂O (5), and [Co₃(4-bmbpd)₃(1,3,5-BTC)₂(H₂O)₄]·4H₂O (6) [4-bmbpd = N,N′-bis(4-methylenepyridin-4-yl)-1,4-benzenedicarboxamide, 1,4-H₂BDC = 1,4-benzenedicarboxylic acid, H₂OBA = 4,4′-oxybisbenzoic acid, 2,2′-H₂BDC = 2,2′-biphenyldicarboxylic acid, H₂NIP = 5-nitroisophthalic acid, 5-H₂AIP = 5-aminoisophthalic acid, and 1,3,5-H₃BTC = 1,3,5-benzenetricarboxylic acid] have been synthesized and structurally characterized by single-crystal X-ray diffraction analyses, IR spectroscopy, thermal gravimetric analyses (TG) and powder X-ray diffraction (PXRD). Complex 1 is a 2D 4-connected layer structure consisting of 1D [Co-(4-bmbpd)]_n wave-like chains and [Co-(1,4-BDC)]_n linear chains. 2 is also a 2D 4-connected network composed of 1D [Co-OBA]_n linear chains and [Co-(4-bmbpd)]_n wave chains. Complex 3 shows a (3,5)-connected 2D architecture based on 1D [Co-BDC]_n double linear chains and 1D [Co-(4-bmbpd)]_n zigzag chains with a {4²·6⁷·8}{4²·6} topology. In 4, two 4-bmbpd ligands coordinate with two Co^II ions in an anti-configuration to form a 38-membered [Co₂(4-bmbpd₂)] loop, which is further extended into a 1D tubular structure by pairs of 5-NIP anions. Coordination polymer 5 is a 3D (4,5)-connected architecture with a {4⁴·6²}{4⁴·6⁶} topology. 6 shows a 3D (2,3,4,4)-connected framework, which contains 1D [Co-1,3,5-BTC]_n double chains. The Co^II ion and 4-bmbpd ligand in the title coordination polymers show different coordination characters and conformations. The effect of organic polycarboxylates with different rigidities/lengths/substituents on the structures of Co^II coordination polymers was investigated. The electrochemical behaviors of 1–3, 5 and 6, the fluorescent behaviors of 5 and 6, and the photocatalytic activities of 5, 6, and Fe³⁺-functionalized Fe³⁺@5 and Fe³⁺@6 composites were investigated.