Assembly and properties of transition-metal coordination polymers based on semi-rigid bis-pyridyl-bis-amide ligand: effect of polycarboxylates on the dimensionality

Abstract

Seven new coordination polymers, [Co(3-bpcd)(1,3-BDC)(H₂O)₃]·H₂O (1), [Co(3-bpcd)(1,2-BDC)(H₂O)]·H₂O (2), [Co₃(3-bpcd)(1,2,4-BTC)₂(H₂O)₄]·4H₂O (3), [Co(3-bpcd)(NPH)]·2H₂O (4), [Cu(3-bpcd)(1,3-BDC)] (5), [Cu(3-bpcd)(1,2-BDC)] (6), [Cu(3-bpcd)(1,3,5-HBTC)(H₂O)]₂·2H₂O (7) (3-bpcd = N,N′-bis(pyridin-3-yl)cyclohexane-1,4-dicarboxamide, 1,3-H₂BDC = 1,3-benzenedicarboxylic acid, 1,2-H₂BDC = 1,2-benzenedicarboxylic acid, 1,2,4-H₃BTC = 1,2,4-benzenetricarboxylic acid, H₂NPH = 3-nitrophthalic acid and 1,3,5-H₃BTC = 1,3,5-benzenetricarboxylic acid) have been hydrothermally synthesized by assembling transition-metal cobalt–copper salts with semi-rigid bis-pyridyl-bis-amide ligand 3-bpcd and different aromatic polycarboxylic acids. Complex 1 exhibits a one-dimensional (1D) sinusoidal-like chain, which is further assembled into a three-dimensional (3D) supramolecular framework through hydrogen-bonding interactions. Complex 2 possesses a 3D framework with 4-connected 6⁶ topology, which contains a two-dimensional (2D) distorted asymmetric hexagonal grid. When 1,2,4-BTC is used in complex 3, a 3D framework with (6³·8²·10)₂(6⁵·8)₂(8) topology is constructed. Complex 4 possesses a 3D framework with 4-connected 6⁶ topology, which is similar to that of 2 except for containing a 2D symmetric hexagonal grid. When Co^II ion is replaced by Cu^II ion, the 3D framework of complex 5 with (4·6²)(4·6⁶·8³) topology based on 3-bpcd and 1,3-BDC ligands is obtained. Complex 6 shows a 2D cross network consisting of a superposed Cu-3-bpcd 1D chain and 1,2-BDC, which is further expanded into a 3D supramolecular framework by hydrogen-bonding interactions. In complex 7, 1,3,5-HBTC is employed as the auxiliary ligand, and a 3D supramolecular framework based on the undulated 2D layers is formed through π–π stacking and hydrogen-bonding interactions. Both the metal ions and polycarboxylates play important roles in the construction of the title complexes. In addition, the electrochemical behaviors and the fluorescence properties of the seven complexes have been investigated.