R-Isophthalate (R = –H, –NO2, and –COOH) as modular building blocks for mixed-ligand coordination polymers incorporated with a versatile connector 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole

Abstract

A series of nine Co^II, Cu^II, and Cd^II mixed-ligand coordination complexes with a 3,3′-dipyridyl connector 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole (3-bpt) have been achieved, by changing the incorporated benzenedicarboxylic co-ligands from isophthalic acid (H₂ip) to its 5-substituted derivatives 5-nitroisophthalic acid (–NO₂, H₂nip) and trimesic acid (–COOH, H₃tma). All compounds have been structurally determined by the X-ray diffraction technique. It is indicated that most of them are coordination polymers, with the ligands of benzenecarboxylic acids being doubly deprotonated to compensate the charge and bridge the metal ions, except for a monomeric ion-pair product [Co(3-bpt)₂(H₂O)₄]·(H₂tma)₂·(H₂O)₂ (1c). These polymers display a variety of coordination frameworks, such as 1-D double-strand chain, 2-D layer with (4,4) topology, 2-D double layer, 2-D layer with (6,3) topology and 1-D molecular ladder etc. The results evidently reveal the profound substituent effect of the R-isophthalate building blocks on engineering such coordination arrays, in virtue of the versatility of 3-bpt with diversiform configurations and binding fashions. Nevertheless, the choice of metal ion is also significant in the structural assembly, and the low-dimensional coordination networks are further extended to diverse 3-D supramolecular crystalline lattices via noncovalent interactions especially hydrogen bonding. Solid-state properties such as thermal stability and fluorescence have also been investigated.