Metal-directed assembly of coordination polymers with the versatile ligand 2-(1H-benzotriazol-1-yl) acetic acid: from discrete structures to two-dimensional networks

Abstract

Eight new metal coordination complexes, namely, [Co(BTA)₂(H₂O)₄]·6H₂O (1), [Ni(BTA)₂(H₂O)₄]·6H₂O (2), [Cu₂(HBTA)₄(BTA)₂]·2H₂O (3), [Ag(BTA)(H₂O)]_n (4), [Zn(BTA)₂(H₂O)]_n (5), [Cd(BTA)₂(H₂O)]_n (6), [Cu₂(μ₃-OH)(BTA)₃]_n (7), and [Mn(BTA)₂(H₂O)₂]_n (8) [HBTA = 2-(1H-benzotriazol-1-yl)acetic acid], were obtained under hydrothermal conditions, by reacting the different metal salts with HBTA. The ligand HBTA was characterized by melting point (m.p.), elemental analysis (EA), infrared spectroscopy (IR), ¹H NMR, and X-ray single-crystal diffraction. Complexes 1–8 were structurally characterized by X-ray single-crystal diffraction, EA, IR, PXRD, and thermogravimetry analysis (TGA). These complexes all display low-dimensional features displaying various zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) coordination motifs. Complexes 1 and 2 are isostructural and mononuclear; they show unique decamer water clusters with bis-boat conformations, which further extend to a 1D metal–water chain. Through intermolecular hydrogen bonds, these 1D metal–water chains extend to 3D supramolecular networks. Complex 3 shows a bi-nuclear structure. Complex 4 displays a 1D tape structure. There exist weak interactions between Ag⋯Ag. Complexes 5 and 6 form a 1D linear chain bridged by BTA anions. Complex 7 exhibits a 2D layer containing tetranuclear butterfly [Cu₄(CO₂)₄(μ₃-OH)] secondary building units (SBUs). Complex 8 possesses a 2D layer and further stacks via hydrogen bonding interactions to generate a three-dimensional supramolecular architecture. These results suggest that both the coordination preferences of the metal ions and the versatile nature of this flexible ligand play a critical role in the final structures. The luminescent spectra show strong emission intensities in complexes 3, 4, 5, and 6. Complexes 3, 5 and 6 display blue photoluminescence. However, complex 4 exhibits green fluorescence. Variable-temperature magnetic susceptibility measurements reveal the existence of antiferromagnetic interactions in both 7 and 8. Additionally, the ferroelectric and second-harmonic generation (SHG) properties of 5 are discussed in detail.