Variations in the structural composition of pyrazole-3,5-dicarboxylato Cu(ii) complexes with 1,2-di(4-pyridyl)ethane synthesized under different conditions

Abstract

The reaction of Cu(II) and pyrazole-3,5-dicarboxylic acid (H₃pzdc) with 1,2-di(4-pyridyl)ethane (bpa) at various temperatures and solvents results in the formation of seven new Cu(II) complexes, namely, [Cu₂(pzdc)₂(H₂O)₂](H₂bpa)(H₂O)₆ (1), [Cu₂(pzdc)₂(H₂O)₂](H₂bpa)(H₂O)₄ (2), [Cu₃(pzdc)₂(H₂O)₄(bpa)]_n (3), [Cu₄(pzdc)₄(H₃pzdc)₂(H₂O)₂](H₂bpa)₂(H₂O)₂ (4), {[Cu₄(pzdc)₄(bpa)₂](DMF)(NH₂(CH₃)₂)₄}_n (5), {[Cu₂(pzdc)₂](H₂bpa)}_n (6), and {[Cu₂(pzdc)(bpa)₂](BF₄)}_n (7). Complexes 1 and 2 were prepared in an aqueous solution at different temperatures. Similar cyclic dinuclear Cu(II) anionic units are present in both complexes, but their crystal structures and lattice water molecule contents are different. When the aqueous medium was replaced with different solvent mixtures under the same hydrothermal conditions as 2, a variety of Cu(II) complexes 3–7 were generated. A one-dimensional (1D) coordination chain containing a [Cu₃(pzdc)₂] secondary building unit of 3 was obtained in a water and N,N′-dimethylformamide (DMF) mixture. An anionic tetranuclear Cu(II) complex of 4 was formed in water and an ethanolic mixture. When using pure DMF, an anionic 1D zigzag coordination chain of 5 was obtained. Whereas a 1D ladder-like coordination chain of 6 was formed in a DMF and acetonitrile (MeCN) mixture. Upon using EtOH or MeCN, a 3D pillar-layer cationic coordination framework of 7 was produced. Moreover, the temperature and solvent induced structural transformation of complex 1 was revealed.