A series of new mixed-ligand complexes based on 3,6-bis(imidazol-1-yl)pyridazine: syntheses, structures, and catalytic activities

Abstract

Seven new mixed-ligand complexes based on L [L = 3,6-bis(imidazol-1-yl)pyridazine], namely, [Ni(L)₂(SCN)₂]_n (1), [Cu₅(L)(1,2-BDC)₄(μ₃-OH)₂]_n (2), {[Cu₄(L)₂(1,3-HBDC)(1,3-BDC)(μ₃-OH)₄]·ClO₄·2.6H₂O}_n (3), {[Ni(L)(1,4-BDC)H₂O]·0.25H₂O}_n (4), [Co(L)(1,3,5-H₂BTC)₂H₂O]_n (5), {[Cu₂(L)(2,6-PYDC)₂(H₂O)₂]·4.4H₂O}_n (6), and {[Co(L)(4,4′-OBA)]·3.725H₂O}_n (7) [1,2-benzenedicarboxylic acid (1,2-H₂BDC), 1,3-benzenedicarboxylic acid (1,3-H₂BDC), 1,4-benzenedicarboxylic acid (1,4-H₂BDC), 1,3,5-benzenetricarboxylic acid (1,3,5-H₃BTC), 2,6-pyridine dicarboxylic acid (2,6-H₂PYDC), and 4,4′-oxydibenzoic acid (4,4′-H₂OBA)], have been synthesized by solvothermal reactions. Complexes 1 and 2 possess a two-dimensional (2D) layered structure, and the 2D framework of complex 1 can be rationalized to be a four-connected {4⁴·6²} topological sql network, while 2 exhibits a similar topological network with pentanuclear [Cu₅(μ₃-OH)₂(μ₂-COO⁻)₆]²⁺ secondary building units (SBUs). Complex 3 presents an 8-connected sqc3 3D framework based on a chair-shaped [Cu₄(μ₃-OH)₄]⁴⁺ SBU with a Schläfli symbol of {4²⁴·6⁴}. Complex 4 displays a 3D framework with diamondoid topology, which includes L/Ni(II)/L helical chains. Complex 5 features a 1D chain structure formed by L ligands. Complex 6 shows a dinuclear structure, which is arranged into a 1D supramolecular chain by hydrogen-bonding interactions. The 3D framework of 7 presents a 4-connected porous architecture with a Schläfli symbol of {6⁶}, the same as that of complex 4. The powder X-ray diffraction spectra, IR spectra, UV-vis absorption spectra and thermal stabilities of 1–7 have been investigated. Moreover, in the complex-catalyzed homocoupling reaction of 4-substituted aryl iodides, the catalytic activities of 1–7 have also been studied and discussed.