Five new metal(II) complexes with 3-D network structures based on carboxylate and bis(imidazole) ligands: syntheses and structures

Abstract

The imidazolyl ligands, bis(N-imidazolyl)methane (L1) and 1,4-bis(N-imidazolyl)butane (L2) reacted with Zn(II), Cu(II), and Ni(II) salts of carboxylic acids resulting in the formation of five metal–organic coordination architectures, [Zn(L1)(CO₃)] · H₂O (1), [Cu(L2)(cnic)₂] · H₂O (2) (cnic = 2-chloronicotinate), [Cu₂(L2)₂(adip)₂] · 6H₂O (3) (adip = adipate), [Ni(mal)(L1)(H₂O)] (4) (mal = malonate), and [Ni₃(ctc^{3 −} )₂(L1)₆] · 35H₂O (5) (ctc ⁻  = citrate). All complexes have been characterized by elemental analysis, infrared, TG, and X-ray diffraction analyses. The different coordination modes of the carboxylates due to their chain length and rigidity lead to a range of different coordination structures. All these complexes display 3-D framework structures with a number of non-conventional weak interactions. The carboxylates can adopt bridging μ ₂, chelating μ ₂, chelating-bridging μ ₃, and chelating μ ₃ coordination modes. The metals are coordinated in N₂O₂, N₂O₃, N₂O₄, N₃O₃, and N₆ fashions depending on the metal and ancillary ligands. The frameworks of the five compounds are thermally stable.

Keywords:

• Carboxylic acid
• Zn(II)
• Cu(II)
• Ni(II)
• Mixed ligands
• Coordination polymers

Acknowledgments

We gratefully acknowledge the Education Office Foundation of Zhejiang Province (Project No. Y201017321) and the Zhejiang A & F University Science Foundation (Project No. 2009FK63) for the financial support.