Crystal architecture and magnetic properties of four transition-metal adipate coordination polymers

Abstract

The crystal structures have been determined and the magnetic properties investigated for four novel [M^II(A)(H₂O)_m]_n polymeric complexes, where M^II = Cd^II, Cu^II or Ni^II, m = 2–4 and A = adipate dianion. In [Cd(A)(H₂O)₂]_n1, [Cu(A)(H₂O)₂]_n2 and [Ni(A)(H₂O)₄]_n4 the combination of the metal cation with the dicarboxylate ligand leads to the formation of infinitive chains; still the co-ordinated water molecules and the carboxylate oxygen atoms collaborate to hydrogen-bond the chains into 3-D structures. Each cadmium(II) and nickel(II) ion in 1 and 4 is coordinated in an octahedral geometry to carboxylate and water molecules. The coordination sphere around copper(II) ions in 2 is square planar. The structure of 3, [Cu₃(A)₂(OH)₂(H₂O)₄]_n, is made up of ribbons linked to neighboring ones by hydrogen bonds. Each ribbon is composed of 2 crystallographically independent metal centers, Cu(1) and Cu(2), which exhibit octahedral and square pyramidal coordination geometries, respectively. Weak antiferromagnetic interactions were observed for 2, and 3 (singlet–triplet energy gap values of −2.3 and −54.5 cm⁻¹, respectively) and isolated nickel(II) ions for 4. An interpretation of the magnetic behavior was attempted. The strategy for the assembly of 1-D metal–organic chains into 3-D structures, with the use of coordinated water molecules as hydrogen bond donors and carboxylate oxygens as hydrogen bond acceptors, is also discussed.