Assembling metals (CoIIand MnII) with pyridylcarboxylates in the presence of azide: synthesis, structural aspects and magnetic behavior of three coordination polymers

Abstract

The reaction between Co(NO3)2·6H2O and substituted pyridylcarboxylic acid [nicotinic acid (Hnic) or trans-3-pyridylacrylic acid (Htpa)] in the presence of NaN3 under hydrothermal conditions yielded [Co1.5(nic)2 (Hnic)(N3)]n (1) and [Co1.5(tpa)2 (N3)(H2O)]n (2), respectively. Single crystal structure analyses reveal that both complexes are 3D complicated coordination polymers. The basic repeating units in both of the complexes are Co3 trinuclear clusters containing syn–syn bridging carboxylate and end-on azido linker. A similar reaction using MnCl2·4H2O in presence of equimolar amounts of Htpa and NaN3 yielded a 2D corrugated sheet [Mn(tpa)2]n (3) containing no azide. Complex 3 can also be synthesized under hydrothermal conditions using Natpa in the absence of NaN3. Surprisingly, the same reaction at room temperature yielded a known mononuclear complex [Mn(tpa)2(H2O)4]. Variable temperature magnetic studies down to 2 K revealed the dominant antiferromagnetic nature of the first two complexes with a ferrimagnetic type of behavior despite the facts that they are homometallic and homospin systems. The susceptibility data in both cases were analyzed by a Co3 trinuclear model as well as considering inter-trimer interactions. Complex 3 is weakly antiferromagnetic in nature with an exchange parameter of J = −2 cm−1 through the syn–anti bridging carboxylate pathway.