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

The reaction between Co(NO3)(2)center dot 6H(2)O and substituted pyridylcarboxylic acid [nicotinic acid (Hnic)or trans-3-pyridylacrylic acid (Htpa)]in the presence of NaN3 under hydrothermal conditions yielded [Co-1.5(nic)(2) (Hnic)(N-3)](n) (1)and [Co-1.5(tpa)(2) (N-3)(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 Co-3 trinuclear clusters containing syn-syn bridging carboxylate and end-on azido linker. A similar reaction using MnCl2 center dot 4H(2)O 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 Co-3 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.