Synthesis and magneto-structural analysis of H-bonded Cu/Ni-orotato coordination polymers

Abstract

Orotato based coordination network of formula [Cu(HOr)2]2−. 2(CH3)2―NH2+]n(1), and [Ni(HOr).3H2O]n (2), have been synthesized hydrothermally by self-assembly of orotic acid (H3Or) with metal salts Cu(OAc)2.H2O and Ni(NO3)2•6H2O respectively. Single crystal X-ray study confirms that in 1 electroneutrality is obtained with a compensating cation i.e. (CH3)2‒NH2+ and trans-trans μ2η1:η1 bridging carboxylate extend the Cu-Orotate moiety into 2D coordination network showing square lattice topology (sql) which through {…H‒N‒C = O} dimer yields into 3D hydrogen bonded coordination polymer.Temperature dependent measurements of magnetic susceptibility reveals the occurrence of competitive exchange interactions with weak ferromagnetic character in 1 (J = +0.31 cm–1) and weak antiferromagnetic interaction in 2 (J = - 0.52 cm–1). The dominantzero – field splitting effect is observed in Ni(II) ion. Two important magneticsuper exchange pathway transmitted through carboxylate oxygen of ligand through N‒H…O, and O‒H…O supramolecular synthons along with long Cu•••Cu separation of 6.635 Å (1) or Ni•••Ni separation of 7.700 Å (2). The DFT calculation analysis is used to rationalized the magnetic behavior in these coordination polymers.