Synthesis, Structural, Magnetic and Computational Studies of a One-Dimensional Ferromagnetic Cu(II) Chain Assembled from a New Schiff Base Ligand

A new asymmetrically substituted ONOO Schiff base ligand N-(2 '-hydroxy-1 '-naphthylidene)-3-amino-2-naphthoic acid (nancH(2)) was prepared from the condensation of 2-hydroxy-1-naphthaldehyde and 3-amino-2-naphthoic acid. nancH(2) reacts with Cu-2(O2CMe)(4)center dot 2H(2)O in the presence of Gd(O2CMe)(3)center dot 6H(2)O to afford a uniform one-dimensional homometallic chain, [Cu-II(nanc)](n) (1). The structure of 1 was elucidated via single crystal X-ray diffraction studies, which revealed that the Cu(II) ions adopt distorted square planar geometries and are coordinated in a tridentate manner by an [ONO] donor set from one nanc(2-) ligand and an O- of a bridging carboxylate group from a second ligand. The bridging carboxylato group of the nanc(2-) ligand adopts a syn, anti-eta(1):eta(1):mu conformation linking neighboring Cu(II) ions, forming a 1D chain. The magnetic susceptibility of 1 follows Curie-Weiss law in the range 45-300 K (C = 0.474(1) emu K mol-1, theta = +7.9(3) K), consistent with ferromagnetic interactions between S = 1/2 Cu(II) ions with g = 2.248. Subsequently, the data fit well to the 1D quantum Heisenberg ferromagnetic (QHFM) chain model with g = 2.271, and J = +12.3 K. DFT calculations, implementing the broken symmetry approach, were also carried out on a model dimeric unit extracted from the polymeric chain structure. The calculated exchange coupling via the carboxylate bridge (J = +13.8 K) is consistent with the observed ferromagnetic exchange between neighbouring Cu(II) centres.