| Summary: | A new asymmetrically substituted ONOO Schiff base ligand N-(2′-hydroxy-1′-naphthylidene)-3-amino-2-naphthoic acid (<b>nanc</b>H<sub>2</sub>) was prepared from the condensation of 2–hydroxy–1–naphthaldehyde and 3–amino–2–naphthoic acid. <b>nanc</b>H<sub>2</sub> reacts with Cu<sub>2</sub>(O<sub>2</sub>CMe)<sub>4</sub>·2H<sub>2</sub>O in the presence of Gd(O<sub>2</sub>CMe)<sub>3</sub>·6H<sub>2</sub>O to afford a uniform one-dimensional homometallic chain, [Cu<sup>II</sup>(<b>nanc</b>)]<i><sub>n</sub></i> (<b>1</b>). The structure of <b>1</b> 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 <b>nanc</b><sup>2−</sup> ligand and an O<sup>−</sup> of a bridging carboxylate group from a second ligand. The bridging carboxylato group of the <b>nanc</b><sup>2−</sup> ligand adopts a syn, anti-η<sup>1</sup>:η<sup>1</sup>:μ conformation linking neighboring Cu(II) ions, forming a 1D chain. The magnetic susceptibility of <b>1</b> follows Curie–Weiss law in the range 45–300 K (C = 0.474(1) emu K mol-1, <i>θ</i> = +7.9(3) K), consistent with ferromagnetic interactions between <i>S</i> = ½ 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 <i>J</i> = +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 (<i>J</i> = +13.8 K) is consistent with the observed ferromagnetic exchange between neighbouring Cu(II) centres.
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