From Achiral Precursors\nto Copper Helical Coordination\nPolymers: Magnetic Properties and Electronic Structure

We introduce two novel one-dimensional coordination polymers\n(CPs)\nwith helical arrangements based on copper(II) and an achiral Schiff\nbase ligand, [Cu(L)(DMF)(X)]<i><sub>n</sub></i> (X = NO<sub>3</sub><sup>–</sup> (<b>1</b>) and Cl<sup>–</sup> (<b>2</b>)), where L = 2-{[(pyridin-3-yl)imino]methyl}phenol.\nBoth structures crystallize in an orthorhombic unit cell with a <i>P</i>2<sub>1</sub>2<sub>1</sub>2<sub>1</sub> space group. In\nboth compounds, unconventional noncovalent interactions are fundamental\nfor the structural features, modulating the dihedral angle ca. 70°\nbetween the two aromatic rings that are part of the organic ligand.\nMagnetic measurements indicate that weak antiferromagnetic interactions\npredominate in both CPs, with a <i>J</i> value of −3.34\ncm<sup>–1</sup> for <b>1</b> and −4.95 cm<sup>–1</sup> for <b>2</b>, corroborated by ab initio first-principles\ncalculations. Furthermore, electronic structure analyses reveal a\nsemiconductor behavior for both CPs. First-principles calculations\npredict small polaron localization around the Cu sites, with a higher\nformation of electron polarons in compound <b>1</b> than in <b>2</b>.