From Achiral Precursors to Copper Helical Coordination Polymers: Magnetic Properties and Electronic Structure

We introduce two novel one-dimensional coordination polymers (CPs) with helical arrangements based on copper(II) and an achiral Schiff base ligand, [Cu(L)(DMF)(X)]_n (X = NO₃^- (1) and Cl^- (2)), where L = 2-{[(pyridin-3-yl)imino]methyl}phenol. Both structures crystallize in an orthorhombic unit cell with a P2₁2₁2₁ space group. In both compounds, unconventional noncovalent interactions are fundamental for the structural features, modulating the dihedral angle ca. 70° between the two aromatic rings that are part of the organic ligand. Magnetic measurements indicate that weak antiferromagnetic interactions predominate in both CPs, with a J value of −3.34 cm^-1 for 1 and −4.95 cm^-1 for 2, corroborated by ab initio first-principles calculations. Furthermore, electronic structure analyses reveal a semiconductor behavior for both CPs. First-principles calculations predict small polaron localization around the Cu sites, with a higher formation of electron polarons in compound 1 than in 2.