Ladder-Type Cu(II) Coordination Polymer with π–π Stacking of Planar Blatter Radical Ligands: Structural and Magnetic Characterization

The synthesis of two C(2)-pyridyl derivatives of the planar Blatter radical was developed by using the tris(trimethylsilyl)silane (TTMSS)-assisted cyclization of appropriate iodoarenes. These monodentate paramagnetic ligands were characterized by spectroscopic (UV–vis and electron paramagnetic resonance (EPR)) and electrochemical methods and reacted with (pdc)Cu(H₂O)₃. A complex containing the 3-pyridyl group was characterized structurally, revealing novel polymeric Cu–O–Cu–O ladders separated with slipped stacks of radical ligands. Superconducting quantum interference device (SQUID) magnetometry of this complex demonstrated strong antiferromagnetic interactions between the radicals and largely isolated Cu(II) ions. Analysis of the magnetic data with the Hatfield model, assuming two isolated one-dimensional (1D) alternating Heisenberg chains, gave J_RR/k_B = −1200 K and α_RR = 0.4 for the paramagnetic ligand stacks, and J_CuCu/k_B = −3.5 K and α_CuCu = 0.9 for the Cu(II) ion chains. Analysis of the experimental data was augmented with density functional theory (DFT) calculations.

(pdc)Cu(II) complex with a planar Blatter radical forms a novel ladder-type linear chain with adjacent slipped stacks of radicals exhibiting separate magnetic interactions.