Magnetic Exchange Interaction in [BNITPhOPr] and [Cu(Cl2CHCO2)2(NITpPy)2(H2O)]: A Density Functional Theory Study

Abstract

AbstractThe magnetic exchange interaction and electronic structures for the nitronyl nitroxide free radical (1), (4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐oxyl 3‐oxide), nitronyl nitroxide biradical, [BNITPhOPr] (2), (1,3‐[di‐2‐(4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐oxyl 3‐oxide)phenoxy]propane) and CuII‐nitronyl nitroxide radical complex, [Cu(Cl2CHCO2)2(NITpPy)2(H2O)] (3), (NITpPy=2‐(4‐pyridyl)‐4,4,5,5‐tetramethyl‐2‐imidazoline‐1‐oxy 3‐oxide) were studied by the broken symmetry (BS) approach within the density functional theory (DFT), combined with the spin‐Hamiltonian full‐matrix diagonalization method. The theoretically calculated magnetic coupling constant J values (‐0.10 (2), −12.9 (3)) are approximately consistent with experimental results (‐0.24 (2) and‐11.5 (3)). For the complex 3, the magnetic coupling constant j (‐0.85) between two terminal radical ligands is also obtained, which has not been characterized experimentally. In contrast to radical 1, the nitronyl nitroxide radicals in the biradical 2 and complex 3 behave as a more localized spin‐center. However, CuII ion of the complex 3 exhibits a local‐spin delocalization to the surrounding atoms. Spin population analyses suggest that the intramolecular antiferromagnetic coupling for the biradical 2 is governed by the weak spin polarization through the bridging ligand and that the antiferromagnetic coupling interaction between the CuII ion and nitronyl nitroxide radicals in the complex 3 is dominated by both the local‐spin delocalization on the CuII ion and the global spin polarization mechanism.