Two-Dimensional Nitronyl Nitroxide–Cu Networks Based on Multi-Dentate Nitronyl Nitroxides: Structures and Magnetic Properties

Abstract

Two multi-dentate nitronyl nitroxide radicals, namely, bisNITPhPy ([5-(4-pyridyl)-1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)]benzene) and NIT-3Py-5-4Py (2-{3-[5-(4-pyridyl)]pyridyl}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), were assembled with CuII ions to obtain two-dimensional heterospin 2p–3d coordination polymers [Cu7(hfac)14(bisNITPhPy)2]n (1) and [Cu2(hfac)4(NIT-3Py-5-4Py)]n (2) (hfac: hexafluoroacetylacetonate). In both compounds, the bisNITPhPy and NIT-3Py-5-3Py radicals acted as pentadentate and tetradentate ligands, respectively, to connect with CuII ions, generating a 2D layer structure. The analysis of the magnetic behavior indicated that strong antiferromagnetic coupling and ferromagnetic interaction (J = 17.1 cm−1) coexisted in 1. For 2, there were ferromagnetic couplings between the CuII ion and NO group, as well as the CuII ion and radical via the pyridine ring with J1 = 32.8 and J2 = 2.2 cm−1, respectively.

Cyclic [Cu-biRadical]2 Secondary Building Unit in 2p-3d and 2p-3d-4f Complexes: Crystal Structure and Magnetic Properties

“…The value obtained for J 1 confirms a strong and antiferromagnetic Cu-NO eq interaction, which can be attributed to the effective overlap of the magnetic orbital (d x 2 -y 2 ) of the Cu II ion and the magnetic π* orbital of the radical [ 1 ]. The obtained value (−350 cm −1 ) is comparable to those reported for the equatorial coordination of NIT to Cu II [ 55 , 56 , 57 , 58 ]. The positive value for J 2 confirms the anticipated ferromagnetic Cu-NO axial interactions resulting from the orthogonality of the magnetic orbitals (d x 2 -y 2 ) of Cu II and π* of the radical [ 59 ].…”