Synthesis, crystal structures and magneto-structural correlations study of three 3d metal–radical heterospin complexes

Three heterospin complexes [M(NIT4Py)2(cda)H2O] (M = Cu(II) (1), Ni(II) (2), Co(II) (3)) with various paramagnetic 3d metal ions and pyridyl-substituted nitronyl nitroxide radical (NIT4Py = 2-(4′-pyridyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, H2cda = 4-hydroxy-pyridine-2,6-dicarboxylic acid) have been synthesized, characterized structurally and magnetically. The single crystal structures show that complexes 1–3 are isomorphic, and have 2D supramolecular network consisting of [M(NIT4Py)2(cda)H2O] with three paramagnetic centers. The magnetic measurements indicated that complexes 1–3 exhibit all antiferromagnetic interactions between M(II) and radicals with JCu–rad = −7.30 cm−1, JNi–rad = −3.58 cm−1 and JCo–rad = −1.85 cm−1, respectively. Their magnetic behaviors were interpreted in terms of the spin polarization mechanism of the π-electrons of NIT4Py and the orthogonality of 3d magnetic orbital of M(II) ion and the 2pπ orbital on the pyridine rings of NIT4Py.

Graphical abstractThree heterospin complexes with paramagnetic 3d metal ions (Cu(II), Co(II), Ni(II)) and pyridyl-substituted nitronyl nitroxide radical have been synthesized and structurally characterized. The magnetic behaviors of the three complexes exhibit all antiferromagnetic M(II)–radical interactions. And the magnetic properties were studied based on the orthogonality of orbitals and spin polarization mechanism of radical.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Three 3d metal–radical heterospin complexes were successfully synthesized. ► Complexes 1–3 are described as 2D supramolecular network with 3d paramagnetic centers. ► The magnetic measurements indicated that complexes 1–3 exhibit all antiferromagnetic interactions between 3d metal and radicals.