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.