Functionalization of Nitronyl-Nitroxide Ligands via Schiff Condensations: Rational Synthesis of Binuclear Complexes with Bis-Nitronyl-Nitroxide Ligands

Starting from 2,6-diformyl-p-cresol, only one formyl group has been transformed into the mono nitronyl-nitroxide radical, HL2 (2-(2-hydroxy-3-formyl-5-methylphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl 3-oxide). The presence of the formyl group in HL2 allows further functionalization using Schiff condensation reactions. HL2 has been reacted with 1,3-diaminopropane, benzylamine, and 2-picolylamine, generating a family of three new ligands, H2L4, HL5, and HL6, with H2L4 being a biradical. Using HL2 and H2L4 as ligands, five binuclear complexes, [Zn2(L2)2(hfac)2] (1) and [M2(L4H2)(hfac)4], where M = Mn (2), Co (3), Ni (4), and Zn (5), hfac– = hexafluoroacetylacetonate ligand, have been obtained. The crystal structures of complexes 1–5 have been solved. Compound 1 presents two polymorphs. The metal ions from compounds 2–5 adopt an octahedral geometry, being coordinated by phenoxido and aminoxyl oxygen atoms from the ligand and four oxygen atoms from the hfac– ligand. The cryomagnetic investigation of the three similar compounds, 2–4, reveals relatively strong antiferromagnetic MII-Rad interactions (JMnRad = −82 cm–1, JCoRad = −27.6 cm–1, and JNiRad = −185 cm–1, with H = −2JSMSRad).