Magnetic properties of a new N-TEMPO-tert-butyl substituted salicylaldimines and their biradical palladium(II) complexes

A new TEMPO bearing tert-butylated salicylaldimines 1 and 2, as well as early reported 3, and their bis(N-TEMPO-tert-butylated salicylaldiminato)palladium(II) biradical complexes 4–6 have been synthesized and characterized by elemental analyses, IR, UV/vis, ESR and an SQUID magnetometer. The solid state g-factors (2.0116–2.0168) for 4–6 suggest the existence of the significant metal-orbital contribution to the SOMO of nitroxyl radicals. The χmT vs. T plots for 1 and 2 indicate that the χmT decreases as T is lowered from 300 to 20 K, suggesting the existence of weak antiferromagnetic interactions in these radicals. Variable-temperature dependence (10–300 K) magnetic susceptibility data for biradical complexes 4–6 revealed the existence of ferromagnetic and antiferromagnetic behavior around at 10–220 K range for 4. The 1/χm data for 1–6 follow the Curie–Weiss law with negative θ throughout the above temperature range.

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► A series of new N-TEMPO-tert-butylated salicylaldimines and their Pd(II) complexes have been synthesized.
► Temperature dependence of magnetic behaviors of free radicals is unusual.
► Low-temperature magnetic measurements showed a weak ferromagnetic behavior in biradical complexes.
► Magnetic behaviors of all radicals well fitted by the Curie–Weiss law with a negative θ.