Mononuclear and One‐Dimensional Cobalt(II) Complexes with the 3,6‐Bis(picolylamino)‐1,2,4,5‐tetrazine Ligand

We describe herein the synthesis and structural characterization of a tetrazine‐based bis(picolylamine) ligand, namely, N3,N6‐bis(pyridin‐2‐ylmethyl)‐1,2,4,5‐tetrazine‐3,6‐diamine (L, 1), which was prepared by the direct reaction between 2 equiv. of picolylamine and 3,6‐dichloro‐1,2,4,5‐tetrazine. Its reaction with cobalt(II) hexafluoroacetylacetonate hydrate afforded the mononuclear complex [Co(hfac)2L]·CH3CN (2, Hhfac = hexafluoroacetylacetone) and the chain compound {[Co(hfac)2(µ‐L)][Co(hfac)2(CH3OH)2]}n (3). The crystal structures of 1–3 were determined by X‐ray structure analysis. The metal centre in 2 is trischelated by two hfac ligands and one picolylamine unit. The two crystallographically independent cobalt(II) ions in 3 (Co1 and Co2) are six‐coordinate. Two bidentate hfac groups in equatorial positions and two trans‐positioned pyridine nitrogen atoms build the coordination polyhedron around Co1 to form a neutral zigzag chain compound, which cocrystallizes with the mononuclear species trans‐[Co2(hfac)2(CH3OH)2]. The magnetic properties of 2 and 3 were investigated in the temperature range 1.9–300 K. The decrease of the χMT values of 2 and 3 upon cooling is mainly due to the depopulation of the higher energy Kramers doublets of the magnetically isolated six‐coordinate cobalt(II) ions. Alternating‐current (ac) magnetic susceptibility measurements of 2 and 3 revealed the occurrence of frequency‐dependent out‐of‐phase signals under applied direct‐current (dc) fields at very low temperatures, and this result is indicative of single‐ion magnet (SIM) behaviour. The 3,6‐bis(picolylamine)‐1,2,4,5‐tetrazine ligand provides mononuclear and one‐dimensional polymer chain cobalt(II) complexes that show magnetic properties indicative of single‐ion magnet (SIM) behavior.