Field-induced single ion magnet behaviour of discrete and one-dimensional complexes containing [bis(1-methylimidazol-2-yl)ketone]-cobalt() building units

We describe herein the first examples of six-coordinate Co II single-ion magnets (SIMs) based on the β-diimine Me bik ligand [ Me bik = bis(1-methylimidazol-2-yl)ketone]: two mononuclear [Co II ( R bik) 2 L 2 ] complexes and one mixed-valence {Co III 2 Co II } n chain of formulas [Co II ( Me bik)(H 2 O)(dmso)(μ-NC) 2 Co III 2 (μ-2,5-dpp)(CN) 6 ] n ·1.4 n H 2 O ( 3 ) [L = NCS ( 1 ), NCSe ( 2 ) and 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine ( 3 )]. Two bidentate Me bik molecules plus two monodentate N -coordinated pseudohalide groups in cis positions build somewhat distorted octahedral surroundings around the high-spin cobalt( ii ) ions in 1 and 2 . The diamagnetic [Co III 2 (μ-2,5-dpp)(CN) 8 ] 2− metalloligand coordinates the paramagnetic [Co II ( Me bik)(H 2 O)(dmso)] 2+ complex cations in a bis-monodentate fashion to afford neutral zigzag heterobimetallic chains in 3 . Ab initio calculations, and cryomagnetic dc (2.0-300 K) and ac (2.0-12 K) measurements as well as EPR spectroscopy for 1-3 show the existence of magnetically isolated high-spin cobalt( ii ) ions with D values of 59.84-89.90 ( 1 ), 66.32-93.90 ( 2 ) and 70.40-127.20 cm −1 ( 3 ) and field-induced slow relaxation of the magnetization, being thus new examples of SIMs with transversal magnetic anisotropy. The analysis of their relaxation dynamics reveals that the relaxation of the magnetization occurs by the Raman (with values of the n parameter covering the range 6.0-6.8) and direct spin-phonon processes. Three {Co II ( R bik) 2 } single-ion magnets (SIMs) based on the Me bik ligand [ Me bik = bis(1-methylimidazol-2-yl)ketone] and one mixed-valence {Co III 2 Co II } n chain of Co II SIMs connected by diamagnetic {Co III 2 (μ-2,5-dpp)(CN) 8 } spacers are discussed.