Strong Exchange Couplings Drastically Slow Down Magnetization Relaxation in an Air‐Stable Cobalt(II)‐Radical Single‐Molecule Magnet (SMM)

Abstract

The energy barrier leading to magnetic bistability in molecular clusters is determined by the magnetic anisotropy of the cluster constituents. By incorporating a highly anisotropic four‐coordinate cobalt(II) building block into a strongly coupled fully air‐ and moisture‐stable three‐spin system, it proved possible to suppress under‐barrier Raman processes leading to 350‐fold increase of magnetization relaxation time and pronounced hysteresis. Relaxation times of up to 9 hours at low temperatures were found.

Semiquinone radical-bridged M2 (M = Fe, Co, Ni) complexes with strong magnetic exchange giving rise to slow magnetic relaxation

“…In fact, the coupling constant for 4 is comparable to that determined for the o-semiquinone radical in the mononuclear [PhTt tBu ]Fe(phenSQ) complex (J Fe-L ¼ À127 cm À1 ). 31 Nevertheless, stronger exchange has been observed for semiquinonoid ligands with N-donors (J < À900 cm À1 with Fe 2+ and À440 cm À1 with Co 2+ ), 17,19 as expected for a more diffuse, higher-energy SOMO of N compared to O. 16,32 As such, incorporation of bridging ligands based on p-phenylenediamine radical may provide a route to complexes with even stronger coupling.…”

“…For instance, 2,5-disubstituted semiquinone derivatives, which can act as bis(bidentate) bridging ligands (Scheme 1, bottom), 11,12 have been employed to synthesize radical-bridged dinuclear complexes exhibiting strong magnetic exchange coupling [13][14][15][16] and in some cases single-molecule magnet behavior. [17][18][19][20] In contrast, magnetic coupling involving the bis(monodentate) benzosemiquinone molecule (Scheme 1, top) has not been reported.…”

Single-ion anisotropy and exchange coupling in cobalt(ii)-radical complexes: insights from magnetic and ab initio studies

“…11 Alternatively, metal-radical systems with an odd total number of unpaired electrons could be targeted, to retain Kramers' degeneracy, as has been achieved for symmetric radical-bridged Co(II) and lanthanoid(III) systems previously. 2,[4][5][6][7][8][9]11,12,69…”

“…36,53,67,68 Recently, Sarkar and van Slageren et al reported multicongurational calculations on a radical bridged dinuclear tetrahedral Co(II) complex, for which SOC acts at the second order. 69 Most oen multi-congurational techniques are used to dene the metal electronic state only in the absence of the radical. 2,34,63,64,[70][71][72][73][74] A multi-technique experimental approach combined with a multicongurational ab initio study is thus required to clarify the nature and the magnitude of the interactions in anisotropic metal-radical coupled systems and the way they can be varied to design improved bistable materials.…”

Drastische Verlangsamung der magnetischen Relaxation durch starke Austauschkopplungen in einem luftstabilen, radikalverbrückten Cobalt(II)‐Einzelmolekülmagneten

“…15) cm À1 , g Co,k = 2.85(3), und Abbildung 1. Die H-Atome (mit Ausnahme der NH-Gruppen)w urden zur Übersichtlichkeit nicht dargestellt [31]. Unten: ORTEP-Darstellung der Verbindung 2 als Ausschnitt der polymeren Kette im Einkristall.…”