Slow Magnetic Relaxation Triggered by a Structural Phase Transition in Long-Chain-Alkylated Cobalt(II) Single-Ion Magnets

Abstract

The behavior of single-ion magnets (SIMs) that reflects large distortions of their coordination environments caused by the packing of long alkyl chains for two Co­(II) complexes of the type [Co­(C n -terpy)2]­(BF4)2 (C n -terpy = 4′-alkoxy-2,2’:6′,2″-terpyridine; n = 10 (1), 16 (2)) is reported. 1·2MeOH, which features a highly distorted octahedral high-spin Co­(II) center, exhibits field-induced slow magnetic relaxation under an applied dc field of 1000 Oe. Further detailed analysis of the relaxation process indicated the prevalence of the Raman process at low temperature. Surprisingly, 2 shows a reverse spin transition (rST) and also exhibits remarkable field-induced SIM behavior, revealing the presence of magnetic anisotropy for this high-spin Co­(II) species that is triggered by a structural phase transition. We present here the first examples of the coexistence of field-induced slow magnetic relaxation and rST associated with structural phase transitions involving long-alkyl-chain conformational changes from gauche to anti. These results indicate the prospect of inducing SIM properties in other distorted high-spin Co­(II) species bearing long alkyl chains.

Origin of the anomalously low Raman exponents in single molecule magnets

“…28,29 Nevertheless, exponents this big has been rarely observed in SMMs, and a large bulk of observations gives n = 3 ∼ 5 (see e.g. 5,11,16,[22][23][24][25][26][27] ). These unconventional values are usually left unexplained or ascribed to the optical-acoustic mechanism.…”

“…One of the outstanding issues is the presence of anomalous Raman exponents (see e.g. 5,11,16,[22][23][24][25][26][27] ) that generally deviates from the standard values. 28,29 Considering that the magnetic hysteresis usually occurs jointly with the dominance of Raman relaxation, 15,16 the Raman regime appears to be suitable for computing and sensing applications and deserves careful investigations.…”

Insertion of single-ion magnets based on mononuclear Co(ii) complexes into ferromagnetic oxalate-based networks

“…S13 in the ESI†). 21 c ,22 e , f ,30–32 This reduction in the value of n can be due to different mixtures in the eigenvector of the Kramers doublets and the consideration of other phonons. 33…”

The Structural and Magnetic Properties of FeII and CoII Complexes with 2-(furan-2-yl)-5-pyridin-2-yl-1,3,4-oxadiazole

“…The modification of U eff is accomplished by increasing magnitude of the zero-field splitting parameter D, due to a simple relationship among them, U = |D|(S 2 − 1/4) for half-integer spin and U = |D|(S 2 ) for integer spin, and it holds that values of ZFS (zero-field splitting) parameters are dictated by the coordination number, the ligand field, and the symmetry of the coordination polyhedron. In general, higher |D|-values should yield higher U eff and correspondingly higher T B [8][9][10][11]. However, large zero-field splitting parameter E causes an increase of the tunneling rate of the magnetization.…”