Probing the Axial Distortion Effect on the Magnetic Anisotropy of Octahedral Co(II) Complexes

Abstract

Three mononuclear octahedral Co(II) complexes are reported, [Co(py) 4 (SCN) 2 ] (1), [Co(py) 4 (Cl) 2 ]•H 2 O (2), and [Co(py) 4 (Br) 2 ] ( 3), that exhibit different distortions with compression (1) or elongation (2 and 3) of the axial positions. Easy plane magnetic anisotropy was confirmed by magnetic, HF-EPR, and computational studies for all complexes. Further analyses indicate that both the sign and magnitude of zero-field splitting parameters experience a significant change (D ≥ ±150 cm −1 ) by tuning of the axial and equatorial ligand field strength. Slow magnetic relaxation is observed for all compounds which is dominated by the Raman process involving both acoustic and optical phonons.

Modulating Magnetic and Photoluminescence Properties in 2‐Aminonicotinate‐Based Bifunctional Coordination Polymers by Merging 3d Metal Ions

“…Making use of Equation , which considers both processes, in which the first term corresponds to the one‐phonon process (dominant in the low‐temperature regime) and the second term stands for the two‐phonon Raman process (responsible for the increase of the relaxation time at high temperatures), the following set of parameters are obtained: A direct =1282 s −1 K −1 , B Raman =1.38 s −1 K − n , n= 5.7. Notably, these values are in line with those previously reported for SIMs based on Co II …”

Role of Coordination Number and Geometry in Controlling the Magnetic Anisotropy in FeII, CoII, and NiII Single‐Ion Magnets

“…For example, complexes cis ‐[Co II (dmphen) 2 (NCS) 2 ] [15] ( 8 ) (dmphen=2,9‐dimethyl‐1,10‐phenanthroline) and [Co(μ‐L)(μ‐CH 3 COO)Y(NO 3 ) 2 ] [25h] ( 9 ) (L=ferrocene based compartmental ligand) were found to possess very high easy‐plane anisotropy with D values of +98 cm −1 and +92 cm −1 with small U eff values of 17.0 cm −1 and 7.6 cm −1 , respectively (see Figure 3 b and Table 1). Very recently, Dunbar and co‐workers reported three pseudo‐octahedral complexes of general formula [Co(py) 4 X 2 ] [26] (where X=SCN, Cl and Br) out of which the Cl and the Br analogues (complexes 10 and 11 ) exhibit very high D values of +127 cm −1 and +139 cm −1 as obtained from NEVPT2 calculations along with U eff values of 19.3 cm −1 and 20.4 cm −1 , respectively, in the presence of a dc field (see Figure 3 c). Soon after, the same group reported another pseudo‐octahedral complex [Co(MeCN) 6 ](BF 4 ) 2 [27] ( 12 ) in which the D parameter (or B 2 0 parameter) was estimated to be +146.5 cm −1 from NEVPT2 calculations (+148.9 cm −1 from PHI fitting of the dc magnetic data) but with a smaller U eff value of 7.6 cm −1 .…”

Single molecule magnets of cobalt and zinc homo- and heterometallic coordination polymers prepared by a one-step synthetic procedure

“…This indicates that the systems have a large unquenched orbital contribution, which is characteristic of Co(II) ions in pseudo-octahedral coordination. 59,60,[62][63][64][65][66][67] When lowering temperature, the cT product slowly decreases to the minimum of 1.64 cm 3 K mol À1 observed at 2 K, which is mainly due to spin orbit coupling (SOC). For Co(II) ions in a distorted octahedral geometry the rst order SOC would be important and the experimental data have been sometimes tted with the corresponding Hamiltonian.…”

“…[67][68][69][70][71] Herein, we employed the later approach for sake of simplicity and to allow further comparison with published systems. 58,[60][61][62][63][64][65][66][67] This way, the ZFS Hamiltonian, as implemented in the PHI package (eqn (1)), was employed for the simultaneous t of the experimental susceptibility and magnetization curves.…”