Probing the Effects of Ligand Field and Coordination Geometry on Magnetic Anisotropy of Pentacoordinate Cobalt(II) Single-Ion Magnets

Abstract

In this work, the effects of ligand field strength as well as the metal coordination geometry on magnetic anisotropy of pentacoordinated Co complexes have been investigated using a combined experimental and theoretical approach. For that, a strategic design and synthesis of three pentacoordinate Co complexes [Co(bbp)Cl]·(MeOH) (1), [Co(bbp)Br]·(MeOH) (2), and [Co(bbp)(NCS)] (3) has been achieved by using the tridentate coordination environment of the ligand in conjunction with the accommodating terminal ligands (i.e., chloride, bromide, and thiocyanate). Detailed magnetic studies disclose the occurrence of slow magnetic relaxation behavior of Co centers with an easy-plane magnetic anisotropy. A quantitative estimation of ZFS parameters has been successfully performed by density functional theory (DFT) calculations. Both the sign and magnitude of ZFS parameters are prophesied well by this DFT method. The theoretical results also reveal that the α → β (SOMO-SOMO) excitation contributes almost entirely to the total ZFS values for all complexes. It is worth noting that the excitation pertaining to the most positive contribution to the ZFS parameter is the d → d excitation for complexes 1 and 2, whereas for complex 3 it is the d → d excitation.

Field-induced slow relaxation of magnetization in the S = 3/2 octahedral complexes trans-[Co{(OPPh2)(EPPh2)N}2(dmf)2], E = S, Se: effects of Co–Se vs. Co–S coordination

“…Similar effects, on the magnitude of the axial anisotropy due to the coordination of heavier halides, have also been established in tetrahedral [74][75][76][77][78][79][80] Co(II) complexes, in some instances imposing a concomitant change in the sign of D as well. 76,77 On the other hand, contrary to the above observations, lower axial anisotropy due to the coordination of heavier halides has been observed in squarepyramidal 81,82 and pentagonal bipyramidal 83 Co(II) complexes.…”

Field Induced Single Ion Magnetic Behaviour in Square-Pyramidal Cobalt(II) Complexes with Easy-Plane Magnetic Anisotropy

“…0.814 Å out of the {N(2),N(3),N(4),N(5)} plane in the direction of Cl(2). The two trans positioned N-Co-N angles are almost identical 135.99 (5) and 135.62(4)° for N3-Co1-N5 and N2-Co1-N4, respectively, and correspond to the ideal spy Keeping the above points in mind and following our interest in Co II based SIMs [16,17,20,21,24,27], we aimed to prepare low-coordinate Co II SIMs by using macrocyclic ligand 14-TMC and 12-TBC. Therefore in this paper we report the synthesis, structural characterization, and magnetization study of square-pyramidal Co II complexes [Co(14-TMC)Cl](BF 4 ) (1) and [Co(12-TBC)Cl](ClO 4 )•(MeCN) (2).…”

“…Recently, molecules comprising a single paramagnetic lanthanide or actinide metal centre have been reported to exhibit slow magnetic relaxation behaviour at low temperatures [4][5][6]. The substantial efforts have been given for the development of both lanthanides based [7][8][9][10] and transition metal based [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] single ion magnets (SIMs). During last few years, the efforts to rationally manipulate the magnetic anisotropy of single ion magnets have been increased [12].…”

“…The first example of Co II SIM was a pentacoordinate system having square-pyramidal geometry with bis(imino)pyridine pincer ligand in conjunction with two isothiocyanate ligands [25]. Thereafter several Co II based complexes with various coordinate systems have been explored for showing the single ion magnetic behaviour [11][12][13][14][15][16][17][20][21][22][23][24][27][28][29][30][31][32][33].…”

Field‐Induced Single‐Ion Magnetic Behavior in Two Mononuclear Cobalt(II) Complexes

“…Replacement of Br À by Cl À resulted in av ariation of magnetic anisotropy, owing to different s-/p-donating effects of Br À and Cl À ions. [15] Motivated by the impetust os ynthesize pentacoordinated cobalt(II) complexesw ith desired single-ion magnetic proper-ties, we designed an ew ligand:b is(1-chloroimidazo[1,5-a]pyridin-3-yl)pyridine (bcpp). The rigid N-tridentate backbone meets the requirement for tricoordination to the metal centers.…”