Effects of the Exchange Coupling on Dynamic Properties in a Series of CoGdCo Complexes

Abstract

Reaction of 2-hydroxy3-methoxybenzaldehyde (o-vanillin) with 1,1,1-tris(aminomethyl)ethane, Me-C-(CH 2 NH 2 ) 3 , or with N,N′,N′′-trimethylphosphorothioic trihydrazide, P(S)[NMe-NH 2 ] 3 , yields two tripodal LH 3 and L 1 H 3 ligands which are able to give cationic heterotrinuclear [LCoGdCoL] + or [L 1 CoGdCoL 1 ] + complexes. The Co II ions are coordinated to these deprotonated ligands in the inner N 3 O 3 site, while the Gd III ion is linked to three deprotonated phenoxo oxygen atoms of two anionic [LCo] − or [L 1 Co] − units. Air oxidation of these trinuclear complexes does not yield complexes associating Co III and Gd III ions. With the first ligand, the structurally characterized resulting complex is the neutral mononuclear LCo III compound, while in the second case, oxidation of the Co II ions turned out to be impossible. The [L 1 CoLnCoL 1 ] + complexes behave as single-molecule magnets with effective energy barriers for the reversal of magnetization varying from U eff = 51.3 K, τ o = 2 × 10 −6 s for the yttrium complex to U eff = 29.5, 29.4, 27.4 K and τ o = 1.3 × 10 −7 , 1.47 × 10 −7 , 1.50 × 10 −7 s for the gadolinium ones, depending on the used counteranions. The energy decrease is compensated by the suppression of quantum tunneling of magnetization in absence of applied field, thanks to the introduction of a ferromagnetic Co−Gd interaction. Current work also shows that uncritical use of conventional spin Hamiltonians, based on quenched orbital momenta, can be misleading and that ab initio calculations are indispensable for establishing the picture of real magnetic interaction. Ab initio calculations show that the Co II sites in the investigated compounds possess large unquenched orbital moments due to the first-order spin−orbit coupling resulting in strongly axial magnetic anisotropy. Although the Co II ions are not axial enough for showing slow relaxation of magnetization by themselves, blocking barriers of exchange type are obtained thanks to the exchange interaction with Gd III ions.

Large easy-axis magnetic anisotropy in a series of trigonal prismatic mononuclear cobalt(ii) complexes with zero-field hidden single-molecule magnet behaviour: the important role of the distortion of the coordination sphere and intermolecular interactions in the slow relaxation

“…18,21 In light of the above considerations, the aim of this work is fourfold: (i) to confirm that complexes 1-4 show large axial magnetic anisotropy. The previous results of Ruiz and coworkers 10 and Costes 22 and co-workers for Co II and Co II Y III Co II complexes (the latter can be considered as formed by two almost isolated mononuclear complexes) with CoN 6 and CoN 3 O 3 trigonal prismatic coordination environments, respectively, bearing similar tripodal ligands to L, showed negative D values of −72 cm −1 and −38.8 cm −1 , respectively; (ii) to analyse how the change of the anion alters the Co II coordination sphere and, consequently, the axial magnetic anisotropy. Likewise, we want to support the above indicated theoretical variation of the anisotropy with the distortion of the TPR-6 coordination sphere; (iii) to study how the change of the anion affects the crystal packing and the relaxation dynamic, focusing specially on the role played by the dipolar interactions, and (iv) to unequivocally determine the sign and magnitude of D for the tetragonally compressed octahedral compound 5 by a combination of experimental and theoretical methods, including HFEPR and FIRMS spectroscopies.…”

Dynamic Metal Exchange between a Metalloid Silver Cluster and Silver(I) Thiolate

“…Scientific research on metalloid clusters has a long history, and significant efforts have been made on manipulation over the structures (e.g., metal doping and ligand exchange) and the properties (e.g., optical and catalytic properties) of nanoparticles. − However, research on metalloid clusters has generally focused on structure determination and property investigations, while analysis on interactions between a metalloid cluster and foreign species just began to receive attention in the past decade. − Previous studies on such interactions mainly include the following two aspects: (i) the metal exchange process between a metalloid cluster (as precursors) and heterometal (representing a different metal element from the metalloid cluster) thiolate in the environment ,− and (ii) the intercluster reactions between different types of metalloid clusters in the same environment. − Specifically, for the metal exchange process, heterometal substitution is always determined by the relative energies of the doping sites and the characteristic of heterometals because of their different electron affinities. In this context, a fundamental understanding of the interaction between a metalloid cluster and the homometal thiolate still remains challenging.…”

Magnetic materials based on heterometallic CrII/III–LnIII complexes

“…199 Additionally, the judicious choice of ligands with specific coordination pockets for Cr III as well as Ln III centres could lead to the synthesis of interesting dinuclear/trinuclear heterometallic complexes which would provide a better platform to understand and manipulate the magnetization dynamics, rather than aesthetically pleasing bigger complexes often characterized by low U eff values. 109,[200][201][202][203][204][205][206] In fact, to date, the SMM properties of the Cr II -Ln III -based systems and surface-grafted Cr III -Ln III -based systems are yet to be explored. Therefore, stabilization of such systems through chemical modification also could unleash numerous potential avenues in heterometallic SMM chemistry.…”