Interplay of Magnetic Exchange Interactions and NiSNi Bond Angles in Polynuclear Nickel(II) Complexes

Abstract

The ability of bridging thiophenolate groups (RS -) to transmit magnetic exchange interactions between paramagnetic Ni(II) ions has been examined. Specific attention was paid to complexes with large Ni-SR-Ni angles. For this purpose, dinuclear [Ni2Land trinuclear [Ni3L 2 (OAc)2][BPh4]2 (3), where H2L 1 and H2L 2 represent 24-membered macrocyclic amino-thiophenol ligands, were prepared and fully characterized by IR-and UV-vis spectroscopy, X-ray crystallography, static magnetization M measurements and high-field electron spin resonance (HF-ESR). The dinuclear complex 2 has a central N3Ni2(-S)2(-OAc)Ni2N3 core with a mean Ni-S-Ni angle of 92°. The macrocycle L 2 supports a trinuclear complex 3, with distorted octahedral N2O2S2 and N2O3S coordination environments for one central and two terminal Ni(II) ions, respectively. The Ni-S-Ni angles are at 132.8° and 133.5°. We find that the variation of the bond angles has a very strong impact on the magnetic properties of the Ni complexes. In the case of the Ni2-complex, temperature T and magnetic field B dependencies of M reveal a ferromagnetic coupling J = -29 cm -1 between two Ni(II) ions (H = JS1S2). HF-ESR measurements yield a negative axial magnetic anisotropy (D < 0) which implies a bistable (easy axis) magnetic ground state. In contrast, for the Ni3-complex we find an appreciable antiferromagnetic coupling J' = 97 cm -1 between the Ni(II) ions and a positive axial magnetic anisotropy (D > 0) which implies an easy plane situation.

Magnetic Anisotropy of Cr(III) Ions in Polymeric Oxalate Complexes as Revealed by HF-ESR Spectroscopy

“…3. A transfer of the spectral weight to lower magnetic field at low temperatures revealed a negative axial magnetic anisotropy of the molecule (parameter D < 0) in both complexes [11,4], in accord with the self-orientation of the particles during measurements in a high magnetic field and the presence of an "easy" axis of anisotropy. …”

“…1 and 2. The relation between the axial ZFS parameter, D, and the magnetic anisotropy gap, ∆, is: [4,5] …”

Preparation and Characterization of Dinuclear Nickel(II) Complexes Containing N3Ni(μ1, 3‐SO3R)2(μ‐RCN4)NiN3 Cores: Crystal Structures and Magnetic Properties

“…A previous high-field EPR study has shown that the D values for Ni II 2 complexes supported by the N 6 S 2 macrocycle have a negative sign and are on the order of 0.5-1.0 cm -1 . [22] Nevertheless, the value of J is unambiguous and represents an accurate measure of the magnetic coupling in these complexes.…”

Hexaaza‐dithia Macrocycles Containing Pendant Methoxyethyl Groups: Synthesis and Characterization of Mono and Dinuclear Nickel Complexes

“…In contrast to H 2 L1, which supports mono-and dinuclear Ni II complexes, the ligand H 2 L3 was found to form a trinuclear Ni II complex, due to participation of the 2-hydroxyethyl substituents in the coordination of the metal ions. [15] Herein, the synthesis of the ligands H 2 L4 and H 2 L5 carrying pendant 2-methoxyethyl substituents [16] is described and their ability to form mono-and dinuclear Ni complexes is demonstrated. The crystallographic analyses of two complexes provide insights into the effects of the conversion of the 2-hydroxyethyl to 2-methoxyethyl groups on the structural features.…”