Solvent-induced structural diversity in tetranuclear Ni(ii) Schiff-base complexes: the first Ni₄single-molecule magnet with a defective dicubane-like topology

Abstract

Two tetranuclear Ni complexes, namely [Ni(L)(CHOH)(HO)]·CHOH (1) and (PrNH)[Ni(L)(CHCOO)] (2, PrN = tripropylamine), were synthesized from a tridentate Schiff base ligand HL (2-[(E)-(2-hydroxybenzylidene)amino]phenol) and Ni(CHCOO)·4HO, using different solvents and their ratios (CHOH and/or CHCl). The prepared Ni complexes are of different structural types, involving an NiO cubane-like core (1) and NiO defective dicubane-like core (2), with all the Ni atoms hexacoordinated. The complexes were characterized by elemental analysis, FT-IR spectroscopy, variable temperature and field magnetic measurements, and single crystal X-ray analysis. The DFT and CASSCF/NEVPT2 theoretical calculations were utilized to reveal information about the isotropic exchange parameters (J) and single-ion zero-field splitting parameters (D, E). The variable temperature magnetic data suggested the competition of the antiferromagnetic and ferromagnetic intracluster interactions in compound 1, which is in contrast to compound 2, where all intracluster interactions are ferromagnetic resulting in the ground spin state S = 4 with an easy-axis type of anisotropy quantified by the axial zero-field splitting parameter D = -0.81 cm. This resulted in the observation of a field-induced slow-relaxation of magnetization (U = 3.3-6.7 K), which means that the complex 2 represents the first Ni single-molecule magnet with the defective dicubane-like topology.

Magnetic Anisotropy and Field‐induced Slow Relaxation of Magnetization in Tetracoordinate CoII Compound [Co(CH3‐im)2Cl2]

“…The other strategy involves deliberate tuning of magnetic anisotropy. Again, this is not straightforward for polynuclear complexes due to different mutual orientations of local D -tensor components depending on several conditions (e.g., cluster topology, differences in compositions of the coordination polyhedra implying different types of anisotropy) and interplay between the magnetic coupling and anisotropy [7]. Nevertheless, if we consider a special category of SMMs with one paramagnetic center, so called single-ion magnets (SIMs), then the deliberate modulation of the magnetic anisotropy is easier and depends reasonably on the topology and donor atom constitution of the coordination polyhedron [2].…”

Tetranuclear Ni(ii) and Co(ii) Schiff-base complexes with an M4O6 defective dicubane-like core: zero-field SMM behavior in the cobalt analogue

“…In our previous work, 11 we reported on the preparation of two Ni 4 compounds involving the H 2 L ligand:…”

“…Recently, we have reported on two tetranuclear nickel(II) compounds containing a tridentate Schiff base ligand H 2 L = 2-{(E)- [(2-hydroxyphenyl)imino]methyl}phenol with cubane and defective dicubane-like topologies and significantly different magnetic behaviours. 11 In the cubane-based complex, [Ni 4 (L) 4 (CH 3 OH) 3 (H 2 O)]ÁCH 3 OH, the competing ferro-and antiferromagnetic interactions led to the zero spin ground state, but the compound with the defective dicubane topology, (Pr 3 NH) 2 [Ni 4 (L) 4 (CH 3 COO) 2 ], exhibited ferromagnetic coupling between the central atoms and slow relaxation of magnetization in the presence of an external magnetic field. As a continuation of our ongoing study of compounds with defective dicubane topology with use of the H 2 L-type of tridentate Schiff base ligands, herein we report on the preparation of two isostructural compounds with the general formula [M II 4 (L) 4 (CH 3 OH) 2 ] (M = Ni (1), Co (2)).…”

Polynuclear ampyrone based 3d coordination clusters

“…Schiff base ligands are of particular interest due to their ease of synthesis and multiple coordination sites, thus have been extensively used for the synthesis of polynuclear CCs. [22][23][24][25][26][27][28] Ampyrone, also known as 4-aminoantipyrine, is a pyrazole derivative that has a keto group at position 5 and is substituted at position 4 by an amino group (A, Scheme 1). This organic scaffold has been used for the synthesis of dihydrotestosterone products, 29 whilst its derivatives, exhibit cycotoxic, 30 antimicrobial 31 or anagesic 32 activity, similar bioactivity to ampicillin and streptomycin, 33 and has been used to produce redox active Ru CCs, 34 hydrogen bonded framewoks, 35 fluorescent chemo sensors for F -36 and Cu 2+ /F -37 recognition, selective probes for Al 3+ and cysteine detection, 38 and pigments.…”