Heterometallic Complexes Containing the NiII-LnIII-NiII Moiety—Structures and Magnetic Properties

This review summarizes the structural characteristics and magnetic properties of trinuclear complexes containing the NiII-LnIII-NiII moiety and also oligonuclear complexes and coordination polymers containing the same trinuclear moiety. The ligands used are mainly polydentate Schiff base ligands and reduced Schiff base ligands and, in some cases, oximato, β-diketonato, pyridyl ketone ligands and others. The compounds reported are restricted to those containing one, two and three oxygen atoms as bridges between the metal ions; examples of carboxylato and oximato bridging are also included due to structural similarity. The magnetic properties of the complexes range from ferro- to antiferromagnetic depending on the nature of the lanthanide ion.

Assembly of chiral 3d–4f wheel-like cluster complexes with achiral ligands: single-molecule magnetic behavior and magnetocaloric effect

With the help of perchlorate ions, chiral M₃Ln₃ wheel-like cluster complexes were constructed from achiral ligands, and showed single-molecule magnetic behavior and magnetocaloric effect.

Slow magnetic relaxation in Ni–Ln (Ln = Ce, Gd, Dy) dinuclear complexes

Unusual magnetic behaviour is observed in compounds with three Cl ligands in fac-mode coordination to dysprosium, cerium and even gadolinium.

Three different types of bridging ligands in a 3d-3d'-3d'' heterotrimetallic chain

A one-pot synthesis of a 3d-3d'-3d'' heterotrimetallic coordination polymer with double diphenoxido, single cyanido and bis-bidentate oxalate as alternating bridges which exhibits an overall antiferromagnetic behaviour has been developed.

Heterometallic Heptanuclear [Cu5Ln2] (Ln = Tb, Dy, and Ho) Single-Molecule Magnets Organized in One-Dimensional Coordination Polymeric Network

The reaction of a multisite coordination ligand, LH₃, with Cu(II) salts and Ln(NO₃)₃·nH₂O in a 1:2:1 stoichiometric ratio in the presence of triethylamine was found to afford a series of one-dimensional heterometallic [{Cu₅Ln₂(L)₂(μ₃-OH)₄(ClO₄)(NO₃)₃(OH₂)₅}(ClO₄)₂(H₂O)_x]_∞ [Ln = Tb(1), Dy(2) and Ho(3), x = 4.25, 5.5, and 5 for 1-3, respectively] coordination polymers. Complexes 1-3 have been characterized by single crystal X-ray crystallography. The detailed study of the magnetic properties has also been performed and compared with the parent [Cu₅Ln₂] molecular analogues. The ac susceptibility measurements for complexes 1-3 confirm their SMM behavior with the following characteristics: Δ_eff/k_B = 23.4 K, τ₀ = 1.1 × 10^-6 s and Δ_eff/k_B = 27.9 K, τ₀ = 6.6 × 10^-7 s under 0 and 1200 Oe dc fields, respectively for 1; Δ_eff/k_B = 8.3 K, τ₀ = 3.1 × 10^-6 s for 2 under 0 dc field. For 3, the fast QTM below 4 K prevents the estimation of the SMM energy barrier. Remarkably, the magnetic and SMM properties of the previously reported molecular [Cu₅Ln₂] analogues are preserved after their assembly in these coordination networks.

Bis-phenoxido and bis-acetato bridged heteronuclear {Co(III)Dy(III)} single molecule magnets with two slow relaxation branches

Two bis-μ-phenoxido-bis-μ-acetato heterobimetallic {Co(III)Dy(III)} complexes and , formulated as [Co(III)Dy(III)L(μ-OAc)2(NO3)2] derived from the comparable hexadentate Schiff bases N,N'-ethylenebis(3-ethoxysalicylaldimine) and N,N'-ethylenebis(3-methoxysalicylaldimine) were synthesized and X-ray structure analysis confirms their nearly identical structures. These are the first examples of bis(μ-phenoxido)-bis(μ-carboxylato) {Co(III)Dy(III)} systems. The AC susceptibility measurements show that both complexes exhibit a field-induced slow magnetic relaxation with two relaxation branches. While the high-frequency process spans the usual range of the relaxation time for analogous single molecule magnets (τ0 ∼ 10(-7) s), the low-frequency branch is as slow as τ ∼ 0.1 s at T = 1.9 K and B = 0.2 T.

N-HO and N-HCl supported 1D chains of heterobimetallic CuII/NiII-SnIV cocrystals

The Schiff base H₂L¹ [N,N'-ethylenebis(3-methoxysalicylaldimine)] or H₂L² [N,N'-ethylenebis(3-ethoxysalicylaldimine)] was reacted with MCl₂·xH₂O and SnCl₄·5H₂O to afford the supramolecular heterobimetallic systems (H₂ED)²⁺·2[ML]·[SnCl₆]^2- [M = Cu, L = L¹ (1), L = L² (2); M = Ni, L = L¹ (3), L = L² (4); ED = 1,2-ethylenediamine], whose structures were established by single crystal X-ray analyses. Each structure includes different entities, viz. a mononuclear [CuL]/[NiL] neutral complex (coformer), a hexachlorostannate dianion [SnCl₆]^2-, a 1,2-ethylenediammonium dication (H₂ED²⁺) and, only in 2 and 4, a methanol molecule. Based on the work of Grothe et al. (Cryst. Growth Des., 2016, 16, 3237-3243), compounds 1 and 3 are cocrystal salts, 2 and 4 are cocrystal salt solvates. The ionic pairs (H₂ED)²⁺·[SnCl₆]^2- in 1-4 are encapsulated by the Cu- or Ni-complexes, and stabilized by N-HO and one N-HCl bond interactions leading to infinite 1D chains. The antimicrobial studies of 1-4 against yeasts (C. albicans and S. cerevisiae) and Gram-positive (S. aureus and E. faecalis) and -negative bacteria (P. aeruginosa and E. coli) indicate that the Ni₂Sn systems (3 and 4) are more active than the analogous Cu₂Sn ones (1 and 2).

Synthesis, magnetism and spectral studies of six defective dicubane tetranuclear {M4O6} (M = NiII, CoII, ZnII) and three trinuclear CdII complexes with polydentate Schiff base ligands

Six defective dicubane face-shared and three trinuclear complexes are synthesized. The magnetic behaviors of Ni^II/Co^II complexes and fluorescence properties of Zn^II and Cd^II are studied.

Supramolecular 3d–4f single-molecule magnet architectures

Cooperative hydrogen bonds are key to the formation of nanosized {[{Ln^III}{H₂O⊂CrIII3LnIII6}]₂(H₂O)}-type single-molecule magnets, templated by a central water triad.

The exceptionally rich coordination chemistry generated by Schiff-base ligands derived from o-vanillin

Recent and relevant examples of homo- and heterometallic complexes generated by Schiff base ligands derived from o-vanillin, as well as their properties, are discussed.