The magnet-like behavior can beobserved by slow relaxation of the magnetization below theblocking temperature. Since the discovery of SMMs in theearly 1990s, this assumption has formed the basis for theunderstanding of the origin of the anisotropic barrier.However, in recent years the development of novel lantha-nide-only SMMs that challenge and defy this theory pose anumber of questions:

A Polynuclear Lanthanide Single-Molecule Magnet with a Record

The impact of ligands upon topology and functionality of octacyanidometallate-based assemblies

We described the syntheses, crystal structures, and magnetic behavior of a novel series of heterometallic [Ni4M2] [M = Gd (1), Dy (2) and Y (3)] hexanuclear compounds afforded by the reaction of rare-earth(III) nitrate, nickel(II) acetate, and Schiff-base ligand 2-(2-hydroxy-3-methoxybenzylideneamino)phenol (H2L) in a mixture of ethanol and dichloromethane in the presence of triethylamine. Single-crystal X-ray diffraction measurements reveal that all three compounds have a metal core made up of two Ni2MO4 defective cubanes. The magnetic properties of all compounds have been studied. Solid-state direct-current magnetic susceptibility analyses demonstrate competing antiferromagnetic and ferromagnetic interactions within both compounds 1 and 3. Solid-state alternating-current magnetic susceptibility investigations show a frequency-dependent out-of-phase signal for compound 2 below 4 K, suggestive of slow magnetic relaxation.

Syntheses, structures, and magnetic analyses of a family of heterometallic hexanuclear [Ni4M2] (M = Gd, Dy, Y) compounds: observation of slow magnetic relaxation in the Dy(III) derivative.

The rhenium(IV) complex (NBu4)2[ReBr4(ox)] (1) (ox = oxalate and NBu4+ = tetra-n-butylammonium cation) has been prepared and its crystal structure determined by X-ray diffraction. The structure is made up of discrete [ReBr4(ox)]2– anions and bulky NBu4+ cations. Each [ReBr4(ox)]2– anion is surrounded by six NBu4+ cations, which preclude any significant intermolecular contact between the anionic entities, the shortest rhenium···rhenium distance being 9.373(1) A. Variable temperature dc and ac magnetic susceptibility measurements and field-dependent magnetization experiments on polycrystalline samples of 1 reveal the occurrence of highly anisotropic magnetically isolated Re(IV) centers (SRe = 3/2), which exhibit slow relaxation of the magnetization at very low temperatures in a dc field. Ac measurements conducted on a polycrystalline sample of the complex (NBu4)2[ReCl4(ox)] (2) [compound isostructural to 1 whose structure and dc magnetic susceptibility study were previously reported in Tomkiewicz, A.; Bartc...

Highly anisotropic rhenium(IV) complexes: new examples of mononuclear single-molecule magnets.

The aim and the scope of this review is to show the results of ten years of research following the first reports on magnetic and photomagnetic assemblies constructed from [M(CN)8]n–. It is illustrated on the basis of our own work as well as a wide range of studies carried out in numerous laboratories around the world. The diversity and evolution of topological and structural patterns is discussed alongside synthetic strategies, which led to the establishment of regular magnetostructural correlations in selected 3D systems. Different types of functionality observed in solid phases are presented with special attention devoted to tuning of magnetic properties by physical and chemical stimuli. Examples of advanced properties discovered in octacyanometallate-based magnetic materials comprise SMMs (single molecule magnets) and SCMs (single chain magnets), nonlinear effects MSHG (magnetization-induced second harmonic generation) and chirality, SCO (spin crossover) and luminescence. The potential of the development of octacyanometallate-based coordination assemblies towards addressable, multifunctional molecular materials for future application is discussed.

A Decade of Octacyanides in Polynuclear Molecular Materials

A new family of oxime-based hexanuclear manganese(III) single molecule magnets with high anisotropy energy barriers.

Salicylamidoxime was used to synthesize 13 new polynuclear Mn(III) complexes. We present the crystallographic structures, the magnetic susceptibility and the magnetization measurements of eight of them (1-8) with the general formula [Mn(6)O(2)(H(2)N-sao)(6)(L)(2)(solvent)(4-6)] (L = carboxylate, chloride, 2-cyanophenolate; solvent = H(2)O, MeOH, EtOH, py). These complexes consist of two trinuclear {Mn(III)(3)(μ(3)-O)(H(2)N-sao)(3)}(+) cationic units linked together via two oximate and two phenolate oxygen atoms. All behave as single-molecule magnets, with the spin ground state varying from 4 to 12 and anisotropy energy barriers from 24 to 86 K, the latter being as high as the present record barrier in the Mn(6) complexes. DFT calculations were performed to compute the exchange magnetic coupling constants J between the metallic ions and to provide an orbital interpretation of exchange. Our results are in line with previously reported results with the parent salicylaldoxime derivatives. The Mn-N-O-Mn torsion angle appears as the main parameter controlling the J values. The critical angle where the exchange coupling between two Mn(III) switches from antiferromagnetic to ferromagnetic is 27°, less than the one found in related complexes with salicylaldoxime (30°). We propose a structural classification of the {Mn(6)} complexes in four classes depending on the coordination of the axial carboxylate. The work points out the structural flexibility of such systems, their sensitivity to solvent effects and their ability to achieve high anisotropy energy barriers by simple desolvation.

Synthesis, crystal structure and magnetism of new salicylamidoxime-based hexanuclear manganese(III) single-molecule magnets

Compounds [Cr
 3
 III
 (μ3-O)(O2CPh)5(H2N-sao)(EtOH)2]·EtOH (1·EtOH) and [Cr
 3
 III
 (μ3-O)(O2CPh)3(H2N-pao)3]NO3·H2N-paoH·EtOH (2·NO3·H2N-paoH·EtOH) have been obtained either in a sequential one-pot, two-step procedure in which Cr(NO3)3·9H2O is first reacted with sodium benzoate in ethanol under reflux, followed by the addition of salicylamidoxime (H2N-saoH2) or pyridine-2-amidoxime (H2N-paoH), or in a one-step protocol starting from [Cr
 3
 III
 (μ3-O)(O2CPh)6(EtOH)3]NO3. They were characterized by single-crystal X-ray diffraction, magnetometry and EPR spectroscopy. Complexes 1 and 2 are derived from the parent complex [Cr
 3
 III
 (μ3-O)(O2CPh)6(EtOH)3]+ by replacement of one and three benzoate ligands, respectively, by oximate ligands. The salicylamidoximate and pyridine-2-amidoximate ligands display a tridentate coordination mode with the N–O oximate group bridging a pair of Cr atoms and the additional ligating atom substituting for an ethanol ligand of the parent complex. In both cases susceptibility, magnetization and EPR data reveal a S
 T = 1/2 ground state with a nearly isotropic g-tensor.

Adrian-Raul Tomsa

Papers

A new family of oxime-based hexanuclear manganese(III) single molecule magnets with high anisotropy energy barriers.

Synthesis, crystal structure and magnetism of new salicylamidoxime-based hexanuclear manganese(III) single-molecule magnets

Oxo-Centered Trinuclear Chromium(III) Complexes with Both Carboxylate and Amidoximate Ligands