A heteroleptic diradical Cr(iii) complex with extended spin delocalization and large intramolecular magnetic exchange

Successive chemical reductions of the heteroleptic complex [(tpy)Cr III(tphz)] 3+(tpy = terpyridine; tphz = tetrapyridophenazine) give rise to the mono- and di-radical redox isomers, [(tpy)Cr III(tphz? -)] 2+and [(tpy? -)Cr III(tphz? -)] +, respectively. As designed, the optimized overlap of the involved magnetic orbitals leads to extremely strong magnetic interactions between theS= 3/2 metal ion andS= 1/2 radical spins, affording well isolatedS T= 1 andS T= 1/2 ground states at room temperature. </p

Using Redox-Active πbridging Ligand as a Control Switch of Intramolecular Magnetic Interactions

Intramolecular magnetic interactions in the dinuclear complexes [(tpy)­Ni­(tphz)­Ni­(tpy)]^<i>n</i>+ (<i>n</i> = 4, 3, and 2; tpy, terpyridine; tphz, tetrapyridophenazine) were tailored by changing the oxidation state of the pyrazine-based bridging ligand. While its neutral form mediates a weak antiferromagnetic (AF) coupling between the two <i>S</i> = 1 Ni­(II), its reduced form, tphz^•–, promotes a remarkably large ferromagnetic exchange of +214(5) K with Ni­(II) spins. Reducing twice the bridging ligand affords weak Ni–Ni interactions, in marked contrast to the Co­(II) analogue. Those experimental results, supported by a careful examination of the involved orbitals, provide a clear understanding of the factors which govern strength and sign of the magnetic exchange through an aromatic bridging ligand, a prerequisite for the rational design of strongly coupled molecular systems and high <i>T</i>_C molecule-based magnets

A remarkably unsymmetric hexairon core embraced by two high-symmetry tripodal oligo-α-pyridylamido ligands

Oligo-α-pyridylamides offer an appealing route to polyiron complexes with short Fe-Fe separations and large room temperature magnetic moments. A derivative of tris(2‐aminoethyl)amine (H6tren) containing three oligo-α-pyridylamine branches and thirteen nitrogen donors (H6L) reacts with [Fe2(Mes)4] to yield an organic nanocage built up by two tripodal ligands with interdigitated branches (HMes = mesitylene). The nanocage has crystallographic D3 symmetry but hosts a remarkably unsymmetric hexairon-oxo core, with a central Fe5(μ5-O) square pyramid, two oxygen donors bridging basal sites, and an additional Fe center residing in one of the two tren-like pockets. Bond Valence Sum (BVS) analysis, Density Functional Theory (DFT) calculations, and electrochemical data were then used to establish the protonation state of oxygen atoms and the formal oxidation states of the metals. To this purpose, a specialized set of BVS parameters was devised for Fe2+-N3- bonds with nitrogen donors of oligo-α-pyridylamides. This allowed us to formulate the compound as [Fe6O2(OH)(H3L)L], with nominally four FeII and two FeIII ions. Mössbauer spectra indicate that the compound contains two unique FeII sites, identified as a pair of closely spaced hydroxo-bridged metal ions in the central Fe5(μ5-O) pyramid, and a substantially valence-delocalized FeII2FeIII2 unit. Broken-symmetry DFT calculations predict strong ferromagnetic coupling between the two iron(II) ions, leading to a local S = 4 state that persists to room temperature and explaining the large magnetic moment measured at 300 K. The compound behaves as a single-molecule magnet, with magnetization dynamics detectable in zero static field and dominated by an Orbach-like mechanism with Ueff/kB = 49(2) K and τ0 = 4(2)·10−10 s

A low spin manganese(IV) nitride single molecule magnet

Structural, spectroscopic and magnetic methods have been used to characterize the tris(carbene) borate compound PhB(MesIm)(3)Mn equivalent to N as a four-coordinate manganese(IV) complex with a low spin (S = 1/2) configuration. The slow relaxation of the magnetization in this complex, i.e. its single-molecule magnet (SMM) properties, is revealed under an applied dc field. Multireference quantum mechanical calculations indicate that this SMM behavior originates from an anisotropic ground doublet stabilized by spin-orbit coupling. Consistent theoretical and experiment data show that the resulting magnetization dynamics in this system is dominated by ground state quantum tunneling, while its temperature dependence is influenced by Raman relaxation

Cyanomethylene-bis(phosphonate)-Based Lanthanide Complexes: Structural, Photophysical, and Magnetic Investigations

10 pagesInternational audienceThe syntheses, structural investigations, magnetic and photophysical properties of a series of 10 lanthanide mononuclear complexes, containing the heteroditopic ligand cyanomethylene-bis(5,5-dimethyl-2-oxo-1,3,2λ5-dioxa-phosphorinane) (L), are described. The crystallographic analyses indicate two structural types: in the first one, [LnIII(L)3(H2O)2]*H2O (Ln = La, Pr, Nd), the metal ions are eight-coordinated within a square antiprism geometry, while the second one, [LnIII(L)3(H2O)]*8H2O (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er), contains seven-coordinated LnIII ions within distorted monocapped trigonal prisms...

Discrete versus Chain Assembly: Hexacyanometallate Linkers and Macrocyclic {3d–4f} Single-Molecule Magnet Building Blocks

International audienc

Coexistence of long-range antiferromagnetic order and slow relaxation of the magnetization in the first lanthanide complex of a 1,2,4-benzotriazinyl radical

The first lanthanide complex of a 1,2,4-benzotriazinyl radical (1), Dy(1)(tbacac)3 (2, tbacac = 2,2,6,6-tetramethyl-3,5-heptane-dionato), was synthesised and found to have an antiferromagnetically ordered ground state with a metamagnetic phase diagram and a critical field of 0.91 T at 1.85 K. The application of a small dc field revealed the single-molecule magnet behaviour of 2, illustrating the coexistence of long-range antiferromagnetic order and slow relaxation of the magnetization.peerReviewe

Using Redox-Active πbridging Ligand as a Control Switch of Intramolecular Magnetic Interactions

Intramolecular magnetic interactions in the dinuclear complexes [(tpy)Ni(tphz)Ni(tpy)]n+ (n = 4, 3, and 2; tpy, terpyridine; tphz, tetrapyridophenazine) were tailored by changing the oxidation state of the pyrazine-based bridging ligand. While its neutral form mediates a weak antiferromagnetic (AF) coupling between the two S = 1 Ni(II), its reduced form, tphz•-, promotes a remarkably large ferromagnetic exchange of +214(5) K with Ni(II) spins. Reducing twice the bridging ligand affords weak Ni-Ni interactions, in marked contrast to the Co(II) analogue. Those experimental results, supported by a careful examination of the involved orbitals, provide a clear understanding of the factors which govern strength and sign of the magnetic exchange through an aromatic bridging ligand, a prerequisite for the rational design of strongly coupled molecular systems and high TC molecule-based magnets.</p

Enantiopure versus Racemic Mixture in Reversible, Two-Step, Single-Crystal-to-Single-Crystal Transformations of Copper(II) Complexes

International audienceThe reaction of chiral sodium complexes, 11[Na(SvalmetH)]·H2O (1-S) and 1 1[Na(R-valmetH)]·H2O (1-R), withcopper(II) acetate affords chiral one-dimensional coordination polymers with the formulas 1 1[Cu(S-valmet)(H2O)]·H2O(2-S) and 1 1[Cu(R-valmet)(H2O)]·H2O (2-R) (R/S-valmetH2 are Schiff base proligands resulting from the condensation reactions between o-vanillin and R/S-methionine). The copper ions are connected by the carboxylato groups belonging tothe amino-acid moieties, resulting in infinite chains showing syn-anti out-of-plane bridging mode....

Spin-state modulation of molecular Fe III complexes via inclusion in halogen-bonded supramolecular networks

The cationic complex [Fe(qsal)] (Hqsal = N-(8-quinolyl)salicylaldimine) is encapsulated in anionic halogen-bonded 1D and 2D networks derived from sym-triiodotrifluorobenzene, [(CFI)Cl] and [(CFI)I]. Structural analysis and magnetic measurements show that the spin-state of this complex can be modulated by its inclusion in supramolecular host frameworks.Matériaux Moléculaires Ferroelectriques (et Magnétiques