Field induced single ion magnet behavior in CoII complexes in a distorted square pyramidal geometry.

We report three CoII-based complexes with the general formula [CoII(L)(X)2] by changing the halide/pseudo-halide ions [X = NCSe (1SeCN); Cl (2Cl) and Br (3Br)]. The obtained τ5 and CShM values confirm a distorted square pyramidal geometry around the CoII ion in all these complexes. In these three complexes, the central CoII ion is situated above the basal plane of the square pyramidal geometry. The extent of distortion from the ideal SPY-5 geometry differs upon changing the coordinating halide/pseudo-halide ion in these complexes. This essentially results in the alteration of the anisotropic parameter D and hence impacts the magnetic properties in these complexes. This phenomenon has been corroborated with the aid of theoretical investigations. All these complexes display field-induced SIM behaviour with magnetic relaxation occurring through a combination of processes depending on the applied dc magnetic field values and dilution.

Azide-Coordination in Homometallic Dinuclear Lanthanide(III) Complexes Containing Nonequivalent Lanthanide Metal Ions: Zero-Field SMM Behavior in the Dysprosium Analogue.

A series of homometallic dinuclear lanthanide complexes containing nonequivalent lanthanide metal centers [Ln2(LH2)(LH)(CH3OH)(N3)]·xMeOH·yH2O [1, Ln = DyIII, x = 0, y = 2; 2, Ln = TbIII, x = 1, y = 1] have been synthesized [LH4 = 6-((bis(2-hydroxyethyl)amino)-N'-(2-hydroxybenzylidene)picolinohydrazide] and characterized. The dinuclear assembly contains two different types of nine-coordinated lanthanide centers, because the nonequivalent binding of the azide co-ligand as well as the varying coordination of the deprotonated Schiff base ligand. Detailed magnetic studies have been performed on the complexes 1 and 2. Complex 1 and its diluted analogue (15%) are zero-field SMMs with effective energy barriers (Ueff) of magnetization reversal equal to 59(3) K and 66(3) K and relaxation times of τ0 = 10(4) × 10-6 s and 10(4) × 10-8 s, respectively. On the other hand, complex 2 shows a field-induced SMM behavior. Combined ab initio and density functional theory calculations were performed to explain the experimental findings and to unravel the nature of the magnetic anisotropy, exchange-coupled spectra, and magnetic exchange interactions between the two lanthanide centers.

Solid-State Near-Infrared Circularly Polarized Luminescence from Chiral YbIII -Single-Molecule Magnet.

A field-induced chiral YbIII Single-Molecule Magnet (SMM) displayed an unprecedented near-infrared circularly polarized luminescence (NIR-CPL) in the solid-state. The bridging bis(1,10-phenantro[5,6b])tetrathiafulvalene triad (L) allowed an efficient sensitization of the NIR 2 F5/2 →2 F7/2 emission while the NIR-CPL is associated to the f-f transitions of the YbIII ion bearing chiral ß-diketonate derived-camphorate ancillary ligands.

Slow Magnetic Relaxation in Dinuclear CoIIYIII Complexes.

Four new dinuclear complexes, [Co(µ-L)(µ-CCl3COO)Y(NO3)2]·2CHCl3·CH3CN·2H2O (1), [Co(µ-L)(µ-CH3COO)Y(NO3)2]·CH3CN (2), [Co(µ-L)(µ-PhCOO)Y(NO3)2]·3CH3CN·2H2O (3), and [Co(µ-L)(µ-tBuCOO)Y(NO3)2]·CHCl3·2H2O (4), having a CoIIYIII core, have been synthesized by employing a ferrocene based compartmental ligand which was synthesized by the reaction of diacetyl ferrocene with hydrazine hydrate followed by a condensation reaction with o-vanillin. A general synthetic protocol was employed to synthesize complexes 1-4, where the metallic core was kept the same with changing the bridging carboxylate groups. In all the complexes, the main structural motif is kept similar by only slightly varying the substitution on the bridging acetate groups. This variation has resulted in a small but subtle influence on the magnetic relaxation of all these four compounds. Ab initio CASSCF/NEVPT2 calculations were carried out to assess the effect of the different substitutions of the bridging ligands on the magnetic anisotropy parameters and on orbital arrangements. Ab initio calculations yield a very large positive D value, which is consistent with the geometry around the CoII ion and easy plane anisotropy (gxx, gyy > gzz), with the order of the calculated D in the range of 72.4 to 91.7 cm-1 being estimated in this set of complexes. To ascertain the sign of zero-field splitting in these complexes, EPR spectra were recorded, which support the sign of D values estimated from ab initio calculations.

Structural and magnetic investigations of a binuclear coordination compound of dysprosium(iii) dinitrobenzoate.

A centro-symmetric binuclear compound of formula [Dy(L)·(CH3COO)2·(H2O)2]2 (1) was isolated from the reaction between the 2,4-dinitrobenzoate anion (L) and the tris(acetate) of Dy(iii). Single crystal diffraction studies reveal a µ1-κ2,η1:η1 chelating binding mode of L while the binuclear compound is formed by the two bridging (µ2-κ3,η1:η2) acetate anions. The nona-coordinated sphere of each Dy(iii) ion is filled with a chelating (κ2,η1:η1) acetate anion and two terminal water molecules. Static magnetic measurements combined with ab initio SA-CASSCF/RASSI-SO calculations lead to two intramolecular competitive interactions i.e. ferromagnetic exchange interactions (0.04 cm-1) and antiferromagnetic dipolar interactions (-0.5 cm-1). Finally, dynamic magnetic measurements revealed a Single-Molecule Magnet behaviour in a zero-applied magnetic field with an effective energy barrier Δ = 21.5(2) cm-1 and τ0 = 7(3) × 10-6 s through Orbach and Quantum Tunnelling of the Magnetization relaxation mechanisms.

Field-Induced Dysprosium Single-Molecule Magnet Based on a Redox-Active Fused 1,10-Phenanthroline-Tetrathiafulvalene-1,10-Phenanthroline Bridging Triad.

Tetrathiafulvalene and 1,10-phenanthroline moieties present, respectively remarkable redox-active and complexation activities. In this work, we investigated the coordination reaction between the bis(1,10-phenanthro[5,6-b])tetrathiafulvalene triad (L) and the Dy(hfac)3·2H2O metallo precursor. The resulting {[Dy2(hfac)6(L)]·CH2Cl2·C6H14}3 (1) dinuclear complex showed a crystal structure in which the triad L bridged two terminal Dy(hfac)3 units and the supramolecular co-planar arrangement of the triads is driven by donor-acceptor interactions. The frequency dependence of the out-of-phase component of the magnetic susceptibility highlights three distinct maxima under a 2000 Oe static applied magnetic field, a sign that 1 displays a Single-Molecule Magnet (SMM) behavior with multiple magnetic relaxations. Ab initio calculations rationalized the Ising character of the magnetic anisotropy of the DyIII ions and showed that the main anisotropy axes are perpendicular to the co-planar arrangement of the triads. Single-crystal rotating magnetometry confirms the orientation of the main magnetic axis. Finally combining structural analysis and probability of magnetic relaxation pathways through Quantum Tunneling of the Magnetization (QTM) vs. excited states (Orbach), each DyIII center has been attributed to one of the three observed magnetic relaxation times. Such coordination compound can be considered as an ideal candidate to perform redox-magnetic switching.