Peripheral site modification in a family of dinuclear [Dy2(hynad)2-6(NO3)0-6(sol)0-2]0/2- single-molecule magnets bearing a {Dy2(µ-OR)2}4+ diamond-shaped core and exhibiting dissimilar magnetic dynamics.

The first use of the organic chelate N-hydroxy-1,8-naphthalimide (hynadH) in DyIII chemistry has unveiled access to a synthetic 'playground' composed of four new dinuclear complexes, all of which possess the same planar {Dy2(µ-OR)2}4+ diamond-shaped core, resulting from the bridging and chelating capacity of the hynad- groups. The structural stability of the central {Dy2} core has allowed for the modulation of the peripheral coordination sites of the metal ions, and specifically the NO3-/hynad- ratio of capping groups, thus affording the compounds [Dy2(hynad)2(NO3)4(DMF)2] (1), (Me4N)2[Dy2(hynad)2(NO3)6] (2), [Dy2(hynad)4(NO3)2(H2O)2] (3), and [Dy2(hynad)6(H2O)2] (4). Because of the chemical and structural modifications in the series 1-4, the DyIII coordination polyhedra are also dissimilar, comprising the muffin (1 and 3), tetradecahedral (2), and spherical tricapped trigonal prismatic (4) geometries. Complexes 1, 2, and 4 exhibit a ferromagnetic response at low temperatures, while 3 is antiferromagnetically coupled. All compounds exhibit out-of-phase (χ''M) ac signals as a function of ac frequency and temperature, thus behaving as single-molecule magnets (SMMs), in the absence or presence of applied dc fields. Interestingly, the hynad--rich and nitrato-free complex 4, demonstrates the largest energy barrier (Ueff = 69.62(1) K) for the magnetization reversal which is attributed to the presence of the two axial triangular faces of the spherical tricapped trigonal prism by the negatively charged O-atoms of the hynad- ligands.

Slow Magnetization Relaxation in a Family of Triangular {CoIII 2 LnIII } Clusters: The Effect of Diamagnetic CoIII Ions on the LnIII Magnetic Dynamics.

The first use of the Schiff base chelate N-naphthalidene-o-aminophenol (naphH2 ) in Co/Ln chemistry has afforded a family of isostructural [CoIII 2 LnIII (OMe)2 (naph)2 (O2 CMe)3 (MeOH)2 ] (Ln=Tb, Dy and Er) complexes, revealing a rare {CoIII 2 Ln(µ3 -OMe)}8+ triangular core composed of two diamagnetic CoIII ions and a 4f-ion with slightly distorted square antiprismatic geometry. Alternating current (ac) magnetic susceptibility studies revealed that {Co2 Dy}, and its magnetic diluted analogue {Co2 Dy0.05 Y0.95 }, behave as mononuclear single-molecule magnets (SMMs) with similar energy barriers for the magnetization reversal, Ueff , of ~85-90 K. SMM properties were also detected for {Co2 Er}, with the compound exhibiting a Ueff of 18.7 K under an applied magnetic field of 800 Oe. To interpret the experimental magnetic results, ab initio CASSCF/RASSI-SO and DFT calculations were performed as a means of exploring the single-ion characteristics of LnIII ions and comprehend the role of the diamagnetic CoIII ions in the magnetization relaxation of the three heterometallic compounds.

A family of mono-, di-, and tetranuclear DyIII complexes bearing the ligand 2,6-diacetylpyridine bis(picolinoylhydrazone) and exhibiting slow relaxation of magnetization.

The systematic investigation of the general reaction scheme DyIII/X-/LH2, where X- = Cl-, CF3SO3-, ClO4-, MeCO2-, and LH2 is the pocket-type ligand 2,6-diacetylpyridine bis(picolinoylhydrazone), resulting from the condensation of 2,6-diacetylpyridine with picolinic acid hydrazide, has led to a new family of mono-, di-, and tetranuclear metal complexes of the formulae [DyCl2(LH2)(MeOH)]Cl (1), [Dy2(O3SCF3)2(LH)2(MeOH)1.42(H2O)0.58](O3SCF3)2 (2), [Dy2(LH)2(MeOH)2(H2O)2](ClO4)4 (3), and [Dy4(OH)2(O2CMe)6(L)2] (4), respectively. The organic chelate undergoes metal-assisted amide-iminol tautomerism and adopts the neutral zwitterionic, and single- and double-deprotonated forms, respectively, upon coordination with the metal center(s). Interestingly, the different forms of the ligand LH2/LH-/L2- act independently as penta-, hexa-, and heptadentate, either as single-chelating or chelating and bridging, thus yielding new DyIII compounds of various nuclearities and different magnetic properties. All complexes 1-4 exhibit frequency-dependent, out-of-phase (χ''M) tails of signals in zero external dc field, characteristic of the onset of quantum tunnelling of magnetization. Attempts to suppress the tunnelling through the application of an external dc field were mostly successful in the case of complex 1, where entirely visible peaks of χ''M have been observed and rendered possible the fit of the data to the Arrhenius equation, thus yielding the parameters: Ueff = 10.9(1) K and τ0 = 1.9(1) × 10-6 s, where Ueff is the effective energy barrier for the magnetization reversal and τ0 is the pre-exponential factor. The combined results demonstrate the ability of pyridyl-bis(acylhydrazone) ligands to yield chemically, structurally, and magnetically interesting compounds through their rich interconversion between various amide-iminol resonance forms.