Antonio S. Florencio

Bio: Antonio S. Florencio is an academic researcher from Federal Fluminense University. The author has contributed to research in topics: Crystal structure & Density functional theory. The author has an hindex of 4, co-authored 6 publications receiving 61 citations.

New copper(II)-radical one dimensional chain: Synthesis, crystal structure, EPR, magnetic properties and DFT calculations.

Abstract: The novel chain compound [Cu(Phtfac)2(NITpPy)]n (where NITpPy = 4-pyridyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and Phtfac = 4,4,4-trifluoro-1-phenylbutane-1,3-dione) was synthesized and characterized structurally, magnetically and by EPR. The compound contains two non equivalent Cu(II) ions, Cu1 and Cu2, located at inversion centers and bridged by a NITpPy ligand coordinating Cu1 through the pyridine donor atom, and Cu2 through a N–O group, resulting in a head-to-head chain structure. The chain exhibits an unusual spin topology with two alternating pairs of magnetic coupling constants. The magnetic behavior was modeled considering a 16-membered ring with alternating exchange couplings. The best fit parameters indicate a ferromagnetic (J1 = 29.4 cm−1), and antiferromagnetic (J2 = −4.6 cm−1) couplings and an average g = 2.05, corresponding to a ground state with three parallel and one anti-parallel spin for each Cu2NITpPy2 unit. DFT calculations allowed assigning the ferromagnetic coupling to Cu-O-NITpPy and the antiferromagnetic coupling to Cu-NPy-NITpPy. Single crystal EPR spectra display only one resonance for most field orientations, as a consequence of the collapse of the signals of the different spins produced by the exchange interactions. The observed g-tensor of this resonance is related to those expected for the Cu(II) and radical ions. Comparison of this compound with other Cu-NIT radicals chains bearing different substituents in the organic radicals, highlights that the β-diketonate ligand plays an important role in determining the final architecture. Moreover, we show how a knowledge of the spin density distribution in the initial building blocks is essential to rationalize the magnetic behavior of the resulting product.

Synthesis, structural and magnetic characterization of a new copper(II)-nitronyl nitroxide radical complex

Abstract: -2-(4-piridil)-4,4,5,5-tetrametilimidazolina-1-oxil-3-oxido). Os estudos magneticos sugerem que neste complexo existe uma competicao entreinteracoes ferromagneticas e antiferromagneticas. A interacao ferromagnetica pode ser explicadacom base na ortogonalidade dos orbitais magneticos envolvidos.In this work we describe the structure and the magnetic properties of a new copper(II)-NITcomplex, where NIT stands for nitronyl nitroxide radical. This was achieved using(NBu

A cobalt pyrenylnitronylnitroxide single-chain magnet with high coercivity and record blocking temperature.

Abstract: Coordination of a [Co(hfac)2] moiety (hfac=hexafluoroacetylacetonate) with a nitronylnitroxide radical linked to bulky, rigid pyrene (PyrNN) gives a helical 1:1 chain complex, in which both oxygen atoms of the radical NO. groups are bonded to CoII ions with strong antiferromagnetic exchange. The complex shows single-chain magnet (SCM) behavior with frequency-dependent magnetic susceptibility, field-cooled and zero-field-cooled susceptibility divergence with a high blocking temperature of around 14 K (a record among SCMs), and hysteresis with a very large coercivity of 32 kOe at 8 K. The magnetic behavior is partly related to good chain isolation induced by the large pyrene units. Two magnetic relaxation processes have been observed, a slower one attributable to longer, and a faster one attributable to short chains. No evidence of magnetic ordering has been found.

Glauber slow dynamics of the magnetization in a molecular Ising chain

Abstract: The slow dynamics (10^-6 s - 10^4 s) of the magnetization in the paramagnetic phase, predicted by Glauber for 1d Ising ferromagnets, has been observed with ac susceptibility and SQUID magnetometry measurements in a molecular chain comprising alternating Co{2+} spins and organic radical spins strongly antiferromagnetically coupled. An Arrhenius behavior with activation energy Delta=152 K has been observed for ten decades of relaxation time and found to be consistent with the Glauber model. We have extended this model to take into account the ferrimagnetic nature of the chain as well as its helicoidal structure.

New Synthetic Route toward Heterometallic 3d–3d′ and 3d–4f Single-Molecule Magnets. The First CoII–MnIII Heterometallic Complex

Abstract: Four tetranuclear heterometallic complexes, [CoII2Mn2III(dpm)4(MeO)6] (1) and [LnIII2MnIII2(dpm)6(MeO)6(MeOH)n], where Ln = Gd (2, n = 2), Tb (3, n = 2), and Dy (4, n = 0), have been obtained follo...

Magnetic Mn and Co complexes with a large polycyclic aromatic substituted nitronylnitroxide.

Abstract: 2-(1'-Pyrenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (PyrNN) was reacted with M(hfac){sub 2} (M = Mn(II) and Co(II), hfac = hexafluoracetylacetonate) to give two isostructural ML{sub 2} stoichiometry M(hfac){sub 2}(PyrNN){sub 2} complexes and a ML stoichiometry one-dimensional (1-D) polymer chain complex [Mn(hfac){sub 2}(PyrNN)]. The ML{sub 2} complexes have similar crystal structures with monoclinic unit cells, in which one NO unit from each PyrNN ligand is bonded to the transition metal on cis vertices of a distorted octahedron. The major magnetic interactions are intracomplex metal-to-radical exchange (J), and intermolecular exchange across a close contact between the uncoordinated NO units (J'). For M = Mn(II) an approximate chain model fit gives g = 2.0, J = (-)125 cm{sup -1} and J' = (-)49 cm{sup -1}; for M = Co(II), g = 2.4, J = (-)180 cm{sup -1}, and J' = (-)70 cm{sup -1}. Hybrid density functional theory (DFT) computations modeling the intermolecular exchange by using only the radical units across the close contact are in good accord with the estimated values of J'. The chain type complex structure shows solvent incorporation for overall structure [Mn(hfac){sub 2}(PyrNN)]{sub n} {center_dot} 0.5(CHCl{sub 3}) {center_dot} 0.5(C{sub 7}H{sub 16}). Both NO groups of the PyrNN ligand are complexed to form helical chains, withmore » very strong metal to radical antiferromagnetic exchange that gives overall ferrimagnetic behavior.« less