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Biomedical subjects

Fernando Palacio

Publications and source records attributed to Fernando Palacio.

8 recordsLinked to original sources
PubMed2006

Co3(RL)2(hfac)6 ladder complex of 5-[4-(N-tert-butyl-N-aminoxyl)phenyl]pyrimidine.

5-[4-(N-tert-butyl-N-aminoxyl)phenyl]pyridimine (4NITPhPyrim = RL) forms a 1-D ladder polymer complex with Co(hfac)2 of stoichiometry Co3(RL)2(hfac)6, having antiparallel [Co(II)RL]n linear chains (rails) that are cross-linked by Pyrim-Co(hfac)2-Pyrim rungs. The magnetic behavior above 100 K is consistent with contributions from one high-spin Co(II) ion (the cross-link, S = 3/2) plus two Co-ON units with strongly antiferromagnetic (AFM) metal-radical exchange (each S = 1). The chiT data show an AFM downturn as the temperature drops. Assuming weak exchange along chain portions of the polymer due to poor spin polarization across the phenyl-pyrimidine bond in RL, a linear three-spin (S = 1, 3/2, and 1) fit to the T > 18 K data yields an AFM cross-linker (rung) effective exchange of J(CL)/k = (-)5.3 K = (-)3.7 cm(-)(1). Superexchange (sigma-orbital overlap) is a likely mechanism for the effective AFM exchange between CoON and Co spin sites in the three-spin groupings.

Journal Article↗
PubMed2005

A new bimetallic intercalated 3-D assembly magnet [{(323)Ni}3{FeIII(CN)6}2]n x 12nH2O (323 = N,N'-bis(3-aminopropyl) ethylenediamine): an unprecedented concomitant presence of meridional and facial arrangment of ferricyanide anion.

A novel molecular based magnet of three-dimensional (3-D) cyanide-bridged bimetallic assembly, [{(323)Ni}3{FeIII(CN)6}2]n x 2nH2O where 323 = N,N'-bis(3-aminopropyl) ethylenediamine, was synthesized and structurally characterized. The compound crystallizes in the orthorhombic space group Pbca with a = 15.6560 A, b = 15.2910 A, c = 50.9120 A, and Z = 8. The assembly has two intercalated 3-D networks created by FeIII-CN-NiII-NC-FeIII linkages. The ferricyanide anion adopts both facial and meridional arrangements through the linkage. Interesting magnetic properties including 3-dimensional magnetic ordering were revealed. The assembly displays 3-dimensional magnetic ordering below 5.2 +/- 0.1 K and field-induced magnetic behavior below 5.1 +/- 0.1 K and above 1.15 +/-0.05 kOe.

Journal Article↗
PubMed2003

Manganese(II) and copper(II) hexafluoroacetylacetonate 1:1 complexes with 5-(4-[N-tert-butyl-N-aminoxyl]phenyl)pyrimidine: regiochemical parity analysis for exchange behavior of complexes between radicals and paramagnetic cations.

Mn(hfac)(2) and Cu(hfac)(2) form coordination complexes with 5-(4-[N-tert-butyl-N-aminoxyl]phenyl)pyrimidine, PyrimPh-NIT. (Mn[PyrimPh-NIT](hfac)(2))(2) and (Cu[PyrimPh-NIT](hfac)(2))(2), 1 and 2, respectively, are cyclic M(2)L(2) dimers that exhibit strong exchange coupling between the coordinated paramagnetic dication (M) and nitroxide (NIT) unit. The M-NIT exchange is strongly antiferromagnetic (AFM) in 1 and strongly ferromagnetic (FM) in 2. Magnetic susceptibility measurements for 1 were fitted to an AFM spin pairing model with J/k = -0.25 K between Mn-NIT spin sites units. Complex 2 also exhibits AFM spin pairing between S = 1 Cu-NIT spin units that is somewhat field dependent at low temperature. The fit of corrected paramagnetic susceptibility chi(T) to an AFM spin pairing model at 200 Oe yields J/k = (-)3.8 K, quite similar to earlier measurements at 1000 Oe yielding J/k = (-)5.0 K. At 1.40 K, the magnetization of 2 does not approach saturation until somewhat above 170 kOe, giving an S-shaped curve; at 0.55 K, the magnetization curve shows steps characteristic of field-induced crossover between the S = 0 ground state and excited spin states. From the steps in the 0.55 K data, we estimate J/k = (-)3.8-4.0 K for 2, in good agreement with the analysis of chi(T).

Journal Article↗
PubMed2002

Structure and exchange in silicon-linked tetraradicals.

The EPR spectroscopy, crystallography, and magnetic susceptibility of tetrakis(N-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)silane and tetrakis(4-N-tert-butyl-N-aminoxylphenyl)silane show that silicon acts as a weak intramolecular exchange linker for polynitroxides, although both tetraradicals show onset of inter-spin exchange at reduced temperatures.

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