PubMed Health⌕ Search

Biomedical subjects

Ramon Vicente

Publications and source records attributed to Ramon Vicente.

24 records · Page 2Linked to original sources
PubMed1997

Magnetic Studies on &mgr;-Azido Polynuclear Nickel(II) Compounds with the 222-tet Ligand. Crystal Structure of (&mgr;-N(3))(2)[Ni(222-tet)](2)(BPh(4))(2) (222-tet = Triethylenetetramine) and EXAFS Structural Characterization of the Triangular Compounds (&mgr;-N(3))(3)[Ni(222-tet)](3)(X)(3) (X = PF(6)(-), ClO(4)(-)).

The nickel(II) dinuclear 1,3-azido-bridged compound (&mgr;-N(3))(2)[Ni(222-tet)](2)(BPh(4))(2) (1) and the trinuclear compounds (&mgr;-N(3))(3)[Ni(3)(222-tet)(3)](PF(6))(3) (2) and (&mgr;-N(3))(3)[Ni(3)(222-tet)(3)](ClO(4))(3) (3) were synthesized and characterized. 222-tet is the tetraaminate ligand triethylenetetramine. The crystal structure of 1 was solved by X-ray diffraction. 1 crystallizes in the monoclinic system: space group P2(1)/n, a = 10.639(4) Å, b = 19.770(7) Å, c = 13.609(6) Å, beta = 97.78(3) degrees, Z = 2, formula C(60)H(76)B(2)N(14)Ni(2). In the absence of single crystals of 2 and 3, we carried out an EXAFS study of 1-3 at the nickel K-edge, using compound 1 as a model, in order to obtain structural information for compounds 2 and 3. The analysis of XANES and EXAFS spectra of compounds 1-3 reveals the occurrence of azido-bridged trinuclear nickel(II) compounds for 2 and 3 with Ni-Ni separations of 5.16 and 5.12 Å, respectively. Each nickel(II) atom is placed in an octahedral NiN(6) environment: four nitrogen atoms of the amine and two nitrogen atoms of two azido bridges. The magnetic properties of the three compounds were studied by susceptibility measurements at variable temperatures (300-4 K). From the spin Hamiltonian H = -JS(1)S(2), the calculated J value for 1 is -83.6 cm(-)(1), in good agreement with the expected value. From the spin Hamiltonian H = -J(1,2)(S(1)S(2) + S(1)S(3)) - J(3)(S(2)S(3)), the obtained J values are J(1,2) = -72(3) cm(-)(1), J(3) = -36(3) cm(-)(1) for 2 and J(1,2) = -60.3(3) cm(-)(1), J(3) = -29.4(2) cm(-)(1) for 3.

Journal Article↗
PubMed1997

A New Family of High-Dimensional Molecular Magnets Built from the Manganese-Azido System. Syntheses, Structures, and Magnetic Characterization of Two New Ferro-Antiferromagnetic Two-Dimensional Complexes.

Two new compounds in the series of general formula [Mn(L)(2)(N(3))(2)](n)() in which L = 4-cyanopyridine (1) or 3-acetylpyridine (2) have been obtained and structurally and magnetically characterized. Both compounds crystallize in the monoclinic system, space group P2(1)/a, formula [C(12)H(8)MnN(10)] with a = 13.286(4) Å, b = 8.340(3) Å, c = 13.579(4) Å, beta = 90.55(2) degrees, and Z = 4 for compound 1 and space group P2(1)/c, formula [C(14)H(14)MnN(8)O(2)] with a = 11.843(4) Å, b = 9.550(3) Å, c = 14.998(5) Å, beta = 105.99(3) degrees, and Z = 4 for compound 2. The two compounds show a similar arrangement of alternating end-to-end and end-on azido bridges between the manganese atoms, giving magnetically alternated ferro-antiferromagnetic two-dimensional compounds. The pyridyl ligands coordinated to the axial sites stick out above and below the 2-D sheets, and intersheet pi-pi interactions are formed between the pyridyl ligands, playing a role in the structural differences. The low-temperature magnetic properties of 1 and 2, together with those of the previously reported compounds with L = pyridine (3), 4-acetylpyridine (4), and ethyl isonicotinate (5), are reported. Magnetic ordering and spontaneous magnetization is achieved at T(C) = 18, 16, 40, 28, and 16 K for 1-5, respectively.

Journal Article↗
PubMed1997

Structure and Magnetic Behavior of a New 1-D Compound with Simultaneous End-On Azido and Carboxylato Bridges. Unexpected Strong Ferromagnetic Coupling for a Cu-N-Cu Bond Angle of 111.9 degrees as a Consequence of Ligand HOMOs Countercomplementarity.

The X-ray structure of the &mgr;-carboxylate-&mgr;(1,1)-azido-bridged compound {[Cu(Hpht)(N(3))].H(2)O}(n)() has been determined (Hpht = hydrogen phthalate). Crystal data: formula C(8)H(7)CuN(3)O(5), monoclinic, P2(1)/m (No. 11), a = 7.383(3) Å, b = 6.568(4) Å, c = 10.659(4) Å, beta = 93.38(3) degrees, Z = 2. The compound is found to be a system formed by chains of copper atoms bridged simultaneously by syn-syn carboxylato and end-on azido bridges. The copper chains are linked by a second carboxylato bridge, giving a 2-D compound. Magnetic measurements indicate strong ferromagnetic coupling, which affords a good example of unexpected magnetic properties due to the countercomplementarity of the superexchange pathways of the two ligands.

Journal Article↗
PubMed1996

Synthesis and Structural Characterization of [Mn(ethyl isonicotinate)(2)(N(3))(2)](n)(), a Two-Dimensional Alternating Ferromagnetic-Antiferromagnetic Compound. Magnetostructural Correlations for the End-to-End Pseudohalide-Manganese System.

Three compounds with formula [Mn(L)(2)(N(3))(2)](n)(), in which L is 4-acpy = 4-acetylpyridine (1), Etinc = ethyl isonicotinate (2), and py = pyridine (3), have been studied from the magnetic point of view. The new compound [Mn(L)(2)(N(3))(2)](n)() (2) crystallizes in the monoclinic system, space group P2(1)/a (No. 14), formula [C(16)H(18)MnN(8)O(4)], with a = 15.176(5) Å, b = 9.060(3) Å, c = 15.760(6) Å, beta = 111.62(3) degrees, and Z = 4. Compounds 1 and 2 are two-dimensional systems, whereas 3 is a 3-D compound. Compound 2 shows ferromagnetic Mn(2)(N(3))(2) dimeric entities linked antiferromagnetically to the four neighboring dimeric entities by four end-to-end azido bridges, leading to an alternate ferromagnetic-antiferromagnetic two-dimensional compound. MO calculations have been performed to study the superexchange pathway for the manganese 1,3-azido system.

Journal Article↗
PubMed1996

A Novel Pentadentate Coordination Mode for the Carbonato Bridge: Synthesis, Crystal Structure, and Magnetic Behavior of (&mgr;(3)-CO(3))[Ni(3)(Medpt)(3)(NCS)(4)], a New Trinuclear Nickel(II) Carbonato-Bridged Complex with Strong Antiferromagnetic Coupling.

The trinuclear complex (&mgr;(3)-CO(3))[Ni(3)(Medpt)(3)(NCS)(4)] was obtained by reaction of basic solutions of nickel(II), Medpt (bis(3aminopropyl)methylamine) and thiocyanate ligand with atmospheric CO(2) or by simple reaction with carbonate anion. (&mgr;(3)-CO(3))[Ni(3)(Medpt)(3)(NCS)(4)] crystallizes in the triclinic system, space group P&onemacr;, with a = 12.107(5) Å, b = 12.535(7) Å, c = 16.169(9) Å, alpha = 102.69(5) degrees, beta = 92.91(5) degrees, gamma = 118.01(4) degrees, Z = 2, and R = 0.043. The three nickel atoms are asymmetrically bridged by one pentadentate carbonato ligand, which shows a novel coordination mode. The (&mgr;(3)-CO(3))[Ni(3)(Medpt)(3)(NCS)(4)] compound shows a very strong antiferromagnetic coupling. Fit as irregular triangular arrangement gave J(1) = -88.4, J(2) = -57.7, and J(3) = -9.6 cm(-)(1), which is the strongest AF coupling observed to date for Ni(3) compounds. The magnetic behavior of the carbonato bridge is discussed.

Journal Article↗