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Francesc Lloret

Publications and source records attributed to Francesc Lloret.

61 records · Page 4Linked to original sources
PubMed1997

Ferromagnetic Coupling between Copper(II) Centers through the Diamagnetic Zinc(II) Ion: Crystal Structure and Magnetic Properties of [Cu(2)Zn(Hdmg)(2)(dmg)(2)(H(2)O)].0.5H(2)dmg.H(2)O (H(2)dmg = Dimethylglyoxime).

A new heterotrinuclear complex of formula [Cu(2)Zn(Hdmg)(2)(dmg)(2)(H(2)O)].0.5H(2)dmg.H(2)O (C(18)H(34)Cu(2)N(9)O(11)Zn, 1) (H(2)dmg = dimethylglyoxime) has been synthesized and its crystal structure determined by single-crystal X-ray diffraction. It crystallizes in the triclinic system, space group P&onemacr;, with a = 11.414(1) Å, b = 11.992(3) Å, c =12.567(10) Å, alpha = 91.27(6) degrees, beta = 111.46(2) degrees, gamma = 112.24(2) degrees, and Z = 2. The structure consists of a chain of neutral [Cu(2)Zn(Hdmg)(2)(dmg)(2)(H(2)O)] trinuclear units and noncoordinated H(2)dmg and water molecules. The configuration around the zinc atom is distorted trigonal bipyramidal with four oximate oxygens from two [Cu(Hdmg)(dmg)](-) fragments (each one acting as a bidentate ligand through its deprotonated oximate oxygens in cis positions) occupying one axial and the three equatorial positions and an additional oximate oxygen from a symmetry-related [Cu(Hdmg)(dmg)](-) fragment filling the remaining axial position. The environment around Cu(1) and Cu(2) is distorted square pyramidal with four oximate nitrogen atoms building the equatorial plane. An oxygen atom [O(9)] from a water molecule and an oximate oxygen from a symmetry-related [Cu(Hdmg)(dmg)](-) fragment occupy the apical position of the square pyramids around Cu(1) and Cu(2), respectively. The trinuclear units are repeated through inversion centers standing at the middle of the Zn(1).Zn(1)(i) and Cu(2).Cu(2)(ii) vectors leading to a chain which runs parallel to the diagonal of the ac-plane. The Cu(1).Cu(2), Zn(1).Zn(1)(i), and Cu(2).Cu(2)(ii) separations are 5.506(2), 3.390(2), and 3.930(2) Å, respectively. 1 exhibits a characteristic ferromagnetic behavior with a continuous increase of the chi(M)T product as the temperature is lowered from 300 to 2.0 K. The field dependence of the magnetization at 2.0 K is consistent with a low-lying quintet state. The only efficient exchange pathways responsible for the overall ferromagnetic coupling in 1 are the diamagnetic zinc(II) ion and the out-of-plane double-oximato bridge, the magnitude of the magnetic coupling between the copper(II) ions through these bridging units being 3.9 and 5.1 cm(-)(1), respectively.

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PubMed1997

An Azide-Bridged Copper(II) Ferromagnetic Chain Compound Exhibiting Metamagnetic Behavior.

The one-dimensional chain complex [Cu(2)(&mgr;(2)-1,1-N(3))(2)(&mgr;(2)-1,3-NO(3))(2)(&mgr;(2)-1,3-Me(3)NCH(2)CO(2))(2)](n)() (1) contains three different bridge groups, &mgr;(2)-1,1-azide (end-on), &mgr;(2)-nitrate, and &mgr;(2)-syn,syn-carboxylate, arranged so that the azide and carboxylate groups bridge equatorially and dictate the intrachain magnetic behavior between the copper magnetic orbitals. Variable-temperature magnetic susceptibility studies at low field, and magnetization studies at variable field, reveal dominant intrachain ferromagnetism (J = 26 cm(-)(1)) but also much weaker interchain ferromagnetism (Θ = 2.3 K) and antiferromagnetism (J(eff) = -0.18 cm(-)(1)). The structure has been rationalized in terms of a layered magnetic model with antiferromagnetic coupling between ferromagnetically coupled layers, leading to metamagnetic behavior. The intrachain ferromagnetism is explained satisfactorily using extended Hückel molecular orbital calculations, which show clearly that orbital countercomplementarity exists on the part of the two magnetic bridge groups (azide and carboxylate), despite the very large azide bridge angle (119.5 degrees ).

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PubMed1996

Crystal Structures and Magnetic Properties of Novel [Ln(III)Cu(II)(4)] (Ln = Gd, Dy, Ho) Pentanuclear Complexes. Topology and Ferromagnetic Interaction in the Ln(III)-Cu(II) Pair.

The first pentanuclear complexes of formula {Dy[Cu(apox)](2)[Cu(apox)(H(2)O)](2)}[ClO(4)](3).7H(2)O (1), {Ho[Cu(apox)][Cu(apox)(H(2)O)](3)}[PF(6)](3).4.5H(2)O (2), {Gd[Cu(apox)](2)[Cu(apox)(H(2)O)](2)}[ClO(4)](3).7H(2)O (3) and {Gd[Cu(apox)][Cu(apox) (H(2)O)](3)}[PF(6)](3).4.5H(2)O (4) (H(2)apox = N,N'-bis(3-aminopropyl)oxamide) have been synthesized. The crystal structures of complexes 1 and 2 have been determined by X-ray diffraction methods. Complexes 3 and 4 are isostructural with 1 and 2, respectively. Crystallographic data are as follows: 1 and 3, monoclinic, space group C2/c and Z = 4, with a = 14.646(6) Å, b = 29.496(7) Å, c = 16.002(7) Å, and beta = 111.76(2) degrees for 1 and a = 14.523(6) Å, b = 29.441(6) Å, c = 15.925(8) Å, and beta = 111.90(4) degrees for 3; 2 and 4, triclinic, P&onemacr;, and Z = 2, with a = 14.346(2) Å, b = 14.454(2) Å, c = 18.107(4) Å, alpha = 90.95(2) degrees, beta = 110.75(2) degrees, and gamma = 106.77(2) degrees for 2 and a = 14.365(6) Å, b = 14.496(5) Å, c = 18.172(7) Å, alpha = 91.27(3) degrees, beta = 110.74(3) degrees, and gamma = 106.67(3) degrees for 4. A tripositive ion is present in these structures, the electroneutrality being achieved by three uncoordinated perchlorate (1) or hexafluorophosphate (2) anions. The lanthanide cations are eight-coordinate with a pseudo-square-antiprismatic environment formed by carbonyl oxygen atoms from two [Cu(apox)] and two Cu(apox)(H(2)O)] (1) and one [Cu(apox)] and three [Cu(apox)(H(2)O)] (2) bidentate ligands. The temperature dependence of the magnetic susceptibility of complexes 1-4 was investigated in the range 1.8-300 K. The ligand-field effect, as well as the mixing of the free-ion states in Dy(III) and Ho(III), make extremely difficult the analysis of the overall antiferromagnetic interaction which is observed for complexes 1 and 2. The magnetic susceptibility data for complexes 3 and 4 have shown that the ground-state spin for the [Gd(III)Cu(II)(4)] unit is S = 11/2, the Gd(III)-Cu(II) interaction being ferromagnetic with an interaction parameter J(GdCu) = 0.85 cm(-)(1) (the interaction Hamiltonian is of the form H = -JS(A).S(B)). The field dependence of the magnetization at 2 K of 3 and 4 confirms the nature of the ground state and of the Gd(III)-Cu(II) interaction. The influence of the topology and of the type of bridging ligand on the nature and magnitude of the magnetic interaction in the Gd(III)-Cu(II) pair is analyzed and discussed in light of available magnetostructural data.

Journal Article↗
PubMed1996

Through-Bond Exchange Coupling and Triplet Excitons in a Dinuclear Copper(II) Macrocyclic Complex.

The reaction of the bicyclic cryptand 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosan-5,6,14,15,22,23-hexone (1) with copper(II) leads to the dinuclear complex {1,10-bis(2-aminoethyl)-1,4,7,10,13,16-hexaazacyclooctadecane-5,6,14,15-tetronato(4-)}dicopper(II) (2). 2 crystallizes in the triclinic system (space group P&onemacr;, No. 2), with cell parameters a = 6.751(1) Å, b = 10.153(1) Å, c = 10.748(2) Å, alpha = 71.83(1) degrees, beta = 89.79(1) degrees, gamma = 73.56(1) degrees, and Z = 1. The structure is made up of centrosymmetric neutral dinuclear copper(II) units stacking along the a axis. Each copper(II) ion assumed a distorted-octahedral environment. The basal positions are occupied by four nitrogen atoms, two from deprotonated amide groups and two from the tertiary and primary amines; the apical positions are occupied by one amido nitrogen atom from the same dimer and one amido oxygen atom from a neighboring unit within the stack. The analysis of variable-temperature magnetic susceptibility data reveals the occurrence of a significant intramolecular antiferromagnetic interaction (J = -47 cm(-)(1)) in 2. The analysis of the exchange pathways by extended Hückel calculations shows a strong contribution of the N-C-C-N sigma bonds to the coupling between the two copper(II) ions. The triplet exciton type EPR spectrum of 2 allowed the evaluation of the interdimer interaction (J' approximately 10(-)(3) cm(-1)), a possible description of 2 as a magnetic alternating chain being ruled out.

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PubMed1996

Influence of the Peripheral Ligand Atoms on the Exchange Interaction in Oxalato-Bridged Nickel(II) Complexes: An Orbital Model. Crystal Structures and Magnetic Properties of (H(3)dien)(2)[Ni(2)(ox)(5)].12H(2)O and [Ni(2)(dien)(2)(H(2)O)(2)(ox)]Cl(2).

Two nickel(II) complexes of formula (H(3)dien)(2)[Ni(2)(ox)(5)].12H(2)O (1) and [Ni(2)(dien)(2)(H(2)O)(2)(ox)]Cl(2) (2) (dien = diethylenetriamine and ox = oxalate dianion) have been synthesized and characterized by single-crystal X-ray diffraction. 1 crystallizes in the orthorhombic system, space group Abnn, with a = 15.386(4) Å, b = 15.710(4) Å, c = 17.071(4) Å, and Z = 4. 2 crystallizes in the monoclinic system, space group P2(1)/c, with a = 10.579(1) Å, b = 7.258(1) Å, c = 13.326(1) Å, beta = 93.52(3) degrees, and Z = 2. The structures of 1 and 2 consist of dinuclear oxalato-bridged nickel(II) units which contain bidentate oxalate (1) and tridentate dien in the fac-conformation (2) as terminal ligands. Both features, oxalato as a peripheral ligand and dien in the fac-conformation (instead of its usual mer-conformation), are unprecedented in the coordination chemistry of nickel(II). The nickel atom is six-coordinated in both compounds, the chromophores being NiO(6) (1) and NiN(3)O(3) (2). The Ni-O(ox) bond distances at the bridge (2.072(4) Å in 1 and 2.11(1) and 2.125(9) Å in 2) are somewhat longer than those concerning the terminal oxalate (2.037(5) and 2.035(3) Å in 1). Magnetic susceptibility data of 1 and 2 in the temperature range 4.2-300 K show the occurrence of intramolecular antiferromagnetic coupling with J = -22.8 (1) and -28.8 (2) cm(-)(1) (J being the parameter of the exchange Hamiltonian H = -JS(A).S(B)). The observed value of -J in the investigated oxalato-bridged nickel(II) complexes, which can vary from 22 to 39 cm(-)(1), is strongly dependent on the nature of the donor atoms from the peripheral ligands. This influence has been analyzed and rationalized through extended Hückel calculations.

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