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Paul Rey

Publications and source records attributed to Paul Rey.

7 recordsLinked to original sources
PubMed2006

An unprecedented asymmetric end-on azido-bridged copper(II) imino nitroxide complex: structure, magnetic properties, and density functional theory analysis.

The dinuclear copper(II) complex [Cu2(mu(1,1)-N3)2(im-2py)2(N3)2] [im-2py = 2-(2-pyridyl)-4,4,5,5-tetramethylimidazolinyl-1-oxy] has been prepared and structurally characterized. The crystal structure consists of a dinuclear unit in which the Cu(II) ions are bridged by two azido ions in a end-on asymmetric fashion and the imino nitroxide radicals are chelating by the two imino N atoms. Accordingly, the magnetic susceptibility data were analyzed considering a linear spin-coupling scheme rad(1)-Cu(2)-Cu(3)-rad(4) (with Si = 1/2, i = 1-4), where the Heisenberg spin Hamiltonian assumes the general form -2Sigma(i)<(j)S(i)S(j). Considering only first-neighbor spin-coupling constants (J13 = J24 = J14 = 0), magnetic susceptibility measurements show that the copper(II) imino nitroxide rad-Cu-(Cu-rad)(rad-Cu)-Cu-rad exchange coupling is ferromagnetic and large (J12 = J34 = J1 > +190 cm(-1)), as is expected for copper imino nitroxide species, and the copper-copper (rad)-Cu-Cu-(rad) coupling through the asymmetric double end-on azide bridges appeared antiferromagnetic and rather large [J23 = J2 = -43(2) cm(-1)]. By contrast, a density functional theory analysis of the system through the computation of broken-symmetry-state energies resulted in J2 approximately 0 cm(-1). This apparent paradox is resolved by introducing a second-neighbor rad-(Cu)-Cu-(rad)(rad)-Cu-(Cu)-rad spin-coupling constant J13 = J24 = J3, which turns out to be antiferromagnetic both experimentally (when J2 is set equal to zero) and computationally.

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PubMed2006

Pyrimidinyl nitronyl nitroxides.

The chemistry of 2,2,4,4-substituted pentane derivatives has been investigated with the aim of providing a flexible and versatile synthetic route to pyrimidinyl nitronyl nitroxides, in which the bis-N-oxy fragment is incorporated in a six-membered ring. The synthesis of 2,4-diamino-2,4-dimethylpentane and 2,4-bis(hydroxylamino)-2,4-dimethylpentane, convenient precursors of these nitroxides, is described and full characterization of a series of pyrimidinyl nitronyl nitroxides is reported, along with a preliminary study of their coordination properties.

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PubMed2002

Synthesis, structures, and magnetic and optical properties of a series of europium(III) and gadolinium(III) complexes with chelating nitronyl and imino nitroxide free radicals.

This paper reports the synthesis, structures, and magnetic and optical properties of a series of gadolinium(III) (1a-4a) and europium(III) (1b-4b) complexes with nitronyl or imino nitroxide radicals. The crystal structures of compounds 1a and 1b consist of [Ln(III)(radical)(2)(NO(3))(3)] entities in which the gadolinium(III) (1a) or europium(III) ion (1b) is 10-coordinated to two nitronyl nitroxide radicals and three nitrato ligands. The crystal structures of compounds 2a-4a and 2b-4b consist of [Ln(III)(hfac)(3)(radical)] entities in which the gadolinium(III) (2a-4a) or europium(III) ion (2b-4b) is 8-coordinated to one nitronyl (2a and 2b) or one imino (3a, 4a and 3b, 4b) nitroxide radical and three hexafluoroacetylacetonato ligands. The gadolinium(III) complexes (1a-4a) are isostructural with their europium(III) analogues (1b-4b). The magnetic properties of the gadolinium complexes were studied. Along the series 1a-4a only compound 2a exhibits a ferromagnetic Gd(III)-radical coupling (J(Gd-rad) = +1.7 cm(-1)), while for the others this coupling is antiferromagnetic (1a: J(Gd-rad1) = -4.05 cm(-1) and J(Gd-rad2) = -0.80 cm(-1); 3a: J(Gd-rad) = -2.6 cm(-1); 4a: J(Gd-rad) = -1.9 cm(-1)). The first full luminescence spectra of lanthanide complexes with free radical ligands are reported between 650 and 1200 nm. The rich vibronic structure in luminescence and absorption spectra indicates that several excited states define the absorption spectra between 400 and 800 nm. Qualitative trends can be established between magnetic ground state properties and the energies and fine structure of the title compounds.

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PubMed2002

Synthesis, structures, and magnetic properties of a series of lanthanum(III) and gadolinium(III) complexes with chelating benzimidazole-substituted nitronyl nitroxide free radicals. Evidence for antiferromagnetic Gd(III)-radical interactions.

This paper reports the synthesis, crystal structures, and magnetic properties of a series of lanthanide complexes with nitronyl nitroxide radicals of general formula [[Ln(III)(radical)(4)] x (ClO(4))(3) x (H(2)O)(x) x (THF)(y)] (1-4) and [Ln(III)(radical)(2)(NO(3))(3)] (5, 6) [Ln = La (compounds 1, 3, 5) or Gd (compounds 2, 4, and 6); radical = 2-(2'-benzymidazolyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITBzImH, compounds 1, 2, 5, 6) or 2-[2'-[(6'-methyl)benzymidazolyl]]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITMeBzImH, compounds 3, 4)]. (1) C(64)H(88)Cl(3)LaN(16)O(24), fw = 1710.76, orthorhombic, Fddd, a = 11.0682(8) A, b = 34.240(3) A, c = 42.787(3) A, V = 16215(2) A(3), Z = 8, R = 0.0876, R(w) = 0.2336. (2) C(64)H(88)Cl(3)GdN(16)O(24), fw = 1729.10, tetragonal, P 4 macro 2c, a = 16.0682(4) A, b = 16.0682(4) A, c = 18.7190(6) A, V = 4833.0(2) A(3), R = 0.0732, R(w) = 0.2218. (3) C(68)H(94)Cl(3)LaN(16)O(23), fw = 1742.80, tetragonal, P 4 macro 2(1)m, a = 21.125(3) A, b = 21.125(3) A, c = 10.938(2) A, V = 4881.5(14) A(3), R = 0.1017, R(w) = 0.3126. (5) C(28)H(34)LaN(11)O(13), fw = 871.57, orthorhombic, Pna2(1), a = 19.5002(12) A, b = 13.0582(8) A, c = 14.5741(9) A, V = 3711.1(4) A(3), R = 0.0331, R(w) = 0.1146. (6) C(28)H(34)GdN(11)O(13), fw = 889.91, orthorhombic, Pna2(1), a = 19.1831(10) A, b = 13.1600(7) A, c = 14.4107(7) A, V = 3638.0(3) A(3), Z = 4, R = 0.0206, R(w) = 0.0625. Compounds 1-4 consist of [M(III)(radical)(4)](3+) cations, uncoordinated perchlorate anions, THF, and water crystallization molecules. In these complexes, the coordination number around the lanthanide ion is eight, and the polyhedron is either a distorted dodecahedron (1) or a distorted cube (2, 3). The crystal structures of 5 and 6 consist of independent [M(III)(radical)(2)(NO(3))(3)] entities in which the lanthanide is ten-coordinated and has a distorted bicapped square antiprism coordination polyhedron. For the lanthanum(III) complexes, the temperature dependence of the magnetic susceptibility indicates that radical-radical magnetic interactions are negligible either for compounds 1 and 3, while for compound 5 it is simulated considering dimers of weakly antiferromagnetically coupled radicals (J(rad-rad) = -1.1 cm(-1)). In the case of the gadolinium(III) compounds (2, 4, 6), each magnetic behavior gives unambiguous evidence of antiferromagnetic Gd(III)-radical interaction (2, J(Gd-rad) = -1.8 cm(-1); 4, J(Gd-rad) = -3.8 cm(-1); 6, J(Gd-rad1) = -4.05 cm(-1) and J(Gd-rad2) = -0.80 cm(-1)), in contrast to the ferromagnetic case generally observed. The nature of the Gd(III)-radical interaction is explained in relation to the donor strength of the free radical ligand.

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PubMed1998

Proximate Nitroxide Ligands in the Coordination Spheres of Manganese(II) and Nickel(II) Ions. Precursors for High-Dimensional Molecular Magnetic Materials.

The chelating nitroxide ligands 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-3-oxide-1-oxy (NITPy, 1), 2-(2-imidazolyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-3-oxide-1-oxy (NITImH, 2), and 2-(2-benzimidazolyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-3-oxide-1-oxy (NITBzImH, 3) and some of their transition metal complexes (Mn(II), Ni(II), Zn(II)) have been prepared and characterized by X-ray diffraction techniques and magnetic susceptibility measurements. All complexes are four- (or three-) spin systems where the metal coordination sphere is free of ancillary ligands because of the chelate effect which enforces the coordination of the oxyl group. The fac or mer nature of these species depends on the metal ions and on the steric demand of the ligand. It has been found that crystal packing is an important driving force toward the fac modification when steric requirements are not important. Crystal packing is probably also the cause of the noncentrosymmetric space group observed for the derivatives of NITPy. For the Zn(II) complex of NITImH, a moderate inter-nitroxide interaction within the metal coordination sphere of -14 cm(-)(1) is estimated. However, due to the modification of the spin distribution upon complexation, this interaction does not play a major role in the other complexes, where strong antiferromagnetic metal-nitroxide interactions (H = -2JS(i).S(j), -111 < J < -53 cm(-)(1)) are operative. The derivatives of NITImH are precursors of extended species which would be obtained by deprotonation of the ligand.

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PubMed1998

1D Manganese(II) Derivatives of an Imidazole-Substituted Nitronyl Nitroxide. An Approach toward Molecular Magnetic Materials of High Dimensionality.

Extended linear complexes of manganese(II) with a bis-chelating nitronyl nitroxide ligand, 2-(2-imidazolato)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-3-oxide-1-oxy (NITIm), have been prepared where metallic and organic spin carriers alternate. Depending on the deprotonating agent, the solvent, and the counteranion, the species [Mn(NITIm)(H(2)O)(2)]CH(3)COO, 1, [Mn(NITIm)(DMSO)(2)]BPh(4), 2, [Mn(NITIm)(H(2)O)(ImH)]NO(3), 3, and [Mn(NITIm)(NITImH)]ClO(4), 4, have been obtained, which differ by the additional ligands completing the metal coordination sphere. Complexes 1-3 are cis isomers and 4 is found as the mer modification; in all compounds, one observes a regular alternation of Lambda and Delta metal environments. Their magnetic properties are similar, with Mn(II)-nitroxide interactions J approximately -45 cm(-)(1) (H = -2JS(i)().S(j)()), and they display weak ferromagnetic properties below 5 K. Canting of the manganese ions is responsible for these properties. Relevant crystallographic parameters are as follows: 1, space group Fdd2, a = 16.713(1), b = 40.111(3), c = 9.735(1), Z = 16; 2, space group Pca2(1), a = 30.328(3), b = 13.422(1), c = 9.589(1), Z = 4; 3, space group P2(1)/c, a = 9.787(2), b = 22.973(5), c = 9.671(2), beta = 117.32(3) degrees, Z = 4; 4, space group P2(1)/c, a = 9.761(2), b = 28.668(5), c = 9.941(2), beta = 96.07(3) degrees, Z = 4.

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