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μ-Benzene-1,2,4,5-tetracarboxylato-κ2O1:O4)bis-[aqua-bis-2-(aminomethyl) pyridine-κ2N,N’) nickel (II)] decahydrate, [Ni2(amp)4(btc)(H2O)2]10H2O has been synthesized and its crystal structure determined by X-ray diffraction. The complex crystallizes in the Monoclinic space group P21/n with cell dimensions a= 11.0102 (10) Å, b= 21.5416 (19) Å, c= 11.0445 (10) Å and β= 118.753 (1)°, and two formula units per cell (Z= 2, Z’= 0.5). The structure consists of centrosymmetric dimeric units in which the benzene tetracarboxylate anions (btc) bridge the symmetry-related nickel (II) cations, two bidentate chelating molecules of 2-(aminomethyl) pyridine and a terminal aqua ligand completing the six-fold coordination at each metal. These dimers link to each other via H-bonding to form chains parallel to [100], while the water solvates form a strongly bound 2D network parallel to (100), made up by small (R44(8)) and large (R2020(40)) rings, the latter ones “pierced” by the chains of dimmers, with a profuse H-bonding interconnection between both substructures. Magnetic susceptibility measurements as a function of temperature disclose weak interdimeric exchange interactions. Fitting of these data to a dimeric model yields J= −3.5 cm-1 and g= 2.13.

μ-Benzene-1,2,4,5-tetracarboxylato-κ2O1:O4)bis-[aqua-bis-2-(aminomethyl) pyridine-κ2N,N’) nickel (II)] decahydrate, [Ni2(amp)4(btc)(H2O)2]10H2O has been synthesized and its crystal structure determined by X-ray diffraction. The complex crystallizes in the Monoclinic space group P21/n with cell dimensions a= 11.0102 (10) Å, b= 21.5416 (19) Å, c= 11.0445 (10) Å and β= 118.753 (1)°, and two formula units per cell (Z= 2, Z’= 0.5). The structure consists of centrosymmetric dimeric units in which the benzene tetracarboxylate anions (btc) bridge the symmetry-related nickel (II) cations, two bidentate chelating molecules of 2-(aminomethyl) pyridine and a terminal aqua ligand completing the six-fold coordination at each metal. These dimers link to each other via H-bonding to form chains parallel to [100], while the water solvates form a strongly bound 2D network parallel to (100), made up by small (R44(8)) and large (R2020(40)) rings, the latter ones “pierced” by the chains of dimmers, with a profuse H-bonding interconnection between both substructures. Magnetic susceptibility measurements as a function of temperature disclose weak interdimeric exchange interactions. Fitting of these data to a dimeric model yields J= −3.5 cm-1 and g= 2.13.

International audience; mu-Benzene-1,2,4,5-tetracarboxylato-kappa O-2(1)O-4)bis-[aqua-bis-2-(aminomethyl) pyridine-kappa N-2,N') nickel (II)] decahydrate, [Ni-2(amp)(4)(btc)(H2O)(2)]center dot 10H(2)O has been synthesized and its crystal structure determined by X-ray diffraction. The complex crystallizes in the Monoclinic space group P2(1)/n with cell dimensions a= 11.0102 (10) angstrom, b = 21.5416 (19) angstrom, c = 11.0445 (10) angstrom and beta = 118.753 (1)degrees, and two formula units per cell (Z = 2, Z' = 0.5). The structure consists of centrosymmetric dimeric units in which the benzene tetracarboxylate anions (btc) bridge the symmetry-related nickel (II) cations, two bidentate chelating molecules of 2-(aminomethyl) pyridine and a terminal aqua ligand completing the six-fold coordination at each metal. These dimers link to each other via H-bonding to form chains parallel to [100], while the water solvates form a strongly bound 2D network parallel to (100), made up by small (R-4(4)(8)) and large (R-20(20)(40)) rings, the latter ones "pierced" by the chains of dimmers, with a profuse H-bonding interconnection between both substructures. Magnetic susceptibility measurements as a function of temperature disclose weak interdimeric exchange interactions. Fitting of these data to a dimeric model yields J=-3.5 cm(-1) and g=2.13.

The crystalline structure of spinels is extremely flexible due to the presence of several sublattices in which the cations can be distributed and localized in different crystallographic sites depending on their sizes, oxidation states or coordination numbers. Cationic substitution and ions-extraction are appropriate tools to change the oxidation state inside the spinel structure, thus substantially modifying the magnetic properties. The spinel sulfide CuCr2S4 is a metallic ferromagnet with T C = 377 K, where Cr is mixed-valence Cr3+/Cr4+, while CuTi2S4 is a Pauli paramagnet, with Ti in a mixed-valence state (singlet ground state for Ti3+; nonmagnetic, S = 0, state for Ti4+). The copper ion Cu+ is in a closed-shell configuration. The mixed spinel CuCr2-xTi xS4 gives the possibility to change the oxidation state of Cr ions when titanium ions are introduced. Another way to control the oxidation state of the ions is by copper extraction from the lattice, thus producing a change in the magnetic behavior of the material. We report the synthesis, crystallographic and magnetic properties of the solid solution CuCr2-xTi xS4 and its deficient-spinel structure obtained by copper extraction. Powder samples of CuCr2-xTi xS4 were prepared in quartz ampoules at 900 °C. Deficient spinels Cu1-y□yCr2-xTi xS4 were prepared by mild treatment with oxidizing agents such as iodine in acetonitrile at 50 °C.

The crystalline structure of spinels is extremely flexible due to the presence of several sublattices in which the cations can be distributed and localized in different crystallographic sites depending on their sizes, oxidation states or coordination numbers. Cationic substitution and ions-extraction are appropriate tools to change the oxidation state inside the spinel structure, thus substantially modifying the magnetic properties. The spinel sulfide CuCr2S4 is a metallic ferromagnet with T C = 377 K, where Cr is mixed-valence Cr3+/Cr4+, while CuTi2S4 is a Pauli paramagnet, with Ti in a mixed-valence state (singlet ground state for Ti3+; nonmagnetic, S = 0, state for Ti4+). The copper ion Cu+ is in a closed-shell configuration. The mixed spinel CuCr2-xTi xS4 gives the possibility to change the oxidation state of Cr ions when titanium ions are introduced. Another way to control the oxidation state of the ions is by copper extraction from the lattice, thus producing a change in the magnetic behavior of the material. We report the synthesis, crystallographic and magnetic properties of the solid solution CuCr2-xTi xS4 and its deficient-spinel structure obtained by copper extraction. Powder samples of CuCr2-xTi xS4 were prepared in quartz ampoules at 900 °C. Deficient spinels Cu1-y□yCr2-xTi xS4 were prepared by mild treatment with oxidizing agents such as iodine in acetonitrile at 50 °C.

[EN] The phase transition to perovskite-type structure, that occurs in some hexagonal manganites when foreign cations are incorporated into solid solution, has been studied. Several solid solution series belonging to the Y(Mn, Ni)O3, (Er, Ca)MnO3, (Y, Ca)MnO3, systems have been prepared by solid state reaction between the corresponding oxides. The crystalline structure of the different solid solutions has been established. The behaviour of the (Gd, Ca)MnO3 system has been taken as a reference. The obtained results are discussed as a function of the tolerance factor and the Mn3+/Mn4+ ratio. The transition to perovskite structure is governed by this Mn3+/Mn4+ ratio rather than the increase of the tolerance factor. [ES] Se ha estudiado la transición de fase a estructura de tipo perovskita que ocurre en algunas manganitas hexagonales cuando se incorporan iones aliovalentes formando soluciones sólidas. Se han preparado soluciones sólidas pertenecientes a los sistemas Y(Mn, Ni)O3, (Er, Ca)MnO3, (Y, Ca)MnO3 por reacción en estado sólido entre los óxidos. Se ha determinado la estructura cristalina de los diferentes compuestos, y los resultados se comparan con los observados en los correspondientes al sistema (Gd, Ca)MnO3. Los resultados se discuten en función del factor de tolerancia y de la razón Mn3+/Mn4+. La transición es gobernada por dicha razón más bien que por la variación del factor de tolerancia. This work was supported under contract CICYT-MAT-97- 0679-C02-01.

Las propiedades estructurales de las soluciones sólidas RE(Me,Mn)O3, RE=Gd,Er, Me=Ni,Co, han sido estudiadas por difracción de rayos X, (DRX) y medidas eléctricas. Las fases se sintetizaron por reacción en estado sólido entre los óxidos componentes. La incorporación de los cationes Ni2+ y Co2+,3+ en la red en lugar de Mn lleva a cambios en los parámetros de red y en la simetría de la perovskita, GdMnO3 o del compuesto hexagonal ErMnO3 respectivamente. Las transiciones de fase dependen de la cantidad de Mn3+ sustituido, y por tanto de la debilitación del efecto co-operativo Jahn-Teller. Las soluciones sólidas basadas en GdMnO3 cambian de perovskita tipo O’ a perovskita tipo O. Esta transición ocurre para una menor cantidad de Ni que para Co como sustituyentes. Las soluciones basadas en ErMnO3 muestran un comportamiento algo diferente: la incorporación induce cambios desde la estructura hexagonal a una estructura tipo perovskita en la forma O, para cantidades de ~20 at% Ni y para ~30 at% Co. La influencia del factor estérico en las transiciones observadas parece jugar un papel secundario frente a la desaparición progresiva de los cationes Jahn-Teller Mn3+

[EN] Magnetic properties of the Er(Co,Mn)O3 solid solution result from a subtle interplay of different interactions between erbium moments and several other magnetic entities present in this system: Mn3+, Mn4+, Co2+, Co3+, as well as double-exchange interactions among them. The special case of the 0.5:0.5 = Co:Mn substitution is particularly important since ferromagnetic domains may reorientate both under low and high external magnetic fields. Magnetic dilution of the erbium sublattice by non-magnetic yttrium (same valence and size) allows separating out the antiferromagnetic 4f-3d interactions leaving just the ferromagnetic Co2+-Mn4+ transition metal sublattice. Magnetic properties of the ErxY1-xCo0.50Mn0.50O3 (0.0 ≤ x ≤ 1.0) solid solution are presented, going from ferromagnetism (x = 0; YCo0.5Mn0.5O3) to ferrimagnetism (x = 1; ErCo0.5Mn0.5O3). Antiferromagnetic interactions get stronger while the Co/Mn ferromagnetic domains become harder to rotate when the rare-earth sublattice is progressively filled with erbium ions of large magnetic moments. A linear dependence with x(Er) is observed for the critical field Hcrit related to the reorientation of domains, going from 1.3 T up to 3.5 T, for x = 0 and 1, respectively. At the same time, the compensation temperature Tcomp increases and the spontaneous magnetization Mrem decreases with increasing content of erbium. [ES] Las propiedades magnéticas de las soluciones sólidas ErxY1-xCo0.50Mn0.50O3 (0.0 ≤ x ≤ 1.0) son consecuencia de una sutil interrelación de las diferentes interacciones entre los momentos magnéticos del Er3+ y de otras entidades magnéticas presentes en el sistema: Mn3+, Mn4+, Co2+, Co3+, así como las interacciones de doble canje entre ellas. El caso especial de la sustitución 0.5:0.5 = Co:Mn es particularmente importante puesto que los dominios ferromagnéticos pueden reorientarse bien con campos externos bajos como con altos. La dilución magnética de la subred de Er3+ por el ión no-magnético Y3+ (del mismo tamaño y valencia) permite separar las interacciones antiferromagnéticas 4f-3d dejando solamente las interacciones ferromagnéticas Co2+-Mn4+ de la subred de los metales de transición. Las propiedades magnéticas de las soluciones sólidas ErxY1-xCo0.50Mn0.50O3 (0.0 ≤ x ≤ 1.0) se presentan como variando desde ferromagnetismo (x = 0; YCo0.5Mn0.5O3) a ferrimagnetismo (x = 1; ErCo0.5Mn0.5O3). Las interacciones antiferromagnéticas se hacen más fuertes mientras que los dominios ferromagnéticos se hacen más difíciles de rotar cuando la subred de la tierra rara se va llenando progresivamente con iones Er3+, de momento magnético alto. Se observa una dependencia lineal con x(Er) del campo crítico Hcrit relacionado con la reorientación de dominios, variando desde 1.3 T hasta 3.5 T, para x = 0 y 1, respectivamente. Al mismo tiempo, la temperatura de compensación, Tcomp aumenta y la magnetización espontánea, Mrem disminuye con el contenido creciente de Er3+. Authors acknowledge the bilateral exchange programs France-Spain CNRS-CSIC, project n° 18873, and France-Brazil CAPES-COFECUB, project 416/03.