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The Mössbauer spectra of the two crystallographic forms α- and β-(NH4)2FeF5 have been studied in the temperature range 4.2-300 K. The α-form presents typical one-dimensional behavior showing a transition to magnetic ordering at Tc = (7.5±0.5) K. The spectra of the β-form indicates the presence at low temperature of two different iron sites, while the room temperature crystal structure shows only one site for the iron ions. Differential scanning calorimetry measurements evidence the presence of a reversible structural phase transition at Ts = (168.0±1) K on heating and Ts = (187.0±3) K on cooling. This form also exhibits a magnetic ordering phase transition at Tc = (13±1) K., The work in Zaragoza has been supported by grant MAT88-0174, from the Comision Interministerial de Ciencia y Tecnologia. M.C.M. is grateful for the receipt of a NATO postdoctoral fellowship. The cooperation has been partially supported by Spanish-French Integrated Action 151/90.

6 pages, 5 figures, 1 table., Compositions of the Cd(1-x)Mn(x)In2S4 system (0.5 x 1.0) were synthesized by the melt and annealing technique and grown by the chemical vapor transport method. The magnetic cation distributions have been estimated by X-ray powder diffraction structure refinements using the Rietveld method. These alloys form a solid solution in all the range of compositions and crystallize with cubic symmetry in the space group Fd 3m. All phases show a spinel structure with a random arrangement of cations. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim), This work was supported by CDCHT-ULA(C-1395-06-05-B), FONACIT-Venezuela (Grant LAB-97000821) and Comisión Interministerial de Ciencia y Tecnología-Spain (CICYT-AT2004-03395-C0201).

We report on the magnetic properties of the complex bimetallic compound [Cr(H2O)(NH3)5][FeCl6] studied by ac magnetic susceptibility and magnetization techniques in the range 1.5-30 K and 0-40 kOe. The crystal structure contains discrete [Cr(H2O)(NH3)5]3+ and [FeCl6]3- ions, held together by ionic forces and by a network of hydrogen bonds. At temperatures below (2.32±0.01) K the compound seems to behave as a noncollinear ferrimagnet. In addition, the experimental H-T magnetic phase diagram has been derived., The research has been supported by Grants CAICYT 3380/83 and CICYT MAT 88-0174.

Magnetization and frequency dependence a.c. magnetic susceptibility measurements of the metal-organic polymers of general formula {[M(C13H17N3)2]SO4 6H2O}n, where M = Fe(II) or Co(II), are indicative of superparamagnetic behavior as a consequence of the existence of strong ferromagnetic interactions in the materials. Scanning electron microscopy and X-ray dispersive spectrometry have been used to study the homogeneity in the composition of the iron polymer.

The compound [Cr(en)3][ZnCl4]Cl has been synthesized by reaction of CrCl3·6H2O, Zn and [Cr(en)3]2(SO4)3 in HCl. Its molecular and crystalline structure was determined by X-ray diffraction methods, being monoclinic, P21/c, a=21.215(3), b=12.532(2), c=13.707(2) Å, β=95.21°, V= 3629(2) Å3, Dx=1.738g cm−3, MW=474.9, Z= 8, F(000)=1928, λ(Mo Kα)=0.71069 Å, μ(Mo Kα)= 27.04 cm−1, 288 K. No significant exchange interactions between Cr(III) cations in the crystalline lattice were found. Curie-Weiss behavior was found in the three directions tested (g1=2.06±0.02,g2= 2.08±0.02,g3=2.09±0.01), T=1.2-1.4 K., The work in Barcelona has been supported by ‘Comisión Asesora de Investigación Cientifica y Técnica, (C.A.T.C.Y.T.)’ Spanish Government, Grant no. 360/81. The work in Chicago was supported by the Solid State Chemistry Program of the Division oMaterials Research of the National Science Foundation under Grant DMR 8515224. This research was also supported by the U.S.-Spain Joint Committee for Scientific and Technological Cooperation. M.C.M. also acknowledges a Doctoral Fellowship from the Spanish M.E.C.

The compound [Cr(en)3][ZnCl4]Cl has been synthesized by reaction of CrCl3·6H2O, Zn and [Cr(en)3]2(SO4)3 in HCl. Its molecular and crystalline structure was determined by X-ray diffraction methods, being monoclinic, P21/c, a=21.215(3), b=12.532(2), c=13.707(2) A, β=95.21°, V= 3629(2) A3, Dx=1.738g cm−3, MW=474.9, Z= 8, F(000)=1928, λ(Mo Kα)=0.71069 A, μ(Mo Kα)= 27.04 cm−1, 288 K. No significant exchange interactions between Cr(III) cations in the crystalline lattice were found. Curie-Weiss behavior was found in the three directions tested (g1=2.06±0.02,g2= 2.08±0.02,g3=2.09±0.01), T=1.2-1.4 K.

Les deux composes du titre cristallisent dans le systeme orthorhombique avec le groupe d'espace Pnma. Affinement de la structure jusqu'a 0,020 pour les deux composes. Les anions sont des octaedres deformes