[en] We present an x-ray diffuse scattering study of the anion ordering (AO) transition in the (TMTSF)₂(ReO₄)_1-x(ClO₄)_x solid solution of quasi-one-dimensional organic conductors and superconductors. As (TMTSF)₂ReO₄ and (TMTSF)₂ClO₄ present AO instabilities at different critical wave vectors [q₁=( (1) /(2) , (1) /(2) , (1) /(2) ) and q₂=(0, (1) /(2) ,0), respectively] this solid solution allows for the study of the influence of competing interactions on a structural transition. The order parameter of this transition can be characterized by an Ising variable representing the two possible orientations of the ReO₄^- or ClO₄^- anion in cavities delimited by organic TMTSF molecules. Furthermore, the random substitution of the anions shows that these interactions are randomly distributed. The phase diagram of the AO transition has been determined as a function of x. At low temperatures (T) a q₁ long-range order (LRO) occurs for x≤0.5 and a q₂ LRO occurs for 1≤x≤0.97, while a short-range order (SRO) appears in the intermediate concentration range. For 0.7< x<0.94 one observes coexistence of q₁ and q₂ SRO. The basic features of the (T,x) phase diagram can be accounted for by a mean-field treatment of the Ising model with random interactions. This model, however, fails to reproduce all the details of the phase diagram, such as the x dependence of the critical wave vector. Finally, we discuss the implications of this structural phase diagram on the electronic properties of the solid solution. copyright 1997 The American Physical Society

[en] The reaction in gel of Gd(III) ions with TMA^3-, where TMA^3- stands for [C₆H₃(COO)₃]^3-, has afforded single crystals of a bidimensional molecular compound formulated as Gd[TMA(H₂O)₃].1.5H₂O whose crystal structure is reported here: C2/c, a=20.454(2) A, b=9.973(1) A, c=15.251(2) A, β=125.68(1) and Z=8. The structure consists of parallel double-sheet networks based on honeycomb-like motifs based on Gd(III) ions and TMA^3- groups. This compound exhibits a paramagnetic behaviour in the whole temperature range (2-300K). (orig.)

[en] A straightforward preparation in water of the title compound is reported. The determination of its crystal structure demonstrates the presence of discrete octahedral molecular anions ZrF₆^2-. In addition, this solvate is shown to be soluble and subsequently dehydrated in a variety of polar nonaqueous solvents

[en] Structural, electrical, and magnetic studies of [(TMTSF)_1-x(TMTTF)_x]₂ReO₄ alloys are reported. They exhibit around x∼0.5 an enhanced charge localization and a strong decrease of the (1/2,1/2,1/2) anion-ordering (AO) transition temperature. The localization enhancement is attributed to a 4k_F order of charge on the sites due to the alternate order of TMTSF and TMTTF molecules. This heteropolar charge distribution is suggested to weaken the 2k_F bond response and thus to depress the AO transition. These properties contrast with those exhibited by the hybrid salt (TMDTDSF)₂ReO₄