L. Ouahab

Hepta/octa cyanomolybdates with Fe2+: influence of the valence state of Mo on the magnetic behavior

Two FeII-based molybdenum polycyanides, Fe2[MoIII(CN)7]·8H2O and [Fe2(H2O)4][MoIV(CN)8]·4H2O, have been synthesized. The compound [Fe2(H2O)4][MoIV(CN)8]·4H2O crystallizes in the tetragonal system, space group I422. There are two molybdenum sites in a distorted square antiprism arrangement, each site being surrounded by eight CN–Fe linkages. The distorted octahedral iron site is formed by four NC–Mo linkages and two water molecules in apical positions. The structure is three-dimensional and highly symmetrical. The magnetic characteristics of these two compounds were compared. Fe2[MoIII(CN)7]·8H2O orders below 65 K as a ferrimagnet, but [Fe2(H2O)4][MoIV(CN)8]·4H2O shows no evidence of long-range magnetic order, obviously due to the contribution of the diamagnetic MoIV which suppresses the propagation of magnetic interaction between adjacent iron(II) ions through CN bridges. The results are discussed in the light of the single-crystal structural features of [Fe2(H2O)4][MoIV(CN)8]·4H2O.

Phase transitions in [κ-(ET4N)ET4M(CN)6, 3 H2O; M = FeIII, CoIII, CrIII]

Abstract We report the preparation, structural and physical investigations of BEDT-TTF (ET) salts formulated κ-[Et 4 N](ET) 4 M(CN) 6 , 3 H 2 O (M = Fe III , Co III , Cr III ). These κ-phases show two phase transitions at 240 K and 150 K. The first structural transition, at 240 K, is followed by a redistribution of the charges on the ET molecules and the magnetic and electrical properties are explained on the basis of this phenomenon.

Physical properties of BEDT-TTF radical ion salts with Keggin type polyoxometalates

Abstract ESR measurements of the series of radical salts formed by ET and inorganic polyoxometalates are presented and compared with the susceptibility data. Both experiments show that the organic radicals are antiferromagnetically coupled whereas no sizable magnetic coupling is found between the two magnetic sublattices.

Preparation and properties of tetrathia- and tetramethyltetraselena-fulvalene salts of [M6O19]2–(M = Mo or W)

The preparation, X-ray crystal structures, conductivity and optical properties of the salts, [ttf]3[W6O19]1, [ttf]3[Mo6O19]2(ttf = tetrathiafulvalene) and [tmtsf]3[W6O19]·2dmf 3(tmtsf = tetramethyltetraselenafulvalene) are reported. Crystal data: 1, triclinic, space group P, a= 9.965(3), b= 10.503(3), c= 10.634(3)A, α= 71.93(2), β= 78.63(2), γ= 63.38(3), Z= 1, R= 0.020; 2, triclinic, space group P, a= 9.942(3), b= 10.417(3), c= 10.601(3), α= 72.33(2), β= 78.77(2), γ= 63.52(3)°, Z= 1, R= 0.030; 3, monoclinic, space group P21/c, a= 11.589(4), b= 19.385(5), c= 13.681(3), β= 99.53(2), Z= 2 and R= 0.049. In all the salts the organic molecules form trimerized stacks. A classical ring-over-double bond overlap is observed in 3, in contrast with 1 and 2 which present an unusual intra-trimer criss-cross overlap. In compound 3 the intra-trimer Se ⋯ Se (3.73–3.81 A) contacts are shorter than those observed in [tmtsf]2X (X = PF6 or BF4) series. The inter-trimer Se ⋯ Se contacts (3.94–4.12 A) are in the range of the van der Waals separation (4 A). Short O ⋯ Se (3.17–3.30 A) contacts are observed. Both electrical and optical measurements and also electronic band-structure calculations reveal that the three salts are semiconductors.

Molecular Materials Containing Conducting and Magnetic Sublattices: Phase Transitions in [k-(Et4N)(BEDT-TTF)4M(CN)6, 3 H2O; M = FeIII, CoIII, CrIII]

Abstract We report the preparation, structural and physical investigations of BEDT-TTF (ET) salts formulated β-ET5M(CN)6, 10 H2O with M = FeIII and CoIII and k-[Et4N] (ET)4M(CN)6. 3 H2O with M = FeIII, CoIII and CrIII. The k-phase salts show two phase transitions at 240 K and 150 K, respectively. The first structural transition, at 240 K, is followed by a redistribution of the charges on the ET molecules and the magnetic and electrical properties are explained on the basis of this phenomenon. A facile and convenient route for the preparation of the (R4N)3M(CN)6 [R= C2H5 and C4H9) salts is also presented.

Synthesis, structure and hydrogenation catalytic activity of [Ru3(μ3,η2-ampy)(μ,η1:η2-PhCCHPh)(CO)6(PPh3) (Hampy = 2-amino-6-methylpyridine)

Abstract The compound [RU 3 (μ 3 ,η 2 - -ampy)(μ 3 η 1 :η 2 -PhCCHPh)(CO) 6 (PPh 3 ) 2 ] ( 1 ) (ampy = 2-amino-6-methylpyridinate) has been prepared by reaction of [RU 3 (η-H)(μ 3 ,η 2 - ampy) (μ,η 1 :η 2 -PhCCHPh)(CO) 7 (PPh 3 )] with triphenylphosphine at room temperature. However, the reaction of [RU 3 (μ-H)(μ 3 , η 2 -ampy)(CO) 7 (PPh 3 ) 2 ] with diphenylacetylene requires a higher temperature (110°C) and does not give complex 1 but the phenyl derivative [RU 3 (μ 3 ,η 2 -ampy)(μ,η 1 :η 2 -PhCCHPh)(μ,-PPh 2 )(Ph)(CO) 5 (PPh 3 )] ( 2 ). The thermolysis of complex 1 (110°C) also gives complex 2 quantitatively. Both 1 and 2 have been characterized by0 X-ray diffraction methods. Complex 1 is a catalyst precursor for the homogeneous hydrogenation of diphenylacetylene to a mixture of cis - and trans -stilbene under mild conditions (80°C, 1 atm. of H 2 ), although progressive deactivation of the catalytic species is observed. The dihydride [RU 3 (μ-H) 2 (μ 3 ,η 2 -ampy)(μ,η 1 :η 2 - PhCCHPh)(CO) 5 (PPh 3 ) 2 ] ( 3 ), which has been characterized spectroscopically, is an intermediate in the catalytic hydrogenation reaction.

An organic-inorganic salt containing mixed-valence TTF chains and the molecular metal oxide cluster [Mo8O26]−4. Preliminary spectroscopic, conducting and magnetic properties of the compound (TTF)7Mo8O26

Abstract A new organic-inorganic salt formed by mixed-valence TTF chains and [Mo 8 O 26 ] −4 is obtained by electrochemical oxidation of the donor in acetonitrile solution containing the polyanion. A unusual zigzag stacking of the donor molecules along the b-axis of the triclinic cell is observed, with close intrachain and interchain contacts through the sulpur atoms (the shortest S-S distances are about 3.5 A). A semiconducting behavior has been observed with a conductivity σ ≈ 10 −3 S.cm −1 at room temperature. The magnetic properties indicate that the compound is non magnetic.

Weak ferromagnetism of (BDH-TTP)[M(isoq)2(NCS)4] (M = Cr

Radical-ion salts of a TTP-type donor BDH-TTP and paramagnetic anions [M(isou) 2 (NCS) 4 ] (M = Cr, Fe) show bulk weak ferromagnetism at 7.6 K. The donor cation radicals (S=1/2) and anions (S=3/2 (Cr), 5/2 (Fe)) form ferrimagnetic chains spanned by close intermolecular S...S contacts, which are then antiferromagnetically coupled with each other through;h the π-π overlap of the ligands. The non-parallel alignment of the molecular axes of adjacent anions leads to the canted spin structure.

Hybrid Molecular Systems Containing Tetrathiafulvalene and Iron‐Alkynyl Electrophores: Five‐Component Functional Molecules Obtained from CH Bond Activation

Treatment of [Cp*(dppe)Fe-C≡C-TTFMe3] (1) with Ag[PF6] (3 equiv) in DMF provides the binuclear complex [Cp*(dppe)Fe=C=C=TTFMe2 =CH-CH=TTFMe2 =C=C=Fe(dppe)Cp*][PF6]2 (2[PF6 ]2) isolated as a deep-blue powder in 69 % yield. EPR monitoring of the reaction and comparison of the experimental and calculated EPR spectra allowed the identification of the radical salt [Cp*(dppe)Fe=C=C=TTFMe2 =CH][PF6]2 ([1-CH][PF6]) an intermediate of the reaction, which results from the activation of the methyl group attached in vicinal position with respect to the alkynyl-iron on the TTF ligand by the triple oxidation of 1 leading to its deprotonation by the solvent. The dimerization of [1-CH][PF6] through carbon-carbon bond formation provides 2[PF6]2. The cyclic voltammetry (CV) experiments show that 2[PF6]2 is subject to two sequential well-reversible one-electron reductions yielding the complexes 2[PF6] and 2. The CV also shows that further oxidation of 2[PF6]2 generates 2[PF6]n (n=3-6) at the electrode. Treatment of 2[PF6]2 with KOtBu provides 2[PF6] and 2 as stable powders. The salts 2[PF6] and 2[PF6]2 were characterized by XRD. The electronic structures of 2(n+) (n=0-2) were computed. The new complexes were also characterized by NMR, IR, Mössbauer, EPR, UV/Vis and NIR spectroscopies. The data show that the three complexes 2[PF6]n are iron(II) derivatives in the ground state. In the solid state, the dication 2(2+) is diamagnetic and has a bis(allenylidene-iron) structure with one positive charge on each iron building block. In solution, as a result of the thermal motion of the metal-carbon backbone, the triplet excited state becomes thermally accessible and equilibrium takes place between singlet and triplet states. In 2[PF6], the charge and the spin are both symmetrically distributed on the carbon bridge and only moderately on the iron and TTFMe2 electroactive centers.

Ferromagnetic Interactions in Supramolecular Assemblies Constructed from Nitronyl Nitroxide Radical Cations and Large Inorganic Polyoxometalates

Abstract The synthesis, crystal structures and magnetic properties of two nitronyl nitroxide radical salts of polyoxometalates are reported. The para-radical 2-(4-N-methylpyridinium-4,4,5,5-tetramethylimidazoline)-1-oxyl-3-oxide was associated to Lindquist polyoxometalates [M6O19]2- with M=Mo, W to give (para-rad)2-Mo6O19 (1) and (para-rad)2-W6O19 (2) which are isostructural. The magnetic measurements show ferromagnetic interactions for (1) and (2).