Fatima Setifi

Magnetic bistability and thermochromism in a molecular Cu(II) chain.

An original magnetic bistability and a thermochromic transition are observed in a new Cu(II) molecular chain. Thermal structural studies reveal changes in the Cu(II) coordination sphere, driven by a more pronounced Jahn-Teller effect at low temperature. These distortions provoke a gradual color change. The structural study at 10 K shows a dimerization of the molecular chain, in agreement with the abrupt magnetic transition observed at 30 K.

Preparation, X-ray crystal structures and properties of α-(BEDT-TTF)2[FeIII(phen)(NCS)4]·2CH2Cl2 and (BEDT-TTF)[CrIII(isoq)2(NCS)4] (phen = 1,10-phenanthroline; isoq = isoquinoline)

This paper reports the preparation, X-ray crystal structure, conducting and magnetic properties of α-(BEDT-TTF)2[FeIII(phen)(NCS)4] (1) [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene, phen = 1,10-phenanthroline] together with the crystal structure of (BEDT-TTF)[CrIII(isoq)2(NCS)4] (2) (isoq = isoquinoline) for which the physical properties have been reported previously. Compound 1 crystallizes in the triclinic space group P (no. 2), a = 12.1528(1), b = 16.8269(3), c = 27.0703(4) A, α = 95.726(1), β = 95.834(1), γ = 108.080(1)°, Z = 4, R = 0.0610 for 9764 reflections with I > 2σ(I); 2 crystallizes in the monoclinic space group P21/c (no. 14), a =10.623(5), b = 14.656(8), c = 12.701(7) A, β = 100.19(2)°, Z = 2, R = 0.0737 for 2747 reflections with I > 2σ(I). The magnetic and transport properties have shown that compound 1 is a paramagnetic semiconductor with σ300 K = 2.2 × 10−2 Ω−1 cm−1.

Tris(1,10-phenanthroline-κ2N,N′)iron(II) bis­(1,1,3,3-tetra­cyano-2-eth­oxy­propenide) hemihydrate

In the title hydrated molecular salt, [Fe(C12H8N2)3](C9H5N4O)2·0.5H2O, the water molecule site is half-occupied. The Fe—N bond lengths within the octahedral tris-chelate [Fe(phen)3]2+ ion (phen is 1,10-phenantroline) are indicative of a low-spin d 6 electronic configuration for the metal ion. The C—N, C—C and C—O bond lengths in the polynitrile anions indicate extensive electronic delocalization. In the crystal, the components are linked through O—H⋯N hydrogen bonds, forming [100] chains, as well as through Coulombic interactions.

Spin Crossover Iron(II) Coordination Polymer Chains: Syntheses, Structures, and Magnetic Characterizations of [Fe(aqin)2(μ2-M(CN)4)] (M = Ni(II), Pt(II), aqin = Quinolin-8-amine)

New Fe(II) coordination polymeric neutral chains of formula [Fe(aqin)2(μ2-M(CN)4)] (M = Ni(II) (1) and Pt(II) (2)) (aqin = Quinolin-8-amine) have been synthesized and characterized by infrared spectroscopy, X-ray diffraction, and magnetic measurements. The crystal structure determinations of 1-2 reveal in both cases a one-dimensional structure in which the planar [M(CN)4](2-) (M = Ni(II) (1) and Pt(II) (2)) anion acts as a μ2-bridging ligand, and the two aqin molecules as chelating coligands. Examination of the intermolecular contacts in the two compounds reveals that the main contacts are ascribed to hydrogen bonding interactions involving the amine groups of the aqin chelating ligands and the nitrogen atoms of the two non bridging CN groups of the [M(CN)4](2-) (M = Ni(II) (1) and Pt(II) (2)) anion. The average values of the six Fe-N distances observed respectively at room temperature (293 K) and low temperature (120 K), that is, 2.142(3) and 2.035(2) Å for 1, and 2.178(3) and 1.990(2) Å for 2, and the thermal variation of the cell parameters (performed on 2) are indicative of the presence of an abrupt HS-LS spin crossover (SCO) transition in both compounds. The thermal dependence of the product of the molar magnetic susceptibility times the temperature (χmT), in cooling and warming modes, confirms the SCO behavior at about 145 and 133 K in 1 and 2, respectively, and reveals the presence of a small thermal hysteresis of about 2 K for each compound.

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.

Bis(2,2′-bi-1H-imidazole)­copper(II) bis­(1,1,3,3-tetra­cyano-2-eth­oxy­propenide)

In the title compound, [Cu(C6H6N4)2](C9H5N4O)2, the Cu2+ ion (site symmetry ) is coordinated by two N,N′-bidentate 2,2′-biimidazole (H2biim) ligands, generating a square-planar CuN4 geometry. The dihedral angle between the aromatic rings in the ligand is 0.70 (9)°. In the polynitrile 1,1,3,3-tetracyano-2-ethoxypropenide (tcnoet) anion, the C—N, C—C and C—O bond lengths indicate extensive electronic delocalization. An alternative description for the metal-ion geometry is an extremely distorted CuN6 octahedron, with two N-bonded tcnoet anions completing the coordination. In the crystal, the components are linked by N—H⋯N and C—H⋯N interactions.

Tris(2,2'-bipyridine)iron(II) bis(1,1,3,3-tetracyano-2-ethoxypropenide) dihydrate : chiral hydrogen-bonded frameworks interpenetrate in three dimensions

In the title compound, [Fe(C10H8N2)3](C9H5N4O)2·2H2O, the chiral cations lie across twofold rotation axes in the space group C2/c. The anions and the water molecules are linked by two independent O-H···N hydrogen bonds to form C2(2)(8) chains, and these chains are linked by the cations via C-H···N and C-H···O hydrogen bonds to form two interpenetrating three-dimensional frameworks, each of which contains only one enantiomeric form of the chiral cation.

π–d Interaction-based molecular magnets

Abstract The crystal structures and physical properties of molecular magnets developed in our group are reviewed. (1) (DMET) 2 FeBr 4 and its analogues are composed of alternating stacks of quasi-one-dimensional donor sheets and square lattice magnetic anion sheets. These salts undergo an SDW transition of the donor layer and an antiferromagnetic transition of Fe 3+ spins on the anion layer. The one-to-one correspondence of the anomalies appearing on the magnetization curves and the magnetoresistance supports the presence of the π–d interaction. On applying pressure, a large negative magnetoresistance is observed for the all-sulfur compound (EDTDM) 2 FeBr 4 in the marginal region of the SDW and metallic ground states. (2) (BDH-TTP)[M(isoq) 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 with close intermolecular S⋯S contacts, which are then antiferromagnetically coupled through the π – π overlap of the ligands and inter-chain S⋯S contacts of the donors. The non-collinear alignment of the molecular axes of adjacent anions is responsible for the canted spin structure.

Crystal structures of 2,2′-bipyridin-1-ium 1,1,3,3-tetracyano-2-ethoxyprop-2-en-1-ide and bis(2,2′-bipyridin-1-ium) 1,1,3,3-tetracyano-2-(dicyanomethylene)propane-1,3-diide

In each of the title compounds, the anion shows evidence of extensive electronic delocalization. A combination of N—H⋯N and X—H⋯N hydrogen bonds links the ions in (I) into a ribbon of alternating centrosymmetric (18) and (26) rings, and those in (II) into simple (7) chains of alternating cations and anion with further cations pendent from the chain.

Crystal structure of tetra­aqua­(5,5′-dimethyl-2,2′-bipyridyl-κ2N,N′)iron(II) sulfate

In the crystal structure of the title compound, [Fe(dmbpy)(H2O)4][SO4], the charged components form an extensive hydrogen-bonding network. Eight O—H⋯O hydrogen bonds [d(O⋯H) < 2.00 Å], form a two-dimensional network parallel to the ab plane.