Smail Triki

The Key Role of the Intermolecular π−π Interactions in the Presence of Spin Crossover in Neutral [Fe(abpt)2A2] Complexes (A = Terminal Monoanion N Ligand)

New iron(II) complexes of formulas [Fe(abpt) 2(tcm) 2] ( 1), [Fe(abpt) 2(tcnome) 2] ( 2), and [Fe(abpt) 2(tcnoet) 2] ( 3) (abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole, tcm (-) = [C(CN) 3] (-) = tricyanomethanide anion; tcnome (-) = [(NC) 2CC(OCH 3)C(CN) 2] (-) = 1,1,3,3-tetracyano-2-methoxypropenide anion; tcnoet (-) = [(NC) 2CC(OC 2H 5)C(CN) 2] (-) = 1,1,3,3-tetracyano-2-ethoxypropenide anion) have been synthesized and characterized by infrared spectroscopy, magnetic properties and by variable-temperature single-crystal X-ray diffraction. The crystal structure determinations of 1 and 2 reveal in both cases centrosymmetric discrete iron(II) monomeric structures in which two abpt chelating ligands stand in the equatorial plane and two terminal polynitrile ligands complete the distorted octahedral environment in trans positions. For 3, the crystallographic studies revealed two polymorphs, 3- A and 3- B, exhibiting similar discrete molecular structures to those found for 1 and 2 but with different molecular arrangements. In agreement with the variable-temperature single-crystal X-ray diffraction, the magnetic susceptibility measurements, performed in the temperature range 2-400 K, showed a spin-crossover phenomenon above room temperature for complexes 1, 3- A, and 3- B with a T 1/2 of 336, 377, and 383 K, respectively, while complex 2 remains in the high-spin ground state ( S = 2) in the whole temperature range. To understand further the magnetic behaviors of 1, 3-A, and 3-B, single-crystal X-ray diffraction measurements were performed at high temperatures. The crystal structures of both polymorphs could not be obtained above 400 K because the crystals decomposed. However, single-crystal X-ray data have been collected for compound 1, which reaches the full high-spin state at lower temperatures. Its crystal structure, solved at 400 K, showed a strong modification of the iron coordination sphere (average Fe-N = 2.157(3) A vs 1.986(3) A at 293 K). In agreement with the magnetic properties. Such structural behavior is a signature of the spin-state transition from low-spin (LS) to high-spin (HS). On the basis of the intermolecular pi stacking observed for the series described in this paper and for related complexes involving similar discrete structures, we have shown that complexes displaying frontal pi stacking present spin transition such as 1, 3-A, and 3-B and those involving sideways pi stacking such as complex 2 remain in the HS state.

Novel Infinite Three‐Dimensional Networks with Highly Conjugated Polynitrile Ligands: Syntheses, Crystal Structures, and Magnetic Properties of [Cu{C[C(CN)2]3}(H2O)2]n and [Cu{C[C(CN)2]3}(en)]n (en=NH2CH2CH2NH2)

An unprecedented coordination mode for the highly conjugated cyanocarbanion [C{C(CN)2}3]2− (1) is observed in the title complexes. This ligand employs four of its six CN groups in a μ4-η4 bridging mode to form two unique three-dimensional polymers.

Photoinduced HS state in the first spin-crossover chain containing a cyanocarbanion as bridging ligand

A new polymeric approach, based on cyanocarbanion ligands, for the design of spin crossover (SCO) compounds led us to the compound [Fe(abpt)(2)(tcpd)] () (tcpd(2-) = (C[C(CN)(2)](3))(2-), abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) which has been characterised as the first SCO molecular chain involving a cyanocarbanion as bridging ligand.

Cyanocarbanion-based spin-crossover materials: photocrystallographic and photomagnetic studies of a new iron(II) neutral chain.

A new iron(II) chain of formula [Fe(abpt)(2)(tcpd)] [1; (tcpd)(2-) = [C(10)N(6)](2-) = (C[C(CN)(2)](3))(2-) = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide anion, abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole] has been synthesized and characterized by IR spectroscopy, detailed variable-temperature single-crystal X-ray diffraction, magnetic and photomagnetic measurements. The crystal structure determination of 1 reveals a one-dimensional structural architecture in which the (tcpd)(2-) cyanocarbanion acts as a μ(2)-bridging ligand and the two abpt molecules act as chelating ligands. Detailed X-ray diffraction studies as a function of the temperature (293-10 K) showed a strong modification of the iron coordination sphere, whose characteristics are in agreement with the presence of a spin-crossover transition from high spin (HS) to low spin (LS) in 1. The average Fe-N distances at room temperature, at 10 K following a flash cooling, and at 10 K after subsequent HS-to-LS relaxation are in the range expected for 100%, 50%, and 25% fractions of HS Fe(II), respectively. These observations are consistent with the presence of ca. 25% residual HS species at low temperatures, as derived from the magnetic data. The signature of a photoinduced metastable HS state in 1 has been detected by performing coupled photomagnetic and photocrystallographic analyses. The limiting T(LIESST) value associated with the light-induced excited-spin-state trapping effect was derived as 35 K, in good agreement with the thermal dependence of the unit cell volume upon irradiation. Kinetic studies governing the photoinduced HS/LS process have been recorded at different temperatures; a reverse-LIESST effect has been evidenced at 10 K as a reduction of the residual HS fraction by irradiating the sample at 830 nm.

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.

Comparison of the properties of the 1,1,2,4,5,5-hexacyano-3-aza-penta-1,4-dienide[(NC)2CC(CN)NC(CN)C(CN)2] unit as anion and as ligand. Crystal structures of (Et4N)(C10N7) and [{Ag(C10N7)}∞]

Abstract The previously reported compounds, Et 4 N(C 10 N 7 ), 1 , and [{Ag(C 10 N 7 )} ∞ ], 2 , have been structurally characterized by X-ray diffraction. The C 10 N 7 unit acts in 1 as a monoanion and in 2 as a sophisticated bridging ligand (via the nitrogen atoms of its four external cyanogroups) leading to a structure with two crystallographically distinct silver cations. The first one has an usual pseudo-tetrahedral coordination, the second one presents an unexpected square planar coordination which is discussed. The geometry of the organic fragment is only slightly modified upon coordination: in both cases, the C 10 N 7 unit is essentially planar with central CN bond lengths of 1.317(4) and 1.334(4) A in 1 , 1.33(1) and 1.34(1) A in 2 and CNC angles of 128.3(3) in 1 and 129.2(9)° in 2 . In benzonitrile solutions, the C 10 N 7 anion shows two one electron diffusion-controlled reversible reduction rocesses, the first one leading to the radical species [(C 10 N 7 )] 2− characterized by ESR.

{[CuII(tn)]2[FeII(CN)6]}·KCl·5H2O (tn = 1,3-diaminopropane): a two-dimensional bimetallic layered material with “Cu4Fe3” defective cubane units

The new two-dimensional coordination compound {[CuII(tn)]2[FeII(CN)6]}·KCl·5H2O (1) (tn=1,3-diaminopropane), generated by six –Fe–CN–Cu– bridges, shows weak ferromagnetic interactions between the nearest Cu(II) ions through the diamagnetic [Fe(CN)6]4− anion.

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.

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.

Radical salts of the organic donor BET-TTFwith polyoxometalate clusters

The synthesis, structures and physical characterizations of the first radical ion salts of the organic donor BET-TTF1 with polyoxometalate clusters ([M6O19 ]2– ; M=WVI , MoVI , 2) are reported. The 2:1 salts (BET-TTF+)2 [M6O19 ]2– are formed by pairs of the BET-TTF+ radical cations surrounded by polyanions so as to form a 3D packing of anions and cations with short intermolecular contacts between the cation pairs. The synthesis, physical properties and main structural features of the first radical ion salts of the organic donor BET-TTF 1 with the polyoxometalate cluster [SiW12O40 ]4–3 are also reported. The 4:1 salt (BET-TTF+)4 [SiW12O40 ]4– is formed by a 2D hexagonal packing of anions and by isolated BET-TTF+ pairs. The compounds are insulators and diamagnetic.