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)] (1) (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.Gomez Garcia, Carlos Jose, [email protected]

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)

International audienceNew 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(OCH3)C(CN)2]− = 1,1,3,3-tetracyano-2-methoxypropenide anion; tcnoet− = [(NC)2CC(OC2H5)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 T1/2 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) Å vs 1.986(3) Å 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 π stacking observed for the series described in this paper and for related complexes involving similar discrete structures, we have shown that complexes displaying frontal π stacking present spin transition such as 1, 3-A, and 3-B and those involving sideways π stacking such as complex 2 remain in the HS state

Guidelines to design new spin crossover materials

International audienceThis review focuses on new families of spin crossover (SCO) complexes based on polynitrile anions as new anionic ligands or on polyazamacrocycles as neutral macrocyclic ligands. We have shown that the structural and electronic characteristics (original coordination modes and high electronic delocalization) of the polynitrile anions can be tuned by slight chemical modifications such as substitution of functional groups or variation of the negative charge to design new discrete or polymeric SCO systems.In our ongoing work on the design of new molecular systems based on new ligands that can be fine-tuned via chemical modifications, another promising way which has been recently developed in our group concerns the use of new neutral polydentate ligands which are able to tune the ligand field energy around the metal centre. Here we report some recent original Fe(II) SCO complexes based on such polydentate ligands

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

Amantadine use in the French prospective NS-Park cohort

International audienceObjective: To assess amantadine use and associated factors in the patients with Parkinson's disease (PD).Background: Immediate-release amantadine is approved for the treatment of PD and is largely used in clinical practice to treat "levodopa-induced dyskinesia (LIDs). Its use varies according to countries and PD stages. The prospective NS-Park cohort collects features of PD patients followed by 26 French PD Expert Centres.Methods: Variables used for the analyses included demographics, motor and non-motor PD symptoms and motor complications [motor fluctuations (MFs), LIDs)], antiparkinsonian pharmacological classes and levodopa equivalent daily dose (LEDD). We evaluated: (i) prevalence of amantadine use and compared clinical features of amantadine users vs. non-users (cross-sectional analysis); (ii) factors associated with amantadine initiation (longitudinal analysis); (iii) amantadine effect on LIDs, MFs, apathy, impulse control disorders and freezing of gait (Fog) (longitudinal analysis).Results: Amantadine use prevalence was 12.6% (1,585/12,542, median dose = 200 mg). Amantadine users were significantly younger, with longer and more severe PD symptoms, greater LEDD and more frequent use of device-aided/surgical treatment. Factors independently associated with amantadine initiation were younger age, longer PD duration, more frequent LIDs, MFs and FoG, higher LEDD and better cognitive function. 9 of the 658 patients on amantadine had stopped it at the following visit, after 12-18 months (1.3%). New users of amantadine presented a higher improvement in LIDs and MF compared to amantadine never users.Conclusions: About 12% of PD patients within the French NS-Park cohort used amantadine, mostly those with younger age and more severe PD. Amantadine initiation was associated with a subsequent reduction in LIDs and MFs