Abstract
Two new dinuclear iron(II) complexes (1·PF6 and 1·AsF6) of the general formula [FeII2(L2C3)2](X)4·nH2O·mMeCN (X = PF6, n = m = 1.5 for 1·PF6 and X = AsF6, n = 3, m = 1 for 1·AsF6) have been prepared and structurally characterized, where L2C3 is a bis-1,2,3-triazolimine type Schiff-base ligand, 1,1′-[propane-1,3-diylbis(1H-1,2,3-triazole-1,4-diyl)]bis{N-[2-(pyridin-2-yl)ethyl]methanimine}. Single crystal X-ray structure analyses revealed that 1·PF6 and 1·AsF6 are isostructural. The complex-cation [FeII2(L2C3)2]4+ of both has the same dinuclear double helicate architecture, in which each iron(II) center has an N6 octahedral coordination environment. Neighboring helicates are connected by intermolecular π–π interactions to give a chiral one-dimensional (1D) structure, and cationic 1D chains with the opposite chirality exist in the crystal lattice to give a heterochiral crystal. Magnetic and differential scanning calorimetry (DSC) studies were performed only for 1·AsF6, since the thermal stability in a high-temperature spin crossover (SCO) region of 1·PF6 is poorer than that of 1·AsF6. 1·AsF6 shows an unsymmetrical hysteretic SCO between the low-spin–low-spin (LS–LS) and high-spin–high-spin (HS–HS) states at above room temperature. The critical temperatures of warming (Tc↑) and cooling (Tc↓) modes in the abrupt spin transition area are 485 and 401 K, respectively, indicating the occurrence of 84 K-wide thermal hysteresis in the first thermal cycle.
Highlights
IntroductionThe interconversion between a high-spin (HS) and a low-spin (LS) state, the so-called “spin crossover” (SCO), is one of the most attractive phenomena in the field of molecular bistability [1,2,3]
The interconversion between a high-spin (HS) and a low-spin (LS) state, the so-called “spin crossover” (SCO), is one of the most attractive phenomena in the field of molecular bistability [1,2,3].This phenomenon is observed in 3d4 –3d7 transition metal complexes with various coordination geometries [1,4,5,6,7], and is triggered by an external stimulus such as temperature, pressure, light irradiation, or a magnetic field [1,2,3]
The ligand L2C3 was prepared stoichiometric by the 1:2 condensation reaction of 1,1′-(propaneThe ligand L2C3 was prepared stoichiometric by the 1:2 condensation reaction of 1,10 -(propane1,3-diyl)bis(1H-1,2,3-triazole-4-carbaldehyde) (4) and 2-(2-aminoethyl)pyridine. 4 was synthesized
Summary
The interconversion between a high-spin (HS) and a low-spin (LS) state, the so-called “spin crossover” (SCO), is one of the most attractive phenomena in the field of molecular bistability [1,2,3]. This phenomenon is observed in 3d4 –3d7 transition metal complexes with various coordination geometries (e.g., octahedral, square-pyramidal, trigonal-bipyramidal, tetrahedral, etc.) [1,4,5,6,7], and is triggered by an external stimulus such as temperature, pressure, light irradiation, or a magnetic field [1,2,3].
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