Two new dinuclear iron(II) complexes (
1·PF6 and
1·AsF6) of the general formula [Fe
II2(L2
C3)
2](X)
4·nH
2O·mMeCN (X = PF
6, n = m = 1.5 for
1·PF6 and X = AsF
6, n = 3, m = 1 for
1·AsF6) have been prepared and structurally characterized, where L2
C3 is a bis-1,2,3-triazolimine type Schiff-base ligand, 1,1′-[propane-1,3-diylbis(1
H-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 [Fe
II2(L2
C3)
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.
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