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Hofmann-like cyanometallic complexes represent one of the biggest and well-known classes of FeIIspin-crossover compounds. In this paper, we report on the first FeIIHofmann clathrate analogues with unsubstituted 1,2,3-triazole, which exhibit temperature induced spin transition. Two new coordination polymers with the general formula [FeII(1,2,3-triazole)2MII(CN)4] (M = Pt, Pd) undergo abrupt hysteretic spin crossover in the range of 190–225 K as revealed by magnetic susceptibility measurements. Two compounds are isostructural and are built of infinite cyanometallic layers which are supported by 1,2,3-triazole ligands. The thermal hysteresis loop is very stable at different scan rates from 0.5 to 10 K min−1. The compounds display strong thermochromic effect, changing their colour from pink in the low-spin state to white in the high-spin state. Our findings show that 1,2,3-triazole is suitable for elaboration of spin-crossover Hofmann clathrate analogues, and its use instead of more classical azines can advantageously expand this family of complexes.

Two 2D Hofmann-type complexes of the composition [Fe(Phpz)

In the title polymeric coordination compound, {[FePt(CN)

International audience; Nucleation and growth phenomena associated with the thermally-induced spin transition was studied using optical microscopy in single crystals of a cyanoheterometallic coordination polymer [Fe(1,6-naphthyridine)2(Ag(CN)2)2]. Despite the fact that the spin-crossover phenomenon occurs near room temperature (ca. 290–300 K), the experimental results show the existence of significant kinetic effects on the hysteretic behaviour of the spin transition in this compound. Ultra-slow switching rates and phase-boundary propagation velocities were observed (down to 3 nm s−1), several orders of magnitude lower than customary. Our observations indicate that these peculiar spin-crossover properties (slow switching kinetics, scan-rate-dependent transition temperatures) are presumably related to the presence of numerous microstructural defects in the crystals, which is an intrinsic characteristic of this compound.

Two new 2D spin-crossover (SCO) analogues of Hofmann clathrates of composition [Fe(phth)2MII(CN)4] (where phth = phthalazine; MII= Pd, Pt) have been synthesized and their structures and switchable behaviour have been characterized. Single-crystal X-ray analysis reveals that the Pt and Pd derivatives contain FeIIcentres equatorially surrounded by four equivalent μ4-[MII(CN)4]2−groups. Two crystallographically equivalent phthalazine (phth) ligands occupy the axial positions of each FeIIsite, completing its octahedral coordination environment. The stabilization of these structures is realizedviasupramolecular C–H⋯M interactions and π–π stacking. Temperature-dependent magnetic susceptibility measurements showed that Pt (T1/2↓ = 211 K andT1/2↑ = 218 K) and Pd (T1/2↓ = 202 K andT1/2↑ = 207 K) derivatives display cooperative spin crossover with narrow thermal hysteresis loops. In addition, spin crossover in these complexes was characterized by optical measurements, differential scanning calorimetry, and IR and Raman spectroscopy. This research shows that the use of phthalazine leads to the production of new SCO systems with attractive transition characteristics and opens up new perspectives for the design of switchable complexes based on fused bicyclic azine ligands.

A new iron(II)-based spin-crossover compound with thermal hysteresis operating under ambient conditions is reported. This complex exhibits a high reproducibility of the spin transition in many successive thermal cycles, stability of both spin states at room temperature and an attractive operational temperature range.

The 1,2-bis­(pyridin-4-yl)ethene mol­ecules bridge FeII cations to form polymeric chains running along the a axis., In the title polymeric complex, {[Fe(C12H10N2)2(H2O)4](CH3C6H4SO3)2·2CH3OH}n, the FeII cation, located on an inversion centre, is coordinated by four water mol­ecules in the equatorial positions and two 1,2-bis­(pyridin-4-yl)ethene mol­ecules in the axial positions. This results in a distorted octa­hedral geometry for the [N2O4] coordination polyhedron. The 1,2-bis­(pyridin-4-yl)ethene mol­ecules bridge the FeII cations, forming polymeric chains running along the a-axis direction. Stabilization of the crystal structure is provided by O—H⋯O hydrogen bonds; these are formed by coordinated water mol­ecules as donors towards the O atoms of the methanol mol­ecules and tosyl­ate anions as acceptors of protons, leading to the formation of a three-dimensional supra­molecular network. Weak C—H⋯O hydrogen bonds are also observed in the crystal.

In the title polymeric complex, {[Fe(C12H10N2)2(H2O)4](CH3C6H4SO3)2·2CH3OH}n, the FeIIcation, located on an inversion centre, is coordinated by four water molecules in the equatorial positions and two 1,2-bis(pyridin-4-yl)ethene molecules in the axial positions. This results in a distorted octahedral geometry for the [N2O4] coordination polyhedron. The 1,2-bis(pyridin-4-yl)ethene molecules bridge the FeIIcations, forming polymeric chains running along thea-axis direction. Stabilization of the crystal structure is provided by O—H...O hydrogen bonds; these are formed by coordinated water molecules as donors towards the O atoms of the methanol molecules and tosylate anions as acceptors of protons, leading to the formation of a three-dimensional supramolecular network. Weak C—H...O hydrogen bonds are also observed in the crystal.