Tuning the Spin-Crossover Behaviour in Fe(II) Polymeric Composites for Food Packaging Applications

Abstract

Although the spin-crossover (SCO) phenomenon is well documented, tuning the SCO behaviour remains a challenging task. This could be mainly attributed to the ‘delicate’ nature of the phenomenon; cooperativity expressed through differences in particle size and morphologies, and electrostatic interactions could significantly affect the process. The goal of the present effort is dual bearing both scientific and technological interest. Firstly, to examine the technological potential of SCO complexes by incorporating them into polymers, and secondly—and most importantly—to investigate if polymer-SCO complex interactions could occur and could affect the SCO behaviour, depending on the structural properties of both the polymer matrix and the SCO complex. In this context, two different polymers, polylactic acid (PLA) and polysulphone (PSF), which are capable of developing different interactions with the inclusions, and the SCO complexes [Fe(abpt)2{N(CN)2}2] and [Fe(abpt)2(SCN)2] were examined; abpt is the N,N’-bidentate chelating ligand 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole. The composites were characterised through scanning electron microscopy (SEM), attenuated total reflectance infrared (ATR/FTIR), and Raman spectroscopy. In addition, the potential migration release of the SCO compounds from the polymeric matrices and their toxicity evaluation were also studied. In addition, the potential migration release of the SCO compounds from the polymeric matrices was evaluated, and their insignificant toxicity was also verified. Temperature-dependent Raman spectra were collected in situ for the monitoring of the SCO behaviour after the incorporation of the Fe(II) complexes into the polymers; an upshift of the T1/2 transition and a hysteretic behaviour was detected for PSF-SCO composites, compared with the non-hysteretic behaviour of the pristine SCO complexes.

Three novel mononuclear 4‐vinylpyridine‐based Fe(III) complexes displaying various spin‐crossover behaviour

“…[1][2][3][4][5][6][7][8] This phenomenon is not only of great significance in basic scientific research, but also has the potential to be widely applied in fields such as information storage, sensors, and molecular switches. [9][10][11][12][13][14][15][16][17] The transition temperature (T 1/2 ) of SCO compounds and the steepness, completeness, and hysteresis of the curve largely depend on the cooperation of spin centres. The magnitude of the cooperation depends on the way molecules are stacked in the lattice.…”

“…Spin crossover (SCO) refers to the phenomenon where transition metal ions with d 4 ‐d 7 electronic configurations can freely transition between high spin (HS) and low spin (LS) under certain conditions such as temperature, pressure, and magnetic field changes or light irradiation [1–8] . This phenomenon is not only of great significance in basic scientific research, but also has the potential to be widely applied in fields such as information storage, sensors, and molecular switches [9–17] . The transition temperature ( T 1/2 ) of SCO compounds and the steepness, completeness, and hysteresis of the curve largely depend on the cooperation of spin centres.…”

Supramolecular FeII4L4 cage for fast ammonia sensing

“…13 Our group reported two mononuclear high-spin (HS) complexes, [Fe II (trz-tet) 2 (H 2 O) 4 ]·4H 2 O (trz-tetH = 5-(4 H -1,2,4-triazol-yl)-2 H -tetrazole) and [Fe II (H 2 btm) 2 (H 2 O) 2 ]Cl 2 (H 2 btm = di(1 H -tetrazol-5-yl)methane), respectively, as colorimetric sensors for various volatile organic compounds and hazardous gases under ambient conditions, but with slow response to NH 3(g) . 14–17 In addition, some Fe based spin crossover MOFs and hybrid materials were also reported for gas sensing (H 2 O 18 and iodobenzene 19 ) and food packaging applications. 20…”

Selective Pathway toward Heteroleptic Spin-Crossover Iron(II) Complexes with Pyridine-Based N-Donor Ligands

“…Molecular complexes and frameworks that display this phenomenon became, in the last decades, a testbed , for the design of switchable materials that infiltrated many areas of material science and engineering. Such compounds, which often contain iron­(II) ions in an octahedral environment of N -donor ligands, , are exploited in molecular electronics, spintronics, − and straintronics, in manufacturing of multifunctional devices, , sensors, ,− and explosives, in medicinal diagnostics, − and food packaging . For them to function under ambient conditions in these applications, an SCO should be guided toward, Figure , room temperature by the molecular design. , …”