Retracted: Light-Induced Bistability in Iron(III) Spin-Transition Compounds of 5 X-Salicylaldehyde Thiosemicarbazone (X=H,Cl, Br)

The iron(III) spin-crossover compounds [Fe(Hthsa)(thsa)] ⋅ H₂O ( 1 ), [Fe(Hth5Clsa)(th5Clsa)₂] ⋅ H₂O ( 2 ), and [Fe(Hth5Brsa)(th5Brsa)₂] ⋅ H₂O ( 3 ) (H₂thsa=salicylaldehyde thiosemicarbazone, H₂th5Clsa=5-chlorosalicylaldehyde thiosemicarbazone, and H₂th5Brsa=5-bromosalicylaldehyde thiosemicarbazone) have been synthesized and their spin-transition properties investigated by magnetic susceptibility, Mössbauer spectroscopy, and differential scanning calorimetry measurements. The three compounds exhibit an abrupt spin transition with a thermal hysteresis effect. The more polarizable the substituent on the salicylaldehyde moiety, the more complete is the transition at room temperature with an increased degree of cooperativity. The molecular structures of 1 and 2 in the high-spin state are revealed. The occurrence of the light-induced excited-spin-state trapping phenomenon appears to be dependent on the substituent incorporated into the 5-position of the salicylaldehyde subunit. Whereas the compounds with an electron-withdrawing group (-Br or -Cl) exhibit light-induced trapped excited high-spin states with great longevity of metastability, the halogen-free compound does not, even though strong intermolecular interactions (such as hydrogen-bonding networks and π stacking) operate in the system. For compound 2 , the surface level of photoconversion is less than 35 %. In contrast, compound 3 displays full photoexcitation.     

Non-thermal Plasma as a Priming Tool to Improve the Yield of Pea in Outdoor Conditions

Seed priming is a pre-treatment of seeds leading to the improvement of their germination, the plant growth, and the product yield. In this study we investigated the possibility of the use of non-thermal plasma operating in atmospheric pressure air for seed priming with the objective to improve the yield of pea seeds. Two priming ways were used: an indirect way by using plasma activated water (PAW) generated by the transient spark discharge with water electrospray or the glow discharge batch treatment and a direct exposure of seeds to the pulsed corona discharge. After treatment, the seeds were planted in the outdoor field for about 14 weeks until harvest. The direct plasma treatment resulted in two key results: the strong effectiveness of the pulsed corona plasma improving the yield, and the long-term effect of the plasma seed treatment. The results of the indirect treatment showed that the pea plants from the seeds primed using PAW gained some improved growth parameters, especially the number of seeds per pod and the total number of seeds per plant. The scanning electron microscopy analysis showed that PAW and direct treatment induced some morphology changes at the surface of the pea seeds. This study documents a long-term effect of non-thermal plasma seed priming and contributes to the plasma agriculture applications by suggesting the implementation of non-thermal plasma direct or indirect treatments into the field.

     

Study of neutral Fe(III) complexes of pyridoxal-N-substituted thiosemicarbazone with desolvation-induced spin-state transformation above room temperature

The preparation and characterization of two new neutral ferric complexes with desolvation-induced discontinuous spin-state transformation above room temperature are reported. The compounds, [Fe(Hthpy)(thpy)].CH3OH.3H2O (1) and [Fe(Hmthpy)(mthpy)].2H2O (2), are low-spin (LS) at room temperature and below, whereas their nonsolvated forms are high-spin (HS), exhibiting zero-field splitting. In these complexes, Hthpy, Hmthpy, and thpy, mthpy are the deprotonated forms of pyridoxal thiosemicarbazone and pyridoxal methylthiosemicarbazone, respectively; each is an O,N,S-tridentate ligand. The molecular structures have been determined at 100(1) K using single-crystal X-ray diffraction techniques and resulted in a triclinic system (space group P1) and monoclinic unit cell (space group P21/c) for 1 and 2, respectively. Structures were refined to the final error indices, where RF = 0.0560 for 1 and RF = 0.0522 for 2. The chemical inequivalence of the ligands was clearly established, for the "extra" hydrogen atom on the monodeprotonated ligands (Hthpy, Hmthpy) was found to be bound to the nitrogen of the pyridine ring. The ligands are all of the thiol form; the doubly deprotonated chelates (thpy, mthpy) have C-S bond lengths slightly longer than those of the singly deprotonated forms. There is a three-dimensional network of hydrogen bonds in both compounds. The discontinuous spin-state transformation is accompanied with liberation of solvate molecules. This is evidenced also from DSC analysis. Heat capacity data for the LS and HS phases are tabulated at selected temperatures, the values of the enthalpy and entropy changes connected with the change of spin state were reckoned at DeltaH = 12.5 +/- 0.3 kJ mol-1 and DeltaS = 33.3 +/- 0.8 J mol-1 K-1, respectively, for 1 and DeltaH = 6.5 +/- 0.3 kJ mol-1 and DeltaS = 17.6 +/- 0.8 J mol-1 K-1, respectively, for 2.