| Autor: |
Bhar K; Department of Chemistry, School of Chemical Sciences and Pharmacy, Central University of Rajasthan, NH-8, Bandarsindri, Ajmer Distt., Rajasthan-305817, India. anuj.sharma@curaj.ac.in., Guo W; Univ. Bordeaux, CNRS, Bordeaux INP, ICMCB, UMR 5026, 87 avenue du Dr A. Schweitzer, F-33600 Pessac, France. philippe.guionneau@u-bordeaux.fr., Gonidec M; Univ. Bordeaux, CNRS, Bordeaux INP, ICMCB, UMR 5026, 87 avenue du Dr A. Schweitzer, F-33600 Pessac, France. philippe.guionneau@u-bordeaux.fr., Nikhil Raj M V; Department of Chemistry, School of Chemical Sciences and Pharmacy, Central University of Rajasthan, NH-8, Bandarsindri, Ajmer Distt., Rajasthan-305817, India. anuj.sharma@curaj.ac.in., Bhatt S; Department of Chemistry, School of Chemical Sciences and Pharmacy, Central University of Rajasthan, NH-8, Bandarsindri, Ajmer Distt., Rajasthan-305817, India. anuj.sharma@curaj.ac.in., Perdih F; Faculty of Chemistry and Chemical Technology, University of Ljubljana, Vecna pot 113, PO Box 537, SI-1000 Ljubljana, Slovenia., Guionneau P; Univ. Bordeaux, CNRS, Bordeaux INP, ICMCB, UMR 5026, 87 avenue du Dr A. Schweitzer, F-33600 Pessac, France. philippe.guionneau@u-bordeaux.fr., Chastanet G; Univ. Bordeaux, CNRS, Bordeaux INP, ICMCB, UMR 5026, 87 avenue du Dr A. Schweitzer, F-33600 Pessac, France. philippe.guionneau@u-bordeaux.fr., Sharma AK; Department of Chemistry, School of Chemical Sciences and Pharmacy, Central University of Rajasthan, NH-8, Bandarsindri, Ajmer Distt., Rajasthan-305817, India. anuj.sharma@curaj.ac.in. |
| Abstrakt: |
We present herein a family of molecular cis -[Fe II (X-PPMA) 2 (NCS) 2 ]·H 2 O [4-X- N -(phenyl(pyridin-2-yl)methylene)aniline; X-PPMA; X = -Cl (1), -Br (2), and -CH 3 (3)] complexes that exhibit spin crossover behaviour above room temperature. Judiciously designed bidentate N-donor Schiff bases of 2-benzoylpyridine and para -substituted anilines in combination with Fe(NCS) 2 were used for the synthesis of complexes 1-3. The relatively strong ligand field of the Schiff bases stabilises the low spin state of iron(II) up to 300 K which is evident from magnetic measurements, room temperature Mössbauer spectra and crystallographic bond/angle distortion parameters. Interestingly, complexes 1-3 crystallize in a tetragonal system with either a P 4 3 2 1 2 or P 4 1 2 1 2 chiral space group from achiral building units due to the supramolecular helical arrangements of molecules through intermolecular (pyridine)C-H⋯C(NCS) interactions in the crystalline state. Complexes 1 and 2 exhibit complete, gradual and slightly irreversible spin crossover behaviour in the temperature range of 300-500 K with equilibrium temperatures ( T 1/2 ) 375 K (1) and 380 K (2). The spin state evolution of iron(II) in complexes 1 and 2 is monitored between 150 K and 450 K through variable temperature crystallographic studies in the warming mode. The structural data are in good agreement with the 94% (1) and 87% (2) high spin conversion of iron(II) at 450 K. At a high temperature (450 K), some minor irreversible ligand motion is noticed in complexes 1 and 2, in addition to a complete solvent loss that may induce the slight irreversibility of the spin crossover. On the other hand, complex 3 shows a complete and gradual spin crossover in the temperature range of 10-475 K with strong irreversible features. The equilibrium temperatures obtained upon first warming ( T 1/2 ↑) and second cooling ( T 1/2 ↓) are 375 K and 200 K, respectively. In complex 3, the loss of a water molecule triggers strong deviations in the spin crossover behaviour. Moreover, dehydrated complex 3 exhibits photoswitching LIESST effect with a relaxation temperature T(LIESST) = 60 K. |
