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Spatiotemporal Studies of the One‐Dimensional Coordination Polymer [Fe(ebtz)2(C2H5CN)2](BF4)2: Tug of War between the Nitrile Reorientation Versus Crystal Lattice as a Tool for Tuning the Spin Crossover Properties

Authors :
Książek, Maria
Weselski, Marek
Kaźmierczak, Marcin
Tołoczko, Aleksandra
Siczek, Miłosz
Durlak, Piotr
Wolny, Juliusz A.
Schünemann, Volker
Kusz, Joachim
Bronisz, Robert
Source :
Chemistry - A European Journal. 11/11/2020, Vol. 26 Issue 63, p14419-14434. 16p.
Publication Year :
2020

Abstract

Reaction of 1,2‐di(tetrazol‐2‐yl)ethane (ebtz) with Fe(BF4)2⋅6 H2O in different nitriles yields one‐dimensional coordination polymers [Fe(ebtz)2(RCN)2](BF4)2⋅nRCN (n=2 for R=CH3 (1) and n=0 for R=C2H5 (2) C3H7 (3), C3H5 (4), CH2Cl (5)) exhibiting spin crossover (SCO). SCO in 1 and 3–5 is complete and occurs above 160 K. In 2, it is shifted to lower temperatures and is accompanied by wide hysteresis (T1/2↓=78 K, T1/2↑=123 K) and proceeds extremely slowly. Isothermal (80 K) time‐resolved single‐crystal X‐ray diffraction studies revealed a complex nature for the HS→LS transition in 2. An initial, slow stage is associated with shrinkage of polymeric chains and with reduction of volume at 77 % (in relation to the difference between cell volumes VHS−VLS) whereas only 16 % of iron(II) ions change spin state. In the second stage, an abrupt SCO occurs, associated with breathing of the crystal lattice along the direction of the Fe–nitrile bonds, while the nitriles reorient. HS→LS switching triggered by light (808 nm) reveals the coupling of spin state and nitrile orientation. The importance of this coupling was confirmed by studies of [Fe(ebtz)2(C2H5CN/C3H7CN)2](BF4)2 mixed crystals (2 a, 2 b), showing a shift of T1/2 to higher values and narrowing of the hysteresis loop concomitant with an increase of the fraction of butyronitrile. This increase reduces the capability of nitrile molecules to reorient. Density functional theory (DFT) studies of models of 1–5 suggest a particular possibility of 2 to adopt a low (140–145°) value of its Fe‐N‐C(propionitrile) angle. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
09476539
Volume :
26
Issue :
63
Database :
Academic Search Index
Journal :
Chemistry - A European Journal
Publication Type :
Academic Journal
Accession number :
146976087
Full Text :
https://doi.org/10.1002/chem.202002460