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.
Yemeli
Eddy W T
EW
Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen (The Netherlands), Fax: (+31) 503634315. e.w.yemeli.tido@rug.nl.
Blake
Graeme R
GR
Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen (The Netherlands).
Douvalis
Alexios P
AP
Physics Department, University of Ioannina, 45110 Ioannina (Greece).
Bakas
Thomas
T
Physics Department, University of Ioannina, 45110 Ioannina (Greece).
Alberda van Ekenstein
Gert O R
GO
Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen (The Netherlands).
van Koningsbruggen
Petra J
PJ
Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen (The Netherlands), Fax: (+31) 503634315. p.j.van.koningsbruggen@rug.nl.|Chemical Engineering and Applied Chemistry, Aston University, Birmingham, B4 7ET (UK). p.j.van.koningsbruggen@rug.nl.