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Structure and Electronic Configuration of an Iron(II) Complex in a LIESST State: A Pump and Probe Method
Author(s) -
Sheu ChouFu,
Chen Kowa,
Chen SzuMiao,
Wen YuhSheng,
Lee GeneHsiang,
Chen JinMing,
Lee JyhFu,
Cheng BingMing,
Sheu HwoShuenn,
Yasuda Nobuhiro,
Ozawa Yoshiki,
Toriumi Koshiro,
Wang Yu
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200802279
Subject(s) - spin transition , spin crossover , crystallography , spin states , metastability , excited state , chemistry , triplet state , diamagnetism , crystal (programming language) , materials science , atomic physics , magnetic field , inorganic chemistry , physics , quantum mechanics , programming language , organic chemistry , computer science
Switchable molecules : The electronic configurations of the Fe center in trans ‐[Fe(tzpy) 2 (NCS) 2 ] in low‐spin, high‐spin, and LIESST states (LIESST=light‐induced excited spin‐state trapping) were confirmed by K‐ and L‐edge X‐ray absorption and magnetic measurements. The molecular structures at 40 K before and after irradiation are superimposed in the picture, which demonstrates a single‐crystal‐to‐single‐crystal transition by irradiation.Two polymorphs of mononuclear six‐coordinate iron(II) spin‐crossover complex trans ‐[Fe(tzpy) 2 (NCS) 2 ] (tzp y =3‐(2‐pyridyl)[1,2,3]triazolo[1,5‐ a ]pyridine) ( 1 ) were isolated and structurally characterized. According to the thermally dependent magnetic measurements, polymorph A undergoes a gradual spin transition from a paramagnetic high‐spin state ( 5 T 2 , S =2, HS‐1) above 200 K to a diamagnetic low‐spin state ( 1 A 1 , S =0, LS‐1) below 120 K, whereas polymorph B shows an abrupt spin transition with T 1/2 at 102 K. Molecular and crystal structures of polymorph A in the HS‐1 and LS‐1 states were studied at 300 and 40 K, respectively. Significant differences in FeN distances and coordination geometries of Fe were found between the two spin states, as expected. Light‐induced excited spin state trapping (LIESST) was observed upon irradiating the crystal with 532 nm laser light at 40 K, whereupon a metastable high‐spin state (HS‐2) was formed; the molecular and crystal structure of this metastable state were investigated by a pump and probe method because of its relatively fast relaxation. The electronic configuration of the Fe center in the HS‐1, LS‐1, and LIESST (HS‐2) states were further confirmed by Fe K‐ and L‐edge absorption spectroscopy. In addition, the CN stretching frequency on the ligand can also be followed through the spin transition. The excitation and relaxation process concerning such metastable state were followed by the CN stretching frequency and magnetic susceptibility measurements in the temperature ranges 15–55 K and 5–80 K, respectively. The structure and electronic configuration of the LIESST state of polymorph A were firmly established by X‐ray diffraction, X‐ray absorption, infrared absorption, and magnetic measurements. A single‐crystal‐to‐single‐crystal transition through irradiation was demonstrated. The changes in structure and electronic configuration as a result of the spin transition are believed to occur concurrently.