title: Multifunctional mononuclear bisthienylethene-cobalt(II) complexes: structures, slow magnetic relaxation and photochromic behavior.
abstract: Based on two new bisthienylethenes containing N,O-donor binding sites, 2-(2-hydroxy-5-bromo-phenyl)-4,5-bis(2,5-dimethyl(3-thienyl))-1H-imidazole (BrLH) and 2-(2-hydroxy-5-diethylphosphono-phenyl)-4,5-bis(2,5-dimethyl(3-thienyl))-1H-imidazole (PLH), multifunctional mononuclear complexes Co(BrL)2·3CH3OH (1) and Co(PL)2·2CH3OH (2) have been synthesized and characterized by crystallographic analysis. In the molecular structures of 1 and 2, the Co(II) ion adopts a distorted tetrahedral coordination geometry, and is coordinated by two nonequivalent bisthienylethene molecules (BrL− in 1, PL− in 2), showing non-photoactive parallel and photoactive antiparallel conformations, respectively. Compounds 1 and 2 show a distinct distortion of Co(II) coordination geometry, with bond angles of N–Co–N = 112.71(12)° and O–Co–O = 99.87(11)° for 1 and N–Co–N = 119.93(12)° and O–Co–O = 107.31(13)° for 2. Thus, 1 and 2 revealed different magnetic behaviors, which are demonstrated by the χMT vs. T plots, and the frequency dependence of the χ′M and χ′′M signals at low temperature. Besides the field-induced slow magnetic relaxation, both 1 and 2 also showed photochromic behavior. Upon irradiation with 360 nm light for 1 and 343 nm light for 2, their CH2Cl2–CH3CN solutions could change color from being nearly colorless to blue purple. It was demonstrated that the substituent groups of Br atom and –PO(OEt)2 in 1 and 2, respectively, could significantly influence their crystal structures, magnetic relaxations and photochromic properties.
authors.affiliation: State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, P. R. China. dkcao@nju.edu.cn.
authors.forename: Deng-Ke
authors.initials: DK
authors.lastname: Cao
authors.forename: Ruo-Hong
authors.initials: RH
authors.lastname: Wei
authors.forename: Xiao-Xiong
authors.initials: XX
authors.lastname: Li
authors.forename: Yan-Wei
authors.initials: YW
authors.lastname: Gu