Mixed-Valence Iron(II, III) Trimesates with Open Frameworks Modulated by Solvents

Solvothermal reactions with different solvents produced two iron trimesates [Fe2(H2O)2(BTC)4/3]Cl·4.5(DMF) (1)
and [Fe4Cl(BTC)8/3]Cl2·H2O·2.5(DEF) (2) (BTC = 1,3,5-benzenetricarboxylate, DMF = N,N‘-dimethylformamide,
DEF = N,N‘-diethylformamide). The framework of 1 is a (3,4)-connected net constructed from mixed-valence
paddlewheel Fe2(II, III) units and BTC linkers, while the framework of 2 is a (3,8)-connected net built from mixed-valence square-planar Fe4(III, III, III, II) units and BTC linkers. The large volume inside the framework of 1 (or 2)
is occupied by disordered Cl- anions and guest DMF (or DEF) molecules. The mixed-valence character of the
frameworks of 1 and 2 was confirmed by Mössbauer spectroscopy studies. The active electronic property of iron
cations may be the origin of the variability of the iron−organic frameworks, which are readily affected by some
synthetic factors, such as solvents. Magnetic studies reveal that there are antiferromagnetic exchange interactions
among the Fe atoms in 1 and 2. Ion-exchange studies for 1 show that the Cl- anions inside the framework of 1
can be exchanged by CNS- anions.