Tuning Fe–Se Tetrahedral Frameworks by a Combination of [Fe(en)3]2+ Cations and Cl– Anions

A one-dimensional (1D) chain compound [ Fe(en) 3 ] 3 ( FeSe 2 ) 4 Cl 2 (en = ethylenediamine), featuring tetrahedral FeSe2 chains separated by [Fe­(en)3]2+ cations and Cl– anions, has been synthesized by a low temperature solvothermal method using simple starting materials. The degree of distortion in the Fe–Se backbone is similar to previously reported compounds with isolated 1D FeSe2 chains. 57Fe Mössbauer spectroscopy reveals the mixed-valent nature of [Fe­(en)3]3(FeSe2)4Cl2 with Fe3+ centers in the [FeSe2]− chains and Fe2+ centers in the [Fe­(en)3]2+ complexes. SQUID magnetometry indicates that [ Fe(en) 3 ] 3 ( FeSe 2 ) 4 Cl 2 is paramagnetic with a reduced average effective magnetic moment, μeff = 9.51 μB per formula unit, and a negative Weiss constant, θ = −10.9(4) K, indicating antiferromagnetic (AFM) nearest neighbor interactions within the [FeSe2]− chains. Weak antiferromagnetic coupling between chains, combined with rather strong intrachain AFM coupling, leads to spin-glass behavior at low temperatures, as indicated by a frequency shift of the peak observed at 3 K in AC magnetic measurements. A combination of [Fe­(en)3]2+ and Cl– ions is also capable of stabilizing mixed-valent 2D Fe–Se puckered layers in the crystal structure of [Fe­(en)3]4(Fe14Se21)­Cl2, where Fe14Se21 layers have a unique topology with large open pores. Property measurements of [Fe­(en)3]4(Fe14Se21)­Cl2 could not be performed due to the inability to either grow large crystals or synthesize this material in single-phase form.