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 FeSe 2 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 FeSe 2 chains. 57 Fe Mössbauer spectroscopy reveals the mixed-valent nature of [Fe(en) 3 ] 3 (FeSe 2 ) 4 Cl 2 with Fe 3+ centers in the [FeSe 2 ] - chains and Fe 2+ centers in the [Fe(en) 3 ] 2+ complexes. SQUID magnetometry indicates tha [ Fe(en) 3 ] 3( FeSe 2 ) 4 Cl 2 is paramagnetic with a reduced average effective magnetic moment, μ eff = 9.51 μ B per formula unit, and a negative Weiss constant, θ = -10.9(4) K, indicating antiferromagnetic (AFM) nearest neighbor interactions within the [FeSe 2 ] - chains. Weak antiferromagnetic coupling between chains, combined with rather strong intra chain 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 (Fe 14 Se 21 )Cl 2 , where Fe 14 Se 21 layers have a unique topology with large open pores. Property measurements of [Fe(en) 3 ] 4 (Fe 14 Se 21 )Cl 2 could not be performed due to the inability to either grow large crystals or synthesize this material in single-phase form.