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

Abstract

A one-dimensional (1D) chain compound [Fe(en)3]3(FeSe2)4Cl2 (en = ethylenediamine), featuring tetrahedral FeSe2 chains separated by [Fe(en)3] 2+ cations and Clanions, 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. 57 Fe Mössbauer spectroscopy reveals the mixed-valent nature of [Fe(en)3]3(FeSe2)4Cl2 with Fe 3+ centers in the [FeSe2]chains and Fe 2+ centers in the [Fe(en)3] 2+ complexes. SQUID magnetometry indicates that [Fe(en)3]3(FeSe2)4Cl2 is paramagnetic with a reduced average effective magnetic moment, μeff, of 9.51 μB per formula, 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 Clions 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.

Non-innocent Intercalation of Diamines into Tetragonal FeS Superconductor

“…The conversion of FeS to [Fe 8 S 10 ]­Fe­(en) 3 ·en 0.5 was reproduced with handling chemicals and solvents and loading and opening autoclaves in an Ar-filled glovebox under air-free conditions, thus excluding oxygen as oxidizer. Ethylenediamine is known to exhibit substantial red/ox activity in the solvothermal synthesis of metal chalcogenides, , and we hypothesize that ethylenediamine gets reduced upon oxidation of Fe in the transformation of FeS into [Fe 8 S 10 ]­Fe­(en) 3 ·en 0.5 .…”

“…14) and is composed of [Fe 8 S 10 ] 2– square tetrahedral layers intercalated by [Fe­(en) 3 ] 2+ octahedral complexes as well as free ethylenediamine molecules ( a = 8.3633(5) Å, b = 33.225(2) Å, c = 20.543(1) Å, β = 90.111(1)°). The average Fe–N distance of 2.22(2) Å indicates a high-spin Fe 2+ ion in the [Fe­(en) 3 ] 2+ octahedral complex. , The layers themselves are like those in mackinawite FeS, but with one-fifth of the sites vacant in an ordered motif (Figure ), resulting in a √5 × 4√5 superstructure in the plane of the Fe–S layer and a ca. 5.2 Å increase in the interlayer spacing.…”

“…In situ synchrotron PXRD experiments conducted at beamline 17-BM-B at the Advanced Photon Source at Argonne National Laboratory were used to further investigate the structural transformation from FeS (mackinawite) to [Fe 8 S 10 ]Fe(en) 3 ·en 0.5 . Full details of the in situ synchrotron PXRD setup specific to solvothermal samples are described elsewhere . A few milligrams of FeS starting material were added to a silica capillary which was subsequently filled with ethylenediamine and pressurized with He to simulate solvothermal conditions.…”

“…In addition, diamines tend to coordinate the leached Fe, forming a second type of the intercalated species, positively charged chelating complexes, which can coexist with neutral diamine molecules in the interlayer space. Finally, we have recently shown that anions, such as chloride or bromide, may also be present in the interlayer space of complex layered Fe chalcogenides . Considering all the structural complexity, one should use caution while deriving any conclusions regarding the composition, structure of Fe-Ch layer or intercalate, or their correlation to properties based on routine PXRD patterns, which only provide information regarding the interlayer spacing.…”

“…Furthermore, diamine intercalates demonstrate a high degree of structural flexibility due to the reactivity of diamines, which have a high propensity to chelate transition metals, including Fe. , This propensity for iron can not only leach Fe from the Fe-Ch layers but also produce in situ new intercalating species, Fe-diamine chelation complexes. Iron migration from Fe-Ch layers to the interlayer space adds a particular challenge when finding the composition by spectroscopic methods such as energy dispersive X-ray spectroscopy.…”