Non-innocent Intercalation of Diamines into Tetragonal FeS Superconductor

We report two solvothermal pathways toward intercalated iron sulfide, [Fe8S10]­Fe­(en)3·en0.5 (en = ethylenediamine), featuring [Fe8S10]2– layers stacked by [Fe­(en)3]2+ cations and free ethylenediamine molecules. [Fe8S10]­Fe­(en)3·en0.5 is synthesized in a simple single-step method from Fe and S in ethylenediamine with addition of NH4Cl mineralizer as well as from solvothermal treatment of mackinawite, tetragonal FeS. In situ synchrotron powder X-ray diffraction experiments reveal a clear transformation of tetragonal FeS into [Fe8S10]­Fe­(en)3·en0.5 upon reaction with ethylenediamine. In-house control synthetic experiments confirmed the chemical process, whereby ethylenediamine leaches iron solely from the tetragonal Fe–S layers to form [Fe­(en)3]2+ complexes and thereby oxidize the intralayer iron to Fe2.25+. Our report emphasizes that, in layered iron chalcogenides, diamines can intercalate as charged coordination complexes in tandem with neutral diamine molecules.