Systematic dimensional reduction of the layered β-FeSe structure by solvothermal synthesis.

Dimensional reduction of superconducting anti PbO-type iron selenide has been achieved by terminating the tetragonal square layers of FeSe tetrahedra by ethylenediamine (en) ligands. We obtained three new structures in the Fe-Se-en system. FeSe(en) contains FeSe single chains bridged via Fe(en) complexes. FeSe(en) has FeSe double strands separated by Fe(en) complexes and free en molecules. FeSe(en) conserves the tetragonal layers of bulk FeSe which are now widely separated by en molecules. Through systematic dilution of the solvent we were able to introduce an additional parameter in solvothermal synthesis and thus have control over the connectivity of the tetrahedra. Additionally, a phase diagram of the Fe-Se-en system is generated by variation of the reaction temperature. The magnetic properties of the FeSe derivatives range from superconductivity and antiferromagnetism to paramagnetism.