Ammonium bis(salicylaldehyde thiosemicarbazonato)ferrate(III), a supramolecular material containing low-spin FeIII

Abstract

The synthesis and crystal structure (100 K) of the title compound, ammonium bis[salicylaldehyde thiosemicarbazonato(2-)-κ³O,N¹,S]iron(III), NH₄[Fe(C₈H₇N₃OS)₂], is reported. The asymmetric unit consists of an octahedral [Fe^III(thsa)₂]^- fragment, where thsa^2- is salicylaldehyde thiosemicarbazonate(2-), and an NH₄⁺ cation. Each thsa^2- ligand binds via the thiolate S, the imine N and the phenolate O donor atoms, resulting in an Fe^IIIS₂N₂O₂ chromophore. The ligands are orientated in two perpendicular planes, with the O and S atoms in cis and the N atoms in trans positions. The Fe^III ion is in the low-spin state at 100 K. The crystal structure belongs to a category I order-disorder (OD) family. It is a polytype of a maximum degree of order (MDO). Fragments of the second MDO polytype lead to systematic twinning by pseudomerohedry.

Keywords: MDO; ammonium; crystal structure; iron(III); low spin; maximum degree of disorder; order-disorder.