Fe III in a high-spin state in bis(5-bromosalicylaldehyde 4-ethylthiosemicarbazonato-κ 3 O,N 1 ,S)ferrate(III) nitrate monohydrate, the first example of such a cationic Fe III complex unit.

The synthesis and crystal structure (100 K) of the title compound, [Fe(C 10 H 11 BrN 3 OS) 2 ]NO 3 ·H 2 O, is reported. The asymmetric unit consists of an octahedral [Fe III (HL) 2 ] + cation, where HL - is H-5-Br-thsa-Et or 5-bromosalicylaldehyde 4-ethylthiosemicarbazonate(1-) {systematic name: 4-bromo-2-[(4-ethylthiosemicarbazidoidene)methyl]phenolate}, a nitrate anion and a noncoordinated water molecule. Each HL - ligand binds via the thione S, the imine N and the phenolate O atom, resulting in an Fe III S 2 N 2 O 2 chromophore. The ligands are orientated in two perpendicular planes, with the O and S atoms in cis and the N atoms in trans positions. This [Fe(HL) 2 ](anion)·H 2 O compound contains the first known cationic Fe III entity containing two salicylaldehyde thiosemicarbazone derivatives. The Fe III ion is in the high-spin state at 100 K. In addition, a comparative IR spectroscopic study of the free ligand and the ferric complex is presented, demonstrating that such an analysis provides a quick identification of the degree of deprotonation and the coordination mode of the ligand in this class of metal compounds. The variable-temperature magnetic susceptibility measurements (5-320 K) are consistent with the presence of a high-spin Fe III ion with a zero-field splitting D = 0.439 (1) cm -1 .