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

The synthesis and crystal structure (100 K) of the title compound, [Fe(CHBrNOS)]NO·HO, is reported. The asymmetric unit consists of an octahedral [Fe(HL)] 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 FeSNO 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)](anion)·HO compound contains the first known cationic Fe entity containing two salicylaldehyde thiosemicarbazone derivatives. The Fe 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 ion with a zero-field splitting D = 0.439 (1) cm.