FeIII in a high-spin state in bis(5-bromosalicylaldehyde 4-ethylthiosemicarbazonato-κ3O,N1,S)-ferrate(III) nitrate monohydrate, the first example of such a cationic FeIII complex unit

The synthesis and crystal structure (100 K) of the title compound, [Fe(C10H11Br-N3OS)(2)]NO3 center dot H2O, 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 (FeS2N2O2)-S-III 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)center dot H2O 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).