121
The loss of two 4s electrons and one 3d electron forms the Fe
3+
ionic state. In this
form, due to five unpaired electrons in 3d orbital the spin of the ion is high, called
high spin ion which is an unstable form. If this ion forms a complex with three
bidentate ligands, then six an empty orbitals are required on the metal to receive the
six coordinated lone pairs of electrons. To form this complex, the valence (outer)
orbitals one 4s, three 4p (4 px , 4 py , 4 pz ) and two 4d ( 4 2 2
d x y
−
, 4 2
d z ) orbitals get hybridised to give a set of six equivalent sp
3
d
2
hybrid orbitals. A ligand orbital of oxygen
(hexadentate hydroxamate ions) each with a lone pair of electrons makes a coordinate (dative bond) with these empty hybridised orbitals of Fe
3+
metal ion and forms
an octahedral structure of the complex.
Fig. 8.2 Hydroxamate (left) and α-hydroxycarboxylate (right) bidentate ion ligands resonating
forms
Fig. 8.3 Origin of the basic unit, N
5 -hydroxy-N
5 -acylornithine of fungal siderophores
8 Chemistry and Biomedical Applications of Fungal Siderophores