The specific metal ion present in the active site of hemoglobin is iron Fe . It is found in the ferrous state Fe2+ within the heme group, which is an essential component of hemoglobin. The heme group consists of a porphyrin ring with the iron ion at its center.The iron ion coordinates with the surrounding ligands in the following manner:1. Axial coordination: The iron ion forms two axial coordination bonds. One of these bonds is with the imidazole side chain of a histidine residue called the proximal histidine from the protein part of hemoglobin. The other axial position is available for binding with an external ligand, which is typically an oxygen molecule O2 in the case of hemoglobin.2. Equatorial coordination: The iron ion is also coordinated to the four nitrogen atoms of the porphyrin ring in a planar arrangement. These nitrogen atoms belong to the pyrrole subunits of the porphyrin ring, and they form a square planar geometry around the iron ion.When an oxygen molecule binds to the iron ion, the geometry of the iron-ligand complex changes from a square planar to a distorted octahedral arrangement. This change in geometry triggers a conformational change in the hemoglobin protein, which enables it to carry and release oxygen molecules efficiently.In summary, the iron ion Fe2+ in the active site of hemoglobin coordinates with the surrounding ligands through axial coordination with the proximal histidine residue and an oxygen molecule, and equatorial coordination with the nitrogen atoms of the porphyrin ring. This coordination plays a crucial role in the oxygen transport function of hemoglobin.