ABSTRACT
CO, CNR, R3P and NO are those ligands which have filled donor orbitals as well as empty π-orbitals. These ligands are called π-bonding ligands. They combine with transition metals in zero, –l and +1 oxidation states to form π-bonding complexes. These complexes exhibit ligand to metal L → M as well as metal to ligand M → L bonds. The compounds formed by CO and metal atom in –1, 0 and +1 oxidation states are called metal carbonyls.
