The coordination number of the complex [Fe CN 6]^4- is 6, as there are six cyanide CN ligands surrounding the central Fe II ion. The geometry of this complex is octahedral, which is a common geometry for complexes with a coordination number of 6.The presence of the cyanide ligands affects the electronic properties of the Fe II ion in the complex in several ways:1. Ligand field effect: The cyanide ligands create a ligand field around the Fe II ion, which splits the d-orbitals of the metal ion into two sets with different energies. In an octahedral complex, the d-orbitals are split into two groups: the lower-energy t2g set dxy, dyz, and dxz orbitals and the higher-energy eg set dz^2 and dx^2-y^2 orbitals . The energy difference between these two sets is called the crystal field splitting energy .2. Strong field ligand: Cyanide is a strong field ligand, meaning it causes a large crystal field splitting energy . As a result, the Fe II ion's d-electrons will preferentially occupy the lower-energy t2g orbitals before any electrons are placed in the higher-energy eg orbitals. This results in a low-spin configuration for the Fe II ion, which has a smaller magnetic moment and is less paramagnetic compared to a high-spin configuration.3. Charge and oxidation state: The cyanide ligands are negatively charged, and the overall charge of the complex is -4. This means that the Fe II ion has an oxidation state of +2, which affects its electronic configuration and reactivity.4. Back-bonding: Cyanide ligands are capable of -back-bonding, which involves the donation of electron density from the metal ion's filled d-orbitals to the empty * orbitals of the cyanide ligands. This back-bonding further stabilizes the complex and can affect its spectroscopic properties and reactivity.Overall, the presence of the cyanide ligands in the [Fe CN 6]^4- complex significantly influences the electronic properties of the Fe II ion, resulting in a low-spin, octahedral complex with unique spectroscopic, magnetic, and reactivity characteristics.