The splitting of the d orbitals in an octahedral field takes palce in such a way that \(dx^2-y^2,dz^2\) , experience a rise in energy and form the \(e_g\) level, while \(dxy, dyz\) and \(dzx\) experience a fall in energy and form the \(t_{2g}\) level.
A coordination compound holds a central metal atom or ion surrounded by various oppositely charged ions or neutral molecules. These molecules or ions are re-bonded to the metal atom or ion by a coordinate bond.
A coordination entity composes of a central metal atom or ion bonded to a fixed number of ions or molecules.
A molecule, ion, or group which is bonded to the metal atom or ion in a complex or coordination compound by a coordinate bond is commonly called a ligand. It may be either neutral, positively, or negatively charged.