Ligands form bonds with transition metals through a process known as coordinate bonding, also referred to as dative covalent bonding.

In chemistry, ligands are ions or molecules that can donate a pair of electrons to a transition metal, resulting in the formation of a complex. This process, called coordinate bonding, is distinctive because transition metals possess vacant d-orbitals, which allow them to accept these electron pairs from ligands.

Unlike typical ionic or covalent bonds, the bond formed between ligands and transition metals is a specific type of covalent bond where both electrons originate from the same atom, the ligand. This unique characteristic is why it is also termed a dative bond. Ligands can vary in structure, ranging from simple ions, such as the chloride ion ($\text{Cl}^-$), to complex molecules, like water ($\text{H}_2\text{O}$), which possess lone pairs of electrons available for donation to the transition metal.

The capacity of a transition metal to bond with ligands is determined by its coordination number, which indicates the number of ligand attachment sites available on the metal. For instance, in a hexaaqua complex, the coordination number is $6$, signifying that six water molecules can coordinate to the central metal ion.

The specific types of ligands and their spatial arrangement around the transition metal significantly influence the properties of the resulting complex. A notable example is the color of transition metal complexes, which often arises from the absorption of specific wavelengths of light by the d-orbitals of the metal ion. When a ligand bonds to the metal, it induces a splitting of the d-orbitals into different energy levels, enabling the absorption of light at particular energies, which contributes to the observed color of the complex.

In conclusion, ligands bond with transition metals through coordinate bonding, where the ligand donates a pair of electrons to the metal’s vacant d-orbitals. The number, type, and arrangement of ligands around the metal are critical factors that can significantly influence the properties of the resulting complex.