What characterizes coordination isomers?

Coordination isomers are characterized by having the same molecular formula but differing in the arrangement of ligands or coordination modes around a central metal ion. In this context, option C is correct because coordination isomers arise from differences in the bonding of ligands to the metal, which results in different structures despite having the same number and type of atoms.

For example, a coordination complex can have one ligand bonded through a donor atom (such as nitrogen in a coordination position) while another isomer may have that same ligand bonded through a different donor atom (like oxygen), leading to distinct structural isomers. Both forms share the same chemical formula, highlighting the point about different bonding orders contributing to isomerism.

The other options describe different concepts in coordination chemistry. Different donor atoms in the ligand would indicate different structural arrangements but does not differentiate between isomers of the same complex. Different ligands around the metal ion describe variations in the type of complex rather than isomerism. Different types of complex ions typically refer to distinct entities rather than clarifying variations within a specific isomeric form. Thus, option C accurately captures the essence of coordination isomers.