What do coordination complexes consist of in coordination chemistry?

Coordination complexes are defined as structures that consist of a central metal atom or ion bonded to surrounding molecules or ions known as ligands. In this context, the central metal, often a transition metal, plays a pivotal role in the complex by providing vacant orbitals to accommodate the electron pairs donated by the ligands.

Ligands can vary widely in their nature, including anions, neutral molecules, and even bi-dentate or multi-dentate species that can attach to the metal at multiple sites. This ability to coordinate with the metal enhances the stability and reactivity of the complex, and it is this bonding interaction that forms the foundation for many applications across various fields, including catalysis, materials science, and biological chemistry.

The other options do not accurately represent the nature of coordination complexes: they might reference specific components or types of substances but fail to encompass the defining characteristic of the central metal-ligand relationship. Therefore, the option identifying coordination complexes as a combination of a central metal atom and ligands captures the essence and structure of these complexes accurately.