Coordination complexes are chemical structures formed when central metal atoms bond with surrounding molecules or ions, known as ligands. These ligands can be neutral molecules or charged ions that donate electron pairs to the metal, creating a stable arrangement. The central metal is typically a transition metal, which can accommodate various ligands due to its ability to change oxidation states. The geometry of coordination complexes can vary, leading to different shapes such as octahedral, tetrahedral, or square planar. The properties of these complexes, including color and reactivity, are influenced by the type of metal and ligands involved. Coordination complexes play essential roles in fields like bioinorganic chemistry and catalysis.