complex ion

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An ion formed by joining independent molecules or ions to a central metallic atom by coordinate bonds.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry any ion containing more than one atom. e.g. sulphate as opposed to sulphide
• noun chemistry any ion in which a central metal atom (normally a transition element) is surrounded by a group of ions or molecules (ligands). e.g. ferricyanide