The reaction of copper(l) iodide with tri-m-tolylphosphine (m-tolyl(3)P) in acetonitrile yielded the cluster [Cu-6(mu(2)-l)(mu(3)-l)(4)(mu(4)-l)(m-tolyl(3)P)(4)(CH3CN)(2)] (1), with a bicapped adamantoid geometry. In this compound, four Cu atoms are coordinated to four terminally bonded m-tolyl(3)P ligands, two Cu atoms are bonded to two CH3CN ligands, and iodide ligands have mu(2)-l, mu(3)-l, and mu(4)-l bonding modes. This compound has four Cul(3)P and two Cul(3)N cores, and geometry around each Cu center is distorted tetrahedral. The polarizable iodide ligand and the position of the methyl group in the phenyl ring attached to the P atom appear to have played the pivotal role in the formation of monomeric bicapped adamantoid geometry, which is unique in copper chemistry.