Where there are more than two centres that are bridged a bridging index is added as a subscript. For example in basic beryllium acetate which can be visualised as a tetrahedral arrangement of Be atoms linked by 6 acetate ions forming a cage with a central oxide anion, the formula and name are as follows:
:[Be(μ-O)(μ-OCMe)]
:hexakis(μ-acetato-κO:κ)-μ-oxido-tetrahedro-tetraberyllium
The μ describes the bridging of the central oxide ion. (Note the use of the kappa convention to describe the bridging of the acetate ion where both oxygen atoms are involved.) In the name where a ligand is involved in different modes of bridging, the multiple bridging is listed in decreasing order of complexity, e.g. μ bridging before μ bridging.