The prototypal hexacoordinate C (phC) mol., CB62- (D6h), can be annulated by inserting arenes, olefins, or other one or two atom bridging groups into a perimeter B-B bond. Two single-atom units also can bridge opposite CB6 edges. These strategies allow the design of limitless phC derivs. based on CB6 as a building block unit. Illustrative examples, shown to be viable computationally, offer possibilities for exptl. realization. These phC's involve multicenter deltahedral sigma bonding, common for B but unusual for C, in the ring planes, as well as pi delocalization. [on SciFinder (R)]