Dimanganese decacarbonyl reacts with trimethylaluminum in a mixture of hexane and tetrahydrofuran to produce [Mn][Mn-7(THF)(6)(CO)(12)](2) (1; THF = tetrahydrofuran) and the unstable compounds Mn-3(THF)(2)(CO)(10) (2) and [Mn(THF)(6)][Mn(CO)(5)](2) (3). The crystal structure of 1 is made up of two Mn-7(THF)(6)(CO)(12)(-) anions, each of which is coordinated to an isolated Mn2+ cation via three carbonyl oxygens to give an octahedral coordination geometry about the cation, The framework of each Mn-7(THF)(6)(CO)(12)(-) anion consists of a ring of six manganese atoms, all of which are attached to a seventh manganese in the center of the ring to form a planar Mn-7 unit. The six-membered ring is made up of alternating Mn(CO)(4) and Mn(THF)(2) groups, and if metal-metal bonds to the central manganese are ignored, the former have approximate octahedral coordination while the latter have somewhat distorted tetrahedral geometries.