Large magnesium hydride aggregates [Mg13(Me3TACD)6(μ2‐H12)(μ3‐H6)][A]2 ((Me3TACD)H=1,4,7‐trimethyl‐1,4,7,10‐tetraazacyclododecane; A=AlEt4, AlnBu4, B{3,5‐(CF3)2C6H3}4) were synthesized stepwise from alkyl complexes [Mg2(Me3TACD)R3] (R=Et, nBu) and phenylsilane in the presence of additional MgII ions. The central magnesium atom is octahedrally coordinated by six hydrides as in solid α‐MgH2 of the rutile type. Further coordination to six magnesium atoms leads to a substructure of seven edge‐sharing octahedra as found in the hexagonal layer of brucite (Mg(OH)2). Upon protonolysis in the presence of 1,2‐dimethoxyethane (DME), this cluster was degraded into a tetranuclear dication [Mg2(Me3TACD)(μ‐H)2(DME)]2[A]2.