The manganese phosphorus cluster [Mn5{N(SiMe3)2}{mu4-PSiiPr3}2{mu-P(H)SiiPr3}5] containing an unusual Mn5P7 core structure and three short Mn-Mn distances was obtained from the reaction of Mn{N(SiMe3)2}2 with H2PSiiPr3. Quantum chemical investigations indicated the presence of comparably strong intramolecular antiferromagnetic interactions leading to a total S = 5/2 spin ground state, which was confirmed by magnetic measurements.