(A \mathrm{Mn}{2} \mathrm{P}{2}(A=\mathrm{Sr}, \mathrm{Ba})) is an example of a composition that can assume a different structure type depending on the identity of the cation. (\mathrm{BaMn}{2} \mathrm{P}{2}) crystallizes in the (\mathrm{ThCr}{2} \mathrm{Si}{2}) structure type ((14 / \mathrm{mmm})), and (\mathrm{SrMn}{2} \mathrm{P}{2}) crystallizes in the (\mathrm{CaAl}{2} \mathrm{Si}{2}) structure type ( (P \overline{3} m 1)). Temperature-dependent magnetic susceptibility, neutron diffraction, and resistivity measurements were obtained for the two compounds. Neutron diffraction shows that (\mathrm{BaMn}{2} \mathrm{P}{2}) exhibits long-range antiferromagnetic ordering at room temperature. (\mathrm{Mn}) (II) is high spin, with ordered moment 4.2 (1) (\mu_{\mathrm{B}}), and the magnetic structure is type G. Magnetic susceptibility measurements show no maxima up to (750 \mathrm{~K}), indicating that the transition temperature, (T_{\mathrm{c}}), is very high. (\mathrm{SrMn}{2} \mathrm{P}{2}) is antiferromagnetic below (T_{\mathrm{c}}=53(1) \mathrm{K}), as determined from the temperature dependence of the magnetic reflections. There are two distinct sets of magnetic reflections distinguished by different temperature dependencies and indexing schemes. The magnetic structure is evidently complex, but was not determined. Both compounds exhibit semiconducting resistivity behavior with (E_{\mathrm{a}}=) (0.073(1) \mathrm{eV}\left(\mathrm{BaMn}{2} \mathrm{P}{2}\right)) and (0.0129(2) \mathrm{eV}\left(\mathrm{SrMn}{2} \mathrm{P}{2}\right)). The properties of (\mathrm{BaMn}{2} \mathrm{P}{2}) and (\mathrm{SrMn}{2} \mathrm{P}{2}) are discussed in light of their structures and previous theoretical investigations by Zheng and Hoffmann. 1994 Academic Press, Inc.