Two new ternary manganese bismuthides have been synthesized and their structures established based on single-crystal X-ray diffraction methods. Sr2MnBi2 crystallizes hi the orthorhombic space group Pnma (a = 16.200(9) angstrom, b 14.767(8) angstrom, c = 8.438(5) angstrom, v = 2018(2) angstrom(3); Z = 12; Pearson index oP60) and is isostructural to the antimonide Sr2MnSb2. The crystal structure contains corrugated layers of corner- and edge-shared [MnBi4] tetrahedra and Sr atoms enclosed between these layers. Electronic structure calculations suggest that Sr2MnBi2 is a magnetic semiconductor possessing Mn2+ (high-spin d(5)) ions, and its structure can be rationalized within the Zintl concept as [Sr2+](2)[Mn2+][Bi3-](2). The temperature dependence of the resistivity shows behavior consistent with a degenerate semiconductor/poor metal, and magnetic susceptibility measurements reveal a high degree of frustration resulting, from the two-dimensional nature of the structure. The compositionally similar Ba2Mn1-xBi2 (x approximate to 0.15) crystallizes in a very different structure (space group Imma, a = 25.597(8) angstrom, b = 25.667(4) angstrom,c = 17.128(3) angstrom, V = 11253(4) angstrom(3); Z = 64; Pearson index oI316) with its own structure type. The complex structure boasts Mn atoms in a variety of coordination environments and can be viewed as consisting of two interpenetrating 3D frameworks, linked by Bi-Bi bonds. Ba(2)Mm(1-x)Bi(2) can be regarded as a highly reduced compound with anticipated metallic behavior.