(NH 3 (CH 2 ) 7 NH 3 ) 2 Sn 3 I 10 forms crystal structure best described as a perovskite derivative with ordered vacancies and three-dimensional inorganic connectivity. The structure exhibits corner-linked Sn(II) octahedra and square pyramids (e.g., Sn-centered octahedron with a missing ligand). The structure resembles that of a Dion-Jacobson derived structure, but with the [SnI 5 ] polyhedron bridging the [SnI 4 ] 2-layers of octahedra. This structure appears to be stabilized due to the similar sizes between diammoniumheptane and the I-Sn-I bond lengths. The optical and electronic properties reflect both the "defective" and 3D nature of the crystal structure. Time-resolved microwave conductivity experiments reveal carrier mobility consistent with a close-packed anionic substructure that yields a polaronlimited carrier mobility, as also found in the vacancy-ordered double perovskites (Cs 2 SnI 6 and (CH 3 NH 3 ) 2 SnI 6 ). Yet, the defect-like structure appears to yield rapid non-radiative recombination of photogenerated charge carriers generated with just-above band gap illumination, and the photoluminescence emission best resembles localized (e.g., single-ion) emitters in a deformable matrix. However, one significant outcome is that the vacancyordered crystal structure is not susceptible to the spontaneous tin vacancy formation compensated by high hole concentrations (e.g., "Sn(IV)") that plague most Sn(II) halide semiconductors. Understanding these crystal-chemical relationships motivates strategies for compositional engineering in emerging hybrid inorganic-organic optoelectronic materials and their devices.