The title compound was found to crystallize in the Pu3Pd5 structure type (SG Cmcm) with cell dimensions of a = 10.5179(9) angstrom, b = 8.4789(8) angstrom, and c = 10.7623(10) angstrom. The structure consists of isolated Sn-5(6-) square-pyramidal units surrounded by cations that seem to play a crucial role in stabilizing the Zintl polyanions. The square pyramids contract at low temperatures (100 K) leading to the shortening of the basal intracluster Sn-Sn bond (2.74 angstrom), while the intercluster bonds become very large, indicating features of bond stretching isomerism as is known for Ba3Ge4. study of different crystals shows a slight variation in the lattice parameters, suggesting the presence of a definite phase width which was substantiated by the successful synthesis of monophasic samples of Sr3-xCaxSn5 (0.5 <= x <= 2.5). However, all attempts to obtain the pure Ca phase, Ca3Sn5 have been unsuccessful. The compounds show a weakly metallic behavior, as shown by the electrodeless Q method. Magnetic studies show a very low susceptibility (nearly temperature independent till 5 K). Our studies suggest that the "Sn" polyanions in Ca2.04Sr0.96Sn5 may be described as an arachno-Sn-5(-6) Zintl cluster.