The structures of the strontium polyhydrides, with n

2, under pressure are studied using evolutionary algorithms coupled with density functional theory calculations. A number of phases with even n are found to be thermodynamically stable below 150 GPa. Particularly interesting is the stoichiometry, which comprises the convex hull at 50, 100, and 150 GPa. Its hydrogenic sublattice contains and units, and throughout the pressure range considered, it adopts one of two configurations which were previously predicted for CaH_{4} under pressure. At 150 GPa, the stoichiometry has the lowest enthalpy of formation. The most stable configuration assumes P 3 symmetry, and its lattice consists of one-dimensional H 2 ··· hydrogenic chains. Symmetrization of these chains results in the formation of helices, which are reminiscent of the trigonal phase of sulfur. The R 3 m - phase, which is comprised of these helices, becomes dynamically stable by 250 GPa and has a high density of states at the Fermi level. We explore the geometric relationships between R 3 m - and the Im3 m - and Imm 2-H 6 structures found in prior investigations.