Compounds with formula R2SrAl2O7 (R=rare earth) look superficially similar to the well-known bilayer manganites, but here the perovskite bilayers contain Al and are nonmagnetic. They efficiently separate the rare earth and Sr containing magnetic rock-salt layers. When R=Sm, these rock salt layers contain Sm and Sr in a 2:1 ratio, but because of their different sizes the Sm and Sr cations occupy different sites. The only magnetic ions, Sm3+, then form two, well separated, square 2D lattices lying on top of each other and nearest-neighbour antiferromagnetic interactions imply a magnetic structure which would result in a 2-in, 2-out structure, reminiscent of spin ice. Magnetic measurements do not show magnetic order down to 1.8 K, but the susceptibility indicates competing interactions. Muons can resolve the ground state in this and compounds with other R ions.