Table: superconductors_2
Columns: formula
notation
t_c_k
no_of_cu_o_planes_in_unit_cell
crystal_structure

Question: Which crystal structures has a Tc(K) of 110 and the number of Cu-O planes in the unit cell is 3?
SQL: SELECT "crystal_structure" FROM superconductors_2 WHERE "no_of_cu_o_planes_in_unit_cell" = 3 AND "t_c_k" = 110