Searches for fundamental symmetry violations benefit from
large internal molecular fields, high polarizability, internal
co-magnetometry, and the ability to cycle photons - all of which can
be found in certain engineered polyatomic species. We discuss
experimental and theoretical developments in several linear metal
hydroxide (MOH) species, including spectroscopy, photon cycling, and
quantum control. We discuss how polyatomic structure gives rise to
unique capabilities, such as the existence of measurement schemes
which are sensitive to symmetry violations but insensitive to external
fields. We also discuss the cooling and spectroscopic measurements of
radium-containing polyatomic molecules, whose exotic nuclear features
give rise to further dramatic enhancements in sensitivity to symmetry
violations, using methods which should be applicable to a wide range
of molecules with exotic nuclei.