The syntheses of the first molecular meta-selenidomercurate(II), ortho-telluridothallate(III) and a hydrate of an ortho-selenidoplubate(IV) are presented alongside an improved and facile synthesis of the selenidobismuthate(III) with almost quantitative yields. By means of quantum chemical calculations, the energetics of the interconversions of small metalate anions is discussed and the existence of the heaviest homologues of [NO2]−, [NO3]−, [PO4]2− and [CO3]2− are predicted.