The present invention describes novel organometallic compounds which are phosphorescence emitters. Such compounds can, as active constituents (functional materials), be used in a number of different applications, which in the broadest sense can be classed as belonging to the electronics industry. The compounds according to the invention are described by the formulas (I), (Ia), (II), (IIa), (III), (IIIa), (IV) and (IVa).