The compounds Ge₂ H₅Mn(CO)₅, Ge₂H₅Co(CO)₄ (Ge₂H₅)₂Fe(CO)₄, Ge₃H₇Mn(CO)₅, [GeH₂Mn(CO)₅] ₂ and [GeH₂Co(CO)₄] ₂ have been prepared by alkali-halide elimination reactions between the appropriate polygermanyl halides and metal carbonyl anions. The characterisation by infrared, Raman, n.m.r. and mass spectrometry of these compounds is discussed in detail. The physical properties and reactions have also been investigated and compared, in parallel with the parent polygermanes. Reagents used include hydrogen halides, group IV metal halides, mercuric halides and Na/NH₃ solution. Most of the reactions were studied by n.m.r. spectroscopy and the intermediates and products further characterised. Transition metal exchange is shown to be a useful synthetic route to yield the unsymmetric iron compound Ge₂H₅(GeH₃)Fe(CO)₄ and possibly GeH₃ (SiH₃)Fe(CO)₄. The polygermanyl-transition metal carbonyl derivatives are shown to be more stable than the germyl analogues and reasons, with spectroscopic evidence, are discussed.