Stav dette: TERMINAL SUBSTITUTION AND CAGE INCORPORATION OF AN ETA-CYCLOPENTADIENYL RING INTO BORANE CAGE STRUCTURES - CRYSTAL-STRUCTURES OF [MO(ETA-C5H5)(ETA-5 ETA-1-C5H4)B4H7] AND [MO(ETA-C5H5)(ETA-3 ETA-2-C3H3)C2B9H9]