Transition Metals That Are Like Halides As we have seen,transition elements with 7 valence e (like Mn and Re)which are bonded to 2e donors (like CO) form dimers,because they need only one extra e. Another similarity is reactivity with light: Br2 hv→2Br Mnz(CO)o-hv2Mn(CO) Another similarity is a phenomenon called "coupling": Br+ Br-l co cO cO CO- Re, cO co co Mn(CO)5 Re(CO)5 CO XIV-7Transition Metals That Are Like Halides • As we have seen, transition elements with 7 valence e- (like Mn and Re) which are bonded to 2 e- donors (like CO) form dimers, because they need only one extra e- . • Another similarity is reactivity with light: Br2 2 Br Mn2(CO)10 2 Mn(CO)5 • Another similarity is a phenomenon called “coupling”: Br + I Br—I Mn(CO)5 + Re(CO)5 Mn Re CO CO CO CO CO CO CO CO CO CO hν hν XIV-7