Synthesis and characterization of novel types of adducts of nickel carbonyl clusters with indium halides: x-ray structures of [NEt4]3[Ni6(.mu.3-InBr3)(.eta.2-.mu.6-In2Br5)(CO)11].cntdot.Me2CO, [NEt4]4[Ni6(.eta.2-.mu.6-In2Br5)2(CO)10].cntdot.Me2CO, and [NEt4]4[Ni12(.mu.6-In)(.eta.2-.mu.6-In2Br4OH)(CO)22]