Reversible Os–Os bond breaking in the high nuclearity carbido-dianion [Os 10 C(CO) 24 ] 2– on reaction with halogens; X -ray structure analysis of [(Ph 3 P) 2 N][Os 10 C(CO) 24 I] and Os 10 C(CO) 24 I 2

The carbido-dianion [Os10C(CO)24]2– reacts with halogens (X2) to give first [Os10C(CO)24X]– and then Os10C(CO)24X2(X = CL,Br,I) and these clusters regenerate the dianion on treatment with nucleophilic reagents such as X–, PR3 or C5H5N; X-ray analysis of [(Ph3P)2N]-[Os10C(CO)24I] and Os10C(CO)24I2 shows that the reactions break Os–Os bonds on the metal surface giving ‘butterfly’ indentations bridged by I atoms.