New bimetallic Ni-Rh carbonyl clusters:: Synthesis and X-ray structure of the [Ni7Rh3(CO)18]3-, [Ni3Rh3(CO)13]3- and [NiRh8(CO)19]2- cluster anions

The reaction of the [Ni-6(CO)(12)](2-) dianion with [Rh(COD)Cl](2) (COD = cyclooctadiene) in acetone affords a mixture of bimetallic Ni-Rh clusters, mainly consisting of the new [Ni7Rh3(CO)(18)](3-) and [Ni8Rh(CO)(18)](3-) trianions. A study of the reactivity of [Ni7Rh3(CO)(18)](3-) led to isolation of the new [Ni3Rh3(CO)(13)](3-) and [NiRh8(CO)(19)](2-) anions. All these new bimetallic Ni-Rh carbonyl Clusters have been isolated in the solid state as tetrasubstituted ammonium salts and have been characterised by elemental analysis, X-ray diffraction studies, ESI-MS and electrochemistry. The unit cell of the [NEt4](3)[Ni7Rh3(CO)(18)] salt contains two orientationally-disordered v(2)-tetrahedral [Ni7Rh3(CO)(18)](3-) trianions with occupancy factors of 0.75 and 0.25. Besides, their inner Ni3Rh3 octahedral moieties Show two cus sites purely Occupied by Rh atoms, two tran's sites purely occupied by Ni atoms and the remaining two cis sites are disordered Ni and Rh sites with respective occupancy fraction of 0.5. At difference from the parent [Ni7Rh3 (CO)(18)](3-), the octahedral [Ni3Rh3(CO)(13)](3-) displays in ordered distribution of Ni and Rh atoms in two staggered triangles. The [NiRh8(CO)(19)](2-) dianion adopts an isomeric metal frame with respect to that of the [PtRh8(CO)(19)](2-) congener. As a fallout of this work, new high-yield Synthesis of the known [Ni6Rh3(CO)(17)](3-) and [Ni6Rh5(CO)(21)](3-) as well as other currently-investigated bimetallic Ni-Rh Clusters have been obtained.