Comment on "The ligand polyhedral model approach to the mechanism of complete carbonyl exchange in [Rh4(CO)12] and [Rh6(CO)16]" by Brian F. G. Johnson, Dalton Transactions, 2015, 44, DOI: 10.1039/C4DT03360D.

Experimental results (recent IR, DFT calculations and modern multinuclear NMR measurements on Rh-containing clusters, together with earlier VT multinuclear NMR measurements) show that the use of the Ligand Polyhedral Model (LPM) to provide a general mechanism for ligand fluxionality in Transition Metal Carbonyl Clusters (TMCCs) in solution cannot be sustained; instead there are numerous examples of only partial CO-migration over either part or sometimes the whole of the Rh-polyhedron as well as rhodium and carbonyl polyhedral rearrangements of Rh9- and Rh10-TMCCs containing an interstitial P when, in the high temperature limiting spectra, all the metals and all the carbonyls become equivalent and show time-averaged values of (1)J(Rh-P) and (2)J(P-CO) respectively.

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