title: The loss of CO from [Rh12(mu12-Sn)(CO)27]4-: synthesis, spectroscopic and structural characterization of the electron-deficient, icosahedral [Rh12(mu12-Sn)(CO)25]4- and [Rh12(mu12-Sn)(CO)26]4- tetra-anions.
abstract: Heating (80 degrees C) the electron-precise, Sn-centred, icosahedral cluster [Rh(12)Sn(CO)(27)](4-) under a nitrogen atmosphere affords in sequence the electron-deficient icosahedral [Rh(12)Sn(CO)(26)](4-) and [Rh(12)Sn(CO)(25)](4-) derivatives. The reaction is reversible in solution and the parent compound is quantitatively regenerated upon exposure to carbon monoxide. The reaction course has been unravelled via a combination of Band-target Entropy Minimization (BTEM) IR analysis and X-ray studies. While icosahedral clusters displaying electron counts formally exceeding 13 skeletal electron pairs (SEP) are known, [Rh(12)Sn(CO)(26)](4-) and [Rh(12)Sn(CO)(25)](4-) show for the first time that icosahedral clusters may also be stabilized with a deficiency of SEPs with respect to the requirement based on the cluster-borane analogy. In contrast to the behaviour of the electron-precise cluster [Rh(12)Sn(CO)(27)](4-), the electron-deficient cluster [Rh(12)Sn(CO)(25)](4-) undergoes reversible electrochemical reductions.
authors.affiliation: Dipartimento di Chimica Fisica ed Inorganica, Università di Bologna, Viale Risorgimento 4, 40136, Bologna, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Femoni
authors.forename: Maria Carmela
authors.initials: MC
authors.lastname: Iapalucci
authors.forename: Giuliano
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authors.lastname: Longoni
authors.forename: Cristina
authors.initials: C
authors.lastname: Tiozzo
authors.forename: Stefano
authors.initials: S
authors.lastname: Zacchini
authors.forename: Brian T
authors.initials: BT
authors.lastname: Heaton
authors.forename: Johnathan A
authors.initials: JA
authors.lastname: Iggo
authors.forename: Piero
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authors.lastname: Zanello
authors.forename: Serena
authors.initials: S
authors.lastname: Fedi
authors.forename: Marc V
authors.initials: MV
authors.lastname: Garland
authors.forename: Chuanzhao
authors.initials: C
authors.lastname: Li