FULL PAPER DOI: 10.1002/ejic.201101386 Cage Rearrangements in Dodecanuclear Co–Pt Dicarbido Clusters Promoted by Redox Reactions Cristina Femoni, [a] Maria Carmela Iapalucci, [a] Giuliano Longoni, [a] Stefano Zacchini,* [a] Serena Fedi, [b] and Fabrizia Fabrizi de Biani [b] Keywords: Cluster compounds / Carbonyl ligands / Structure elucidation / Electrochemistry / Carbides The chemical reduction of [Co 8 Pt 4 C 2 (CO) 24 ] 2– ([1] 2– ) with Na/ naphthalene results, after workup, in the isolation of either [Co 10 Pt 2 C 2 (CO) 22 ] 4– ([2] 4– ) or [Co 8 Pt 4 C 2 (CO) 20 ] 4– ([3] 4– ), de- pending on the experimental conditions. All these species undergo several chemical and/or electrochemical redox reac- tions, disclosing the existence of structurally related dodeca- nuclear clusters [1] n– (n = 0–4), [2] n– (n = 2–6) and [3] n– (n = 1–7). In the attempt to isolate more reduced species, 1. Introduction Dimetallic and heteronuclear Metal Carbonyl Clusters (MCCs) are interesting both as molecular species and as precursors of metal nanoparticles. In the latter case, the use of a dimetallic molecular precursor enables the preparation of dimetallic nanoparticles with well-defined composi- tions. [1–4] At the molecular level, the synergic effect of two metals with complementary properties and/or the stabilis- ing effect of an interstitial heteroelement results in larger and more stable molecular MCCs. [5,6] Indeed, the largest homoleptic MCC reported to date is the dimetallic cluster [Ni 32 Pt 24 (CO) 56 ] 6– . [7] In addition, homometallic Ni MCCs are limited to a nuclearity of 12, but this can be increased to 42 by including interstitial carbide atoms. [8] The increased stability of dimetallic and heteronuclear molecular MCCs may result in the appearance of peculiar chemical and physical properties, such as multivalence and paramagnetism. [9] This has been recently exemplified by the Co–Pt dicarbides [Co 8 Pt 4 C 2 (CO) 24 ] n– ([1] n– )(n = 1–4) which display both multivalency (i.e. they undergo several redox- reversible processes) and paramagnetism in the odd-elec- tron monoanion and the even-electron dianion. [10] Herein, we report on the chemical reduction of [1] 2– , which results in either [Co 10 Pt 2 C 2 (CO) 22 ] 4– ([2] 4– ) or [Co 8 Pt 4 C 2 (CO) 20 ] 4– ([3] 4– ), depending on the experimental conditions. Both spe- [a] Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy Fax: +39-051-2093690 E-mail: stefano.zacchini@unibo.it [b] Dipartimento di Chimica, Università di Siena, Via De Gasperi 2, 53100 Siena, Italy Eur. J. Inorg. Chem. 2012, 2243–2250 © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2243 [1] n– ,[2] n– and [3] n– undergo structural rearrangements re- sulting, among others, in the formation of the new species [Co 10–x Pt 2+x C 2 (CO) 24 ] 2– ([4] 2– )(x = 0–2) structurally related to [1] 2– . These dodecanuclear M 12 C 2 dicarbido clusters are not isostructural and differ in the metal composition and/or the number of CO ligands. Nevertheless, they can be readily in- terconverted even if the interconversion reactions are not straightforward. cies have been characterised by chemical, spectroscopic and structural methods. Electrochemical studies show that both species undergo several redox changes, some of which show features of chemical reversibility on the cyclovoltammetric time scale. Although [1] 2– ,[2] 4– and [3] 4– are all dodecanu- clear M 12 E 2 species, they display different metal geometries but can be readily interconverted. 2. Results and Discussion 2.1 Synthesis of [Co 10 Pt 2 C 2 (CO) 22 ] 4– ([2] 4– ), [Co 8 Pt 4 C 2 (CO) 20 ] 4– ([3] 4– ) and [Co 10–x Pt 2+x C 2 (CO) 24 ] 2– ([4] 2– ) It has been previously reported that [Co 8 Pt 4 C 2 (CO) 24 ] 2– ([1] 2– ) can be chemically or electrochemically oxidised to [1] – , as well as reduced to the trianion [1] 3– and the tetra- anion [1] 4– . Both, [1] 2– and [1] – have been isolated and struc- turally characterised. [10] In an attempt to isolate [1] 3– and [1] 4– by chemical reduction of [1] 2– with Na/naphthalene, the new species [Co 10 Pt 2 C 2 (CO) 22 ] 4– ([2] 4– ) and [Co 8 Pt 4 C 2 - (CO) 20 ] 4– ([3] 4– ) have been obtained. As summarised in Scheme 1, isolation of either [2] 4– or [3] 4– only depends on the workup procedure adopted after reduction of [1] 2– . To demonstrate this point, [1] 2– was reduced to [1] n– (n = 3–4), and the resulting suspension was divided into two portions. One portion was treated according to procedure (A) and the second according to procedure (B) resulting in the isola- tion of [2] 4– and [3] 4– , respectively. Conversely, reduction of [1] 2– under CO resulted in complete decomposition, [Co(CO) 4 ] – being the only detectable carbonyl product.