www.elsevier.nl/locate/jorganchem Journal of Organometallic Chemistry 593 – 594 (2000) 325 – 334 Synthesis and characterization of new paramagnetic nickel carbonyl clusters containing antimony atoms: X-ray structure of [NEt 3 CH 2 Ph] 2 [Ni 15 ( 12 -Sb)(CO) 24 ] and [NEt 4 ] 3 [Ni 10 Sb 2 ( 12 -Ni)(CO) 18 ] Vincenzo G. Albano a, *, Francesco Demartin b , Cristina Femoni c , Maria Carmela Iapalucci c , Giuliano Longoni c,1 , Magda Monari a , Piero Zanello d a Dipartimento di Chimica ‘G. Ciamician’, Uniersita ` di Bologna, ia F. Selmi 2, I -40126 Bologna, Italy b Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Uniersita ` di Milano, ia G. Venezian 21, I -20133 Milan, Italy c Dipartimento di Chimica Fisica ed Inorganica, Uniersita ` di Bologna, iale del Risorgimento 4, I -40136 Bologna, Italy d Dipartimento di Chimica, Uniersito ` di Siena, Pian dei Mantellini 44, I -53100 Siena, Italy Received 16 June 1999; accepted 7 September 1999 Dedicated to Professor Fausto Calderazzo on the occasion of his 70th birthday in recognition of his outstanding contributions to chemistry. Abstract The reaction of the [Ni 6 (CO) 12 ] 2 - dianion with SbCl 3 in a 2.5:1 molar ratio leads to formation of the new [Ni 15 ( 12 - Sb)(CO) 24 ] 2 - , 1 2 - , cluster with good selectivity. This has been conveniently separated from [Ni 9 (CO) 18 ] 2 - , [Ni 10 (SbNi(CO) 3 ) 2 ( 12 -Ni)(CO) 18 ] n - , 2 n - ,(n =2, 3) and other side-products by differential solubility of their [NEt 4 ] + salts and isolated in 50 – 60% yields. The corresponding [NEt 3 CH 2 Ph] 2 [1] salt was obtained from [NEt 4 ] 2 [1] by metathesis in acetonitrile with [NEt 3 CH 2 Ph]Cl and has been structurally characterized. The structure of 1 2 - consists of a distorted Sb-centered Ni 12 ( 12 -Sb) icosahedral moiety, capped by three Ni atoms on three adjacent triangular faces. The 1 2 - dianion is moderately stable to oxidation and has been electrochemically reduced to the corresponding tri-, tetra- and penta-anion; these electrogenerated species are stable only on the timescale of cyclic voltammetry. The 1 2 - dianion is readily degraded upon exposure to an atmosphere of carbon monoxide to a mixture of Ni(CO) 4 and a yet uncharacterized red – violet intermediate, which has been tentatively formulated as the [Ni 6 Sb(CO) x ] 2 - dianion on the basis of its spectroscopic features. The above mixture converts under nitrogen into the known 2 n - (n =3, 4), through the intermediate formation of the new [Ni 10 Sb 2 ( 12 -Ni)(CO) 18 ] n - , 3 n - ,(n =3, 4) species. Pure 3 3 - has been obtained by degradation of 2 3 - with two equivalents of triphenylphosphine by elimination of two equivalents of Ni(CO) 3 (PPh 3 ) and has been structurally characterized in its tetraethylammonium salt. The Ni-centered icosahedral 3 3 - trianion shows a chemical and electrochemical redox propensity comparable to that of the parent 2 3 - compound and is readily transformed in its corresponding 3 2 - and 3 4 - anions upon oxidation and reduction, respectively. Systematic observation of apparently exceptional electron counts and redox propensity by the above Ni-centered icosahedral clusters validate the previous attribution of these properties to the presence of interstitial nickel atoms and concomitant stabilization imparted by the peripheral antimony heteroatoms. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Carbonyl nickel cluster; Antimony; Crystal structure; Electrochemistry 1. Introduction A wide series of icosahedral nickel carbonyl clusters containing Group 14 – 16 elements has been synthesized [1–11]. As pictorially shown in Scheme 1, those display- ing C 5 symmetry can be divided in four sets: (a) non- centered [Ni 10 (ER) 2 (CO) 18 ] 2 - (E =P, As, Sb, Bi; R =alkyl or aryl substituent) [1–5], (b) E-centered [Ni 12 ( 12 -E)(CO) 22 ] 2 - (E =Ge, Sn) [8], (c) Ni-centered [Ni 10 E 2 ( 12 -Ni)(CO) 18 ] n - (E =Se, Bi; n =2–4) [6,11], and (d) Ni-centered [Ni 10 (ER) 2 ( 12 -Ni)(CO) 18 ] n - (E = * Corresponding author. 1 Also corresponding author. 0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S0022-328X(99)00523-9