Bimetallic Nickel-Cobalt Hexacarbido Carbonyl Clusters [H 6-n Ni 22 Co 6 C 6 (CO) 36 ] n- (n =3-6) Possessing Polyhydride Nature and Their Base-Induced Degradation to the Monoacetylide [Ni 9 CoC 2 (CO) 16-x ] 3- (x = 0, 1) Iacopo Ciabatti, Cristina Femoni, Maria Carmela Iapalucci, Giuliano Longoni, and Stefano Zacchini* Dipartimento di Chimica Fisica e Inorganica, Universita ̀ di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy * S Supporting Information ABSTRACT: The reaction of [Ni 10 C 2 (CO) 16 ] 2- with Co 3 (μ 3 -CCl)(CO) 9 results in the new bimetallic Ni-Co hexacarbido carbonyl clusters [H 6-n Ni 22 Co 6 C 6 (CO) 36 ] n- (n =3-6), which possess polyhydride nature and can be interconverted by means of acid-base reactions. The tetra-anion [H 2 Ni 22 Co 6 C 6 (CO) 36 ] 4- and the hexa-anion [Ni 22 Co 6 C 6 (CO) 36 ] 6- have been isolated in a crystalline state and structurally characterized via X-ray crystallography. The six carbide atoms are lodged into Ni 7 CoC square antiprismatic cages. Addition of strong bases to [Ni 22 Co 6 C 6 (CO) 36 ] 6- affords mixtures of the monoacetylides [Ni 9 CoC 2 (CO) 16 ] 3- and [Ni 9 CoC 2 (CO) 15 ] 3- , which have been cocrystallized as [NEt 4 ] 3 [Ni 9 CoC 2 (CO) 16-x ](x = 0.58-0.84) salts, displaying tightly bonded interstitial C 2 units. 1. INTRODUCTION Several bimetallic Ni-Co carbide and acetylide carbonyl clusters are known, i.e., [Co 2 Ni 10 C(CO) 20 ] 2- , [Co 3 Ni 9 C- (CO) 20 ] 2- , 1 [Co 3 Ni 9 C(CO) 20 ] 3- , 2 [Co 3 Ni 7 C 2 (CO) 15 ] 3- , [Co 3 Ni 7 C 2 (CO) 16 ] n- (n = 2, 3), 3 and [Co 6 Ni 2 C 2 (CO) 16 ] 2- . 4 Their highest nuclearity is 12, and the Ni/Co ratio ranges from 0.33 to 5. The wide variability of the Ni/Co composition of these clusters is due to the fact that both metals form homometallic as well as carbido carbonyl clusters, and thus, several carbonyl precursors are available for the synthesis of bimetallic Ni-Co carbides via redox condensation. 5 Bimetallic carbonyl clusters are useful precursors for the preparation of metal nanoparticles with controlled composi- tion. 6-13 Thus, the possibility to prepare bimetallic Ni-Co molecular clusters with very different Ni/Co compositions makes these clusters quite attractive for the preparation of bimetallic magnetic Ni-Co nanoparticles, allowing a gradual variation of their properties. A fine control of the composition of the resulting bimetallic nanoparticles might result in a better understanding of the relationships existing between composi- tion and properties of the nanoparticles. In addition, bimetallic and heteronuclear clusters often display rather di fferent properties than the analogous homometallic species and can more easily reach higher nuclearities. This point makes bimetallic carbido carbonyl clusters attractive also from a molecular point of view. 14-18 Thus, we started a reinvestigation of Ni-Co carbide carbonyl clusters, aiming at obtaining higher nuclearity species. Herein, we report on the study of the reaction between [Ni 10 C 2 (CO) 16 ] 2- and Co 3 (μ 3 -CCl)(CO) 9 and the consequent isolation and structural characterization of the new hexacarbides [H 6-n Ni 22 Co 6 C 6 (CO) 36 ] n- (n =3-6), which represent more than twice an increase of the maximum nuclearity of Co-Ni-C clusters. Their reactions with strong bases, such as [NBu 4 ]- [OH], besides revealing the polyhydride nature of these clusters, a ff orded the new monoacetylide [Ni 9 CoC 2 (CO) 16-x ] 3- (x = 0, 1), structurally related to [Ni 10 C 2 (CO) 16 ] 2- . 2. RESULTS AND DISCUSSION 2.1. Synthesis of [H 6-n Ni 22 Co 6 C 6 (CO) 36 ] n- (n =3-6) and [Ni 9 CoC 2 (CO) 16-x ] 3- (x = 0, 1). The slow addition of an acetone solution of Co 3 (μ 3 -CCl)(CO) 9 to [Ni 10 (C 2 )(CO) 16 ] 2- dissolved in acetone results in the formation of a considerable amount of Ni(CO) 4 together with a new brown species, which has been isolated after removal of the solvent in vacuo, washing with water and toluene, and extraction of the residue in CH 3 CN. In this solvent, the new brown cluster displays ν(CO) at 2008(vs) and 1849(m) cm -1 . After layering n-hexane and di- isopropyl ether on the CH 3 CN solution, crystals suitable for X- ray analysis of [NEt 4 ] 4 [H 2 Ni 22 Co 6 C 6 (CO) 36 ] were obtained. The formation of [H 2 Ni 22 Co 6 C 6 (CO) 36 ] 4- is formally in agreement with eq 1: Received: May 15, 2012 Published: June 12, 2012 Article pubs.acs.org/Organometallics © 2012 American Chemical Society 4593 dx.doi.org/10.1021/om300412d | Organometallics 2012, 31, 4593-4600