FULL PAPER DOI:10.1002/ejic.201402289 The Chemistry of Ni–Sb Carbonyl Clusters – Synthesis and Characterization of the [Ni 19 Sb 4 (CO) 26 ] 4– Tetraanion and the Viologen Salts of [Ni 13 Sb 2 (CO) 24 ] n– Carbonyl Clusters Cristina Femoni,* [a] Maria Carmela Iapalucci,* [a] Giuliano Longoni, [a] Stefano Zacchini, [a] Iacopo Ciabatti, [a] Raffaele Guido Della Valle, [a] Marcello Mazzani, [b] and Mauro Riccò [b] Keywords: Cluster compounds / Carbonyl ligands / Viologens / Nickel / Structure elucidation Within the reinvestigation of Ni–Sb carbonyl cluster chemis- try, we report here the synthesis and characterization of the new [Ni 19 Sb 4 (CO) 26 ] 4– cluster and the synthesis, structure, magnetic characterization and electrical resistivity of the viologen salts of the previously known [Ni 13 Sb 2 (CO) 24 ] n– (n = 2, 3) anionic species. The crystal structures of [NEt 4 ] 4 [Ni 19 Sb 4 (CO) 26 ], [EtV] 8 [Ni 13 Sb 2 (CO) 24 ] 3 ·4DMF·2C 6 H 14 and [EtV] 3 [Ni 13 Sb 2 (CO) 24 ]·1.5THF (EtV = 1,1'-diethyl-4,4'-bipyri- dilium cation, DMF = N,N-dimethylformamide, THF = tetra- hydrofuran) are described. Notably, the unit cell of [EtV] 8 [Ni 13 Sb 2 (CO) 24 ] 3 ·4DMF·2C 6 H 14 involves a mixture of two [Ni 13 Sb 2 (CO) 24 ] 3– trianions and one [Ni 13 Sb 2 (CO) 24 ] 2– di- anion, as it also contains eight [EtV] +· radical monocations, which are assembled in infinite stacks. In contrast, the unit cell of the [EtV] 3 [Ni 13 Sb 2 (CO) 24 ]·1.5THF salt contains four [Ni 13 Sb 2 (CO) 24 ] 3– trianions along with twelve [EtV] +· radical Introduction In the last few years, the chemistry of nickel carbonyl clusters containing from one to eight interstitial carbide atoms has been recognized as an enormous development. [1] Such a development fuelled a renewed interest in nickel clusters containing other main group elements as interstitial atoms, including the Ni–P (work in progress) and Ni–Sb carbonyl clusters. Notably, the presence of such elements within the metal lattice imparts extra stability to the whole structure; therefore, these clusters are likely to be stable in redox environments and could possibly give rise to multi- valent species. [2] Among the Ni–Sb compounds we have previously reported are the [Ni 10 {SbNi(CO) 3 } 2 (μ 12 -Ni)- [a] Department of Industrial Chemistry “Toso Montanari”, University of Bologna, Viale del Risorgimento 4, 40136 Bologna, Italy E-mail: cristina.femoni@unibo.it; maria.iapalucci@unibo.it http://www.chimica-industriale.unibo.it/it [b] Dipartimento di Fisica e Scienze della Terra, Università di Parma, Via Usberti 7/a, 43124 Parma, Italy Eur. J. Inorg. Chem. 2014, 4151–4158 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4151 monocations, four of which are arranged into two pairs of isolated dimers, whereas the other two sets of four form two infinite stacks that extend over the whole crystal. The charges of the miscellaneous ions have been assigned on the basis of electroneutrality and spectroscopic evidence. More specifically, the infrared spectra of [EtV] 8 [Ni 13 Sb 2 (CO) 24 ] 3 · 4DMF·2C 6 H 14 , both in the solid state and in solution, clearly indicate the presence of a 2:1 mixture of [Ni 13 Sb 2 (CO) 24 ] 3– and [Ni 13 Sb 2 (CO) 24 ] 2– anions. Resistivity measurements per- formed on pellets of powdered samples indicate that the [EtV] 8 [Ni 13 Sb 2 (CO) 24 ] 3 ·4DMF·2C 6 H 14 salt substantially be- haves as an insulator. A study of the magnetic behaviour of [EtV] 8 [Ni 13 Sb 2 (CO) 24 ] 3 ·4DMF·2C 6 H 14 evidences pairing among the electrons of the EtV +· molecules, in agreement with DFT calculations, and the odd-electron clusters behave as paramagnetic centres of spin S = 1. (CO) 24 ] n– (n = 2, 3), [3] [Ni 15 (μ 12 -Sb)(CO) 24 ] 2– , [Ni 10 Sb 2 (μ 12 - Ni)(CO) 18 ] 3–[4] and [Ni 31 Sb 4 (CO) 40 ] 6–[5] carbonyl clusters. After a further reinvestigation of this chemistry, we now report the synthesis and characterization of the new [Ni 19 Sb 4 (CO) 26 ] 4– species, as well as the physical and spec- troscopic characterization of the viologen salts of the [Ni 10 {SbNi(CO) 3 } 2 (μ 12 -Ni)(CO) 18 ] n– (n = 2, 3) clusters. Results and Discussion Synthesis and Characterization of [NBu 4 ] 4 [Ni 19 Sb 4 (CO) 26 ] The new brown [Ni 19 Sb 4 (CO) 26 ] 4– anionic cluster has been obtained from two different though related syntheses. The first synthesis was found when we were trying to obtain a hypothetical electron-poor Sb-centred icosahedral [Ni 12 (μ 12 -Sb)(CO) 19 ] 3– species, which would be isoelectronic with [Rh 12 (μ 12 -Sn)(CO) 25 ] 4– . [6] It had seemed reasonable that such a compound could have been obtained by degra- dation of the Sb-centred [Ni 15 Sb(CO) 24 ] 2– paramagnetic di-