The problems of detecting hydrides in metal carbonyl clusters by 1H NMR: the case study of [H4−nNi22(C2)4(CO)28(CdBr)2]n− (n = 2–4)

Abstract

The new tetra-acetylide carbonyl clusters [H(4-n)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](n-) (n = 2-4) have been prepared by reacting [Ni(10)C(2)(CO)(15)](2-) with a large excess of CdBr(2).xH(2)O and the molecular structure of the di-anion [H(2)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](2-) has been fully elucidated by means of X-ray crystallography. The corresponding [HNi(22)(C(2))(4)(CO)(28)(CdBr)(2)](3-) and [Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](4-) conjugated bases are quantitatively obtained upon dissolution of [H(2)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](2-) salts in more basic solvents such as acetonitrile and DMSO, respectively. The hydride nature of both [H(2)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](2-) and [HNi(22)(C(2))(4)(CO)(28)(CdBr)(2)](3-) has been directly proved by (1)H NMR spectroscopy. Their resonances are very broad under all experimental conditions and their chemical shift greatly depends on solvent as well as temperature. Observation of the hydride resonances in [H(4-n)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](n-) (n = 2, 3) makes these clusters a case study of the phenomena behind the loss of any NMR signal in higher-nuclearity metal carbonyl cluster anions (MCCA). In the attempt to obtain a better insight on this experimental spectroscopic behaviour, solutions of [NMe(4)](3)[HNi(22)(C(2))(4)(CO)(28)(CdBr)(2)] have been investigated by dynamic light scattering (DLS) at various concentrations. The DLS experiments point out the presence in solution of a distribution of particles with nominal hydrodynamic diameters enormously greater than those of the free cluster ions resulting, probably, from aggregation in solution. This could formally justify the observed NMR behaviour, even if the present observations are preliminary and their quantitative assessment requires further systematic studies on MCCA aggregation in solution.

Synthesis, Structures and Electrochemistry of New Carbonylnickel Octacarbide Clusters: The Distorting Action of Carbide Atoms in the Growth of Ni Cages and the First Example of the Inclusion of a Carbon Atom within a (Distorted) Ni Octahedral Cage

“…We herein report the first examples of (carbonyl)Ni octacarbide clusters {i.e., [H 5-n n-(n = 3-5), [Ni 36-y C 8 (CO) 34-y (MeCN) 3 (Cd 2 Cl 3 )] 3-(y = 0-2) and [H 7-n Ni 42+y C 8 (CO) 44+y (CdX)] n-(n = 6,7; X = Cl, Br, y = 0, 1)}, which -in contrast to the previously reported tetraacetylide species, [Ni 22 (C 2 ) 4 (CO) 28 Cl] 3-, [15] [H 4-n Ni 22 (C 2 ) 4 -(CO) 28 (CdCl) 2 ] n-(n = 2-4) [14] and [HNi 25 (C 2 ) 4 -(CO) 32 ]…”

“…Crystals n-(n = 2-4; X = Cl, Br), [14] [H 6-n Ni 30 C 4 (CO) 34 (CdX) 2 ] n-(n = 3-6; X = Cl, Br, I) [12] and [H 7-n Ni 32 C 4 (CO) 36 (CdX)] n-(n = 5-7; X = Cl, Br, I). [13] Only n-(n = 6, 7; y = 0, 1; see the next section).…”

“…Spectroelectrochemical studies of the first reduction shows that the original ν n-(n = 2-4), the synthesis and structures of which have previously been reported. [14] In thf solution the prominent form is [H 2 Ni 22 (C 2 ) 4 (CO) 28 (CdBr) 2 ] 2-, which, in dmf deprotonates and is converted into the tetraanion [Ni 22 -(C 2 ) 4 (CO) 28 (CdBr) 2 ] 4-(see Figure S4 in the Supporting Information). [14] Note that in this case the presence and number of hydride atoms was fully confirmed by 1 H NMR spectroscopy.…”

“…[16] So far, Ni acetylide MCCs containing one, two or four C 2 units are known. [14,15,17] This must be contrasted by the fact that carbon is very poorly soluble in bulk Ni, and only the metastable Ni 3 C phase is known, [18] which possesses a ccp structure.…”

“…[12][13][14][15] In particular, the species directly obtained by performing the reaction in thf is the dihydride trianion [H 2 n-(n = 3-6) [12] are formed. Conversely, by operating in acetone with a large excess of CdCl 2 ·2.5H 2 n-(n = 2-4) [14] is obtained. Thus, the reaction between [Ni 10 C 2 (CO) 15 ] 2-and CdCl 2 ·2.5H 2 O seems to be very sensitive to the experimental conditions, and it can result in three different products, depending on the stoichiometry and the reaction medium.…”