Metallocarbohedrenes as a class of stable neutral clusters: formation mechanism of M8C12 (M = titanium and vanadium)

Abstract

Evidence for the existence of metallocarbohedrenes [MacI2 (M = Ti and V)] as a general class of stable neutral molecular clusters is reported. Studies of the formation and growth of metal-carbon clusters M,C, reveal the general mechanisms responsible for the formation of the prominent cagelike structure, M6C12, using a laser-based timeof-flight mass spectrometer. Investigation of the effect of the ionizing laser fluence over at least 4 orders of magnitude and studies at 1064, 532, 355, and 266 nm establish that the prominence of the M6CI2 cluster arises due to its presence as a neutral rather than as the photofragment of clusters of large size. The unusual stability of this species for both Ti and V is consistent with the proposed cagelike structure being a pentagonal dodecahedron (point group symmetry Th).

Collision-Induced Dissociation of Vanadium−Carbon Cluster Cations

“…The reason for the dominance of metal loss is evidently the strong carbon-carbon bonding in the completed cage structure. 3,37 It should be noted that these fragmentation patterns are quite similar to those observed for the met-car Ti 8 C 12 + . 28 A detailed study of the primary CID patterns of the met-car V 8 C 12 + enabled a determination of the approximate dissociation threshold.…”

“…The present results provide further evidence for the met-cars being comprised of some stable C 2 units, which in turn is consistent with a structure such as the one we originally proposed. [1][2][3]31 Collision-induced dissociation experiments on V 8 C 13 + are also of interest since they could provide some insight into whether the extra carbon attributed to the very stable V 8 C 12 + molecule is either outside or inside the cage. As shown in Table 1, we observe that V 8 C 13 + does indeed behave like V 8 C 12 + by losing a neutral vanadium atom to become V 7 C 13 + as a primary fragmentation product.…”

Peculiar Structures of Small Magnesium Carbide Clusters: MgC2, (MgC2)2, and (MgC2)4

“…Similar coordination possibilities for C 2 2-have been suggested to occur in the new class of species known as Met-Cars that have the formula M 8 C 12 (M ) Ti, V, Zr, Hf, Fe, Cr, and Mo). [2][3][4][5][6] Specifically, Castleman et al [2][3][4] proposed a pentagonal dodecahedral cage structure for the Met-Cars in which each of the pentagonal faces contains three C atoms and two M atoms. Both to extend our earlier work on threedimensional clusters containing Mg atoms and to further examine cases where C 2 2-coordinates in both 1-and 2-fold ways, we decided to study the title cluster compounds.…”

Reactivities of Metallocarbohedrenes: Nb8C12+

“…Thus, the Nb 8 C 12 (Br) 5 + product grows in very slowly compared to the rate in which Nb 8 C 12 (Br) 4 + grows in. As shown in Figure 11, Nb 8 C 12 (I) 3 (H 2 O) + and Nb 8 C 12 (I) 4 + are produced quickly from CH 3 I in the pressure of a trace amount of background water, but they are converted into Nb 8 C 12 -(I) 4 (H 2 O) + and Nb 8 C 12 (I) 5 + very slowly. Even though the reaction time is quite long, 14 s, the Nb 8 C 12 (I) 3 (H 2 O) + and Nb 8 C 12 (I) 4 + precursor ions remain abundant.…”

“…Since the report of their discovery by Castleman and co-workers in early 1992, metallocarbohedrenes, M 8 C 12 (M ) Ti, V, Zr, Hf, Cr, Mo, and Fe) [1][2][3][4][5][6][7][8] have been studied intensely. A pentagonal dodecahedron cage structure with T h symmetry was originally proposed by Castleman and co-workers, [1][2][3][4][5] and several additional structures have been proposed to account for the special stability of these species.…”