[Ta₆Cl₁₂(PrCN)₆][(Ta₆Cl₁₂)Cl₆]·2PrCN, A Compound with Homonuclear Mixed-Charge Cluster Units [Ta₆Cl₁₂]²⁺ and [Ta₆Cl₁₂]⁴⁺

Abstract

By partial oxidation of a solution of (Ta6Cl12)Cl2·6EtOH in butyronitrile, crystals of the title compound are obtained. The structure consists of mixed-oxidation state ions: [Ta6Cl12]2+ as cations [Ta6Cl12(PrCN)6]2+, and [Ta6Cl12]4+ as [(Ta6Cl12)Cl6]2- anions. Bond distances and IR spectra confirm the different oxidation states of the [Ta6Cl12] cluster cores.

Cation-anion pairs of niobium clusters of the type [Nb6Cl12(RCN)6][Nb6Cl18] (R=Et,nPr,iPr) with nitrile ligandsRCN forming stabilizing inter-ionic contacts

“…5 (left). This is exactly the same situation as in the literature-known Ta cluster complex [20] which is isostructural with 2. In 3 the environment of the iso-propyl nitrile ligands allow only for three independent contacts, see Fig.…”

“…Such disproportionation reactions are assumed to be accelerated by the presence of water, oxygen (air) or induced by elevated temperatures [22][23][24][25][26]. Whereas the tantalum cluster pair compound [Ta 6 Cl 12 ( n PrCN) 6 ][Ta 6 Cl 18 ] • 2( n PrCN) described in the literature was produced at elevated temperatures under air with a reaction time of more than 6 months in low yield, we assume that in the case of the reaction protocol for 1-3 the strong acidic reaction conditions lead to a quick oxidative degradation of clusters supplying the chloride ions needed for the formation of the title compounds much more quickly [20]. This assumption is supported by the fact that the anion [Nb 6 Cl 18 ] 2− comprises a cluster deprived of two electrons with respect to the starting material.…”

“…The cluster pair compound 1 crystallises in the monoclinic space group P2 1 /c while 2 and 3 crystallise in the triclinic space group P1 ̅ . [20]. Table 1 lists the crystallographic data of the title compounds and Table 2 presents average values and ranges of selected interatomic distances within the cluster units.…”

“…It is evident that in both structures layers of cluster cations are separated by layers of cluster anions. [20]) in both the b and c direction. Idealizing this cluster arrangements by assuming the presence of identical, neutral cluster units with same orientations, the structure of 1 could be derived from a cubic face-centred structure whereas 2 and 3 from a C-centered structure.…”

“…There is also an interesting, but so far very small group of Nb or Ta cluster compounds, which consist of two different cluster units within the same compound (cluster pairs). Reported Bu = C 4 H 9 ) has also been described [19][20][21].…”