Improved access through ball milling: Octahedral Ta₆ cluster alkoxides with weakly coordinating cations and a rare example of an electron‐poor Ta₆ cluster

Abstract

From the reaction of activated (ball‐milled) [Ta6I14] with Mg‐methanolate or ethanolate the first examples of compounds with hexanuclear Ta6 units which have the octahedral edges bridged by alcoholato ligands are obtained. Either methanolato or iodido ligands are further attached to the exo sites of the Ta6 octahedra. The [Ta6(OCH3)i12(OCH3)a6]2− and [Ta6(OCH3)i12Ia6]2−/1− units were crystallized with large cations. Single crystal X‐ray diffraction studies have revealed the structures of four of these compounds. They show that the Ta−Ta atom distances are shorter than those found in comparable Ta6 halides, because of the much less pronounced matrix effect of the smaller O atoms compared to i. e. Cl. The cluster unit in (PPN)[Ta6(OC2H5)i12Ia6] comprises a rare example of an electron‐poor ensemble with 13 cluster based electrons (located in highest in energy, metal based orbitals). Differences of bond lengths between the clusters with 13 CBEs and 14 CBEs are in line with published theoretical descriptions of the bonding situation.

Alcoholate and Mixed Alcoholate/Iodide Supported Hexanuclear Niobium Cluster Compounds with a Mixed Face-Bridged/Edge-Bridged Cluster Pair Example

“…They all are found within the expected ranges. Very similar compounds to 2 and 3 exist in the Ta analogues, (Ph 4 P) 2 [Ta 6 (OC 2 H 5 ) 12 I 6 ] and (PPN) 2 [Ta 6 (OC 2 H 5 ) 12 I 6 ] [47]. The last one is in fact isostructural to 3, whereas compound 2 differs from the Ta analogue by the existence of a co-crystallized ethanol molecule and thereby by a different lattice.…”

“…The first step of the formation of the three title cluster compounds is the excision of [Nb 6 I 11 ] into anhydrous alcohols (for 1 methanol, for 2 and 3 ethanol). Ball milling of the precursor has been proven to be beneficial for the reactivity of the starting material [47]. In all three cases magnesium powder is added to the filtered solutions in large molar excess.…”

“…All three compounds consist of discrete cluster anions of the general formula [Nb 6 (OR) i 12 Y a 6 ] 2− (R = CH 3 or C 2 H 5 , Y a = OCH 3 or I) and the charge-compensated cations PPh 4 + , PPN + or the cluster cation [Nb 6 I i 8 (HOCH 3 ) a 6 ] 2+ . They represent further examples of electron-poor M 6 cluster alcoholates, of which two compounds for M = Nb and four for M = Ta have been published before [20,47]. The six outer coordination sites of the metal octahedra are occupied by methanolato ligands in 1 and iodido ligands in 2 and 3.…”

“…were synthesized [20], and in 2021 the Ta 6 alcoholates, [Mg(HOCH 3 ) 6 ][Ta 6 (OCH 3 ) 18 ]•6CH 3 OH and A n [Ta 6 (OC 2 H 5 ) 12 I 6 ] (A = PPh 4 , PPN; n = 1, 2) [47].…”

Hexanuclear Niobium Cluster Alcoholates – First Representatives with Isopropanolato Ligands

“…[39] The substitution of halide (Cl and I) by alcoholate anions requires strong Brønsted basic conditions, which are achieved by Mg(OR) 2 (R = CH 3 , C 2 H 5 ) for 1 and 2 or Li(OC 3 H 7 ) solutions for 3 and 4. [26][27] Under these conditions Nb 6 cluster units are easily oxidized and decompose such that strict anaerobic conditions are required. Nevertheless, the yields do not exceed ~59 %.…”