Hexanuclear Niobium Cluster Compounds with Protonated N‐Base Cations

Abstract

Octahedral clusters of the [M 6 X 12 ] type offer numerous possibilities to form structural arrangements through different choices of bonding situations. In this paper a series of new cluster compounds of the transition metal niobium is described, which consist of the [Nb 6 Cl 18 ] 2-, and in one case [Nb 6 Cl 18 ] 3-, anion and protonated N-base cations ([MIm-H] + , [nPr 3 N-H] + , [TMGu-H] + , and [Tzn-H] +). They all are prepared using water scavenger compounds [SOCl 2 or (Ac) 2 O] under oxidising conditions, resulting in two-electron (or one-electron, respectively) oxidized cluster units with respect to the starting material [Nb 6 Cl 14 (H 2 O) 4 ]•4H 2 O. Of five members of this group single-crystal

Cluster Compounds with Oxidised, Hexanuclear [Nb6Cli12Ia6]n− Anions (n=2 or 3)

“…This successful concept of treating [Nb 6 Cl i 12 X a 2 (H 2 O) a 4 ] ⋅ 4H 2 O ( X =Cl or I) with a water scavenger acting as reactant, solvent and oxidiser, and supplying further ligands has been introduced before. [ 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ] All four investigated compounds are obtained in high yield. The experimental conditions for the synthesis of 1 to 4 are summarized in Scheme 1 .…”

“…Because of the presence of two distinct different coordination spheres, inner (i) and outer (a) in [M 6 X i 12 X a 6 ] type cluster compounds, we started to search for preparative procedures for mixed chloride-iodidesupported cluster complexes with only one halide type on each of the two different coordination site types, that is, cluster ) with a water scavenger acting as reactant, solvent and oxidiser, and supplying further ligands has been introduced before. [42][43][44][45][46][47][48][49][50] All four investigated compounds are obtained in high yield. The experimental conditions for the synthesis of 1 to 4 are summarized in Scheme 1.…”

Strong Cluster-Supported Brønsted Acids: Hexanuclear Niobium Cluster Compounds with Protonated Crown Ether Cations: (Crown-H)2[Nb6Cl12iX6a] (X = Cl or Br) and the Intermediate [Nb6Cl16(H2O)2]·4 dioxane

“…A comparison of the Nb–Cl a and the Nb–Br a distances in 1A – 1C and 2A and 2B with values found in literature of the 14 CBE cluster compounds also shows comparable values. One exemplarily selected example for Nb–Cl a distances in the 14 CBE cluster units is the value of 2.4886 Å found in [(TMGu)­H] 2 [Nb 6 Cl 18 ] ((TMGu)­H: tetramethyl guanidinium) . A recently published study has shown that the M – X a are influenced in the range of ±0.03 Å by the hydrogen bond originating from the X a atoms .…”

“…This compound forms just on adding the desiccant SOCl 2 to a suspension of [Nb 6 Cl 14 (H 2 O) 4 ]·4H 2 O in a dioxane/petrol ether mixture. Contrary to very similar reaction mixtures but different solvents, complete removal of the water ligands does not happen. ,, Presumably, compound 3 is an intermediate of the multi-step dehydration of the water-containing starting material, which crystallizes in small amounts from the given solvents. In other solvents, the reaction sequence proceeds and compounds with the [Nb 6 Cl 18 ] 2– unit form.…”

“…Generally, for all classes of salts, the existence of the corresponding Brønsted acid is a very advantageous prerequisite for the generation of other salts of the respective anion. In 2020, we reported about hexanuclear niobium cluster salts with protonated and thereby acidic N-bases . For the heavier group VB analogue tantalum, the cluster acid H 2 [Ta 6 Cl 18 ]·6 H 2 O has been published before, unfortunately without information about the positions of the oxygen atoms .…”