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Hexanuclear Niobium Cluster Compounds with Protonated NâBase Cations
Octahedral clusters of the [M6X12] 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 [Nb6Cl18]2â, and in one case [Nb6Cl18]3â, anion and protonated Nâbase cations ([MImâH]+, [nPr3NâH]+, [TMGuâH]+, and [TznâH]+). They all are prepared using water scavenger compounds [SOCl2 or (Ac)2O] under oxidising conditions, resulting in twoâelectron (or oneâelectron, respectively) oxidized cluster units with respect to the starting material [Nb6Cl14(H2O)4]·4H2O. Of five members of this group singleâcrystal Xâray structures were determined. The cluster anions exist in all structures as discrete units. The acidic H atoms of all Nâbases are hydrogen bonded to H acceptors, in 4 cases to outer, exo bonded Cl atoms of the cluster unit and in one case to the O atom of a coâcrystallized THF molecule. In [TMGuâH]2[Nb6Cl18] chains of cluster anions exist hydrogenâbonded through bridging [TMGuâH]+ cations. ESI mass spectra of [MImâH]2[Nb6Cl18]·2SOCl2 and [TMGuâH]2[Nb6Cl18] show the expected isotopic distribution patterns for the anions together with other peaks associated to chloride mass losses and/or reduction processes