Hexanuclear Niobium Cluster Compounds with Protonated N-Base 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](2-), and in one case [Nb6Cl18](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 [SOCl2 or (Ac)(2)O] under oxidising conditions, resulting in two-electron (or one-electron, respectively) oxidized cluster units with respect to the starting material [Nb6Cl14(H2O)(4)]center dot 4H(2)O. Of five members of this group single-crystal X-ray structures were determined. The cluster anions exist in all structures as discrete units. The acidic H atoms of all N-bases 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 co-crystallized THF molecule. In [TMGu-H](2)[Nb6Cl18] chains of cluster anions exist hydrogen-bonded through bridging [TMGu-H](+) cations. ESI mass spectra of [MIm-H](2)[Nb6Cl18]center dot 2SOCl(2) and [TMGu-H](2)[Nb6Cl18] show the expected isotopic distribution patterns for the anions together with other peaks associated to chloride mass losses and/or reduction processes.