Germanium substitution into the Hexatungstate Lindqvist Anion: Synthesis, structure and reactivity of ( n Bu 4 N) 3 [( i PrO)GeW 5 O 18 ].

The alkoxido germanium-substituted tungstate (TBA)3[(iPrO)GeW5O18] (TBA)31 (TBA+ = nBu4N+) has been synthesised from (TBA)2[W6O19] by degradation of the hexatungstate with (TBA)OH followed by treatment with Ge(OiPr)4. The X-ray crystal structure of the solvate (TBA)31.CH2Cl2 enabled comparison of the heteroatom coordination environments in the [(iPrO)MW5O18]3– homologues (M = Ge, 1; Sn, 2; Ti, 3). This showed 1 to have the shortest M–OC (1.747 Å), M–OW(ax) (2.215 Å) and average M–OW(eq) (1.872 Å) bonds in these anions. 1H, 13C and 17O NMR spectra were consistent with the {(iPrO)GeW5} structure, and the 183W NMR spectrum contained peaks at 56.7 and –84.9 ppm for equatorial and axial tungsten sites respectively, while 𝜈(W=O) was observed at 948 cm–1 in the FTIR spectrum of 1. Protonolysis of the Ge–OiPr bond in (TBA)31 with MeOH was slower than the analogous reaction with [(iPrO)SnW5O18]3– 2, but clean conversion to (TBA)3[(MeO)GeW5O18] (TBA)34 was observed after warming. The X-ray crystal structure of (TBA)34 showed disorder of the smaller {GeOMe} moiety within the hexametalate, as was previously observed for [(MeO)SnW5O18]3– and [(MeO)TiW5O18]3–. DFT calculations on 1, 2, and 3 provided insight into their structural, electronic, and spectroscopic properties and were consistent with experimental data.