期刊
INORGANICS
卷 10, 期 8, 页码 -出版社
MDPI
DOI: 10.3390/inorganics10080107
关键词
germanium; fluoride; cations; crystal structures
资金
- CASE studentship
- GE Healthcare
- EPSRC [EP/R513325/1, EP/N035437/1, EP/N509747/1]
- EPSRC Mithras Programme [EP/S032789/1]
In this study, a series of complexes containing trifluorogermanium cations were characterized by reaction analysis and spectroscopy techniques, and the isomerization phenomenon in solution was reported. Dicationic complexes containing the GeF22+ fragment were synthesized using different ligands and reaction conditions, and their structures were investigated. In addition, the effect of sequentially removing fluoride atoms from a complex on the bonding was studied using density functional theory calculations.
The reaction of [GeF4L2], L = dmso (Me2SO), dmf (Me2NCHO), py (pyridine), pyNO (pyridine-N-oxide), OPPh3, OPMe3, with Me3SiO3SCF3 (TMSOTf) and monodentate ligands, L, in a 1:1:1 molar ratio in anhydrous CH2Cl2 formed the monocations [GeF3L3][OTf]. These rare trifluoro-germanium (IV) cations were characterised by microanalysis, IR, H-1, F-19{H-1} and, where appropriate, P-31{H-1} NMR spectroscopy. The F-19{H-1} NMR data show that in CH3NO2 solution the complexes exist as a mixture of mer and fac isomers, with the mer isomer invariably having the higher abundance. The X-ray structure of mer-[GeF3(OPPh3)(3)][OTf] is also reported. The attempts to remove a second fluoride using a further equivalent of TMSOTf and L were mostly unsuccessful, although a mixture of [GeF2(OAsPh3)(4)][OTf](2) and [GeF3(OAsPh3)(3)][OTf] was obtained using excess TMSOTf and OAsPh3. The reaction of [GeF4(MeCN)(2)] with TMSOTf in CH2Cl2 solution, followed by the addition of 2,2 ':6 ',2-terpyridine (terpy) formed mer-[GeF3(terpy)][OTf], whilst a similar reaction with 1,4,7-trimethyl-1,4,7-triazacyclononane (Me-3-tacn) in MeCN solution produced fac-[GeF3(Me-3-tacn)][OTf]. Dicationic complexes bearing the GeF22+ fragment were isolated using the tetra-aza macrocycles, 1,4,7,10-tetramethyl-1,4,7,10-tetra-azacyclododecane (Me-4-cyclen) and 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane (Me-4-cyclam), which reacted with [GeF4(MeCN)(2)] and two equivalents of TMSOTf to cleanly form the dicationic difluoride salts, cis-[GeF2(Me-4-cyclen)][OTf](2) and trans-[GeF2(Me-4-cyclam)][OTf](2). The F-19{H-1} NMR spectroscopy shows that in CH3NO2 solution there are four stereoisomers present for trans-[GeF2(Me-4-cyclam)][OTf](2), whereas the smaller ring-size of Me-4-cyclen accounts for the formation of only cis-[GeF2(Me-4-cyclen)][OTf], and is confirmed crystallographically. New spectroscopic data are also reported for [GeF4(L)(2)] (L = dmso, dmf and pyNO). Density functional theory calculations were used to probe the effect on the bonding as fluoride ligands were sequentially removed from the germanium centre in the OPMe3 complexes.
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