Soft routes to inorganic frameworks via assembly of molecular building blocks

Metallic oxides--Synthesis;Polyoxometalates;Chemical processes

Kandasamy, Balamurugan ; Bruce, Peter G. ; Bruce, Peter G.

University:University of St Andrews

Department:Chemistry (School of)

关键词: Metallic oxides--Synthesis;    Polyoxometalates;    Chemical processes;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/3120/BalamuruganKandasamyPhDThesis.pdf?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

The assembly of mononuclear and polynuclear molecular building blocks has beeninvestigated as a route to extended metal oxide structures. Various [MX[subscript(y)]]ⁿ⁻ (X = Cl,OMe, OH) and [(RO)M’M₅O₁₈]³⁻ (R = MeO, M’ = Sn, M = W) building blocks havebeen synthesised. Controlled hydrolysis has been explored for transition and maingroup metal hexahalides [MCl₆]ⁿ⁻ M=Ti, Sn using ¹⁷O enriched water.An attempted synthesis of [Me₃NCH₂Ph] [Sn(OMe)₆] gave the dinuclear product[Me₃NCH₂Ph] [Sn₂(OMe)₉]. Variable temperature ¹H NMR studies revealed exchangebetween terminal and bridging alkoxides and the limiting spectrum is consistent withsolid state structure. 2,6-lutidinium hydrochloride was synthesised and used tochlorinate the metal alkoxides {M(OR)[subscript(n)]} (M = Nb). A route to monochloro niobiumalkoxide {NbCl(OMe)₄} was developed and variable temperature¹H NMRspectroscopy studies of {NbCl(OMe)₄} in different solvents revealed exchangebetween bridging and terminal alkoxides and also suggested the presence of differentstructural isomers in solution.A novel heterometallic Lindqvist type of POM containing Sn has been successfullysynthesised by using controlled hydrolytic aggregation. A mixture of (TBA)₂WO₄,WO(OMe)₄ and {Sn(O[superscript(t)] Bu)₄} was partially hydrolysed in a non-aqueous solvent togive (TBA)₃[(MeO)SnW₅O₁₈] (1).¹¹⁹Sn NMR INEPT and selective tin decoupledproton NMR experiments have been carried out to determine the axial and equatorial²J {¹¹⁹Sn*¹⁸³W} coupling constants and to estimate³J{¹¹⁹Sn¹H} and ³J{¹¹⁷Sn¹H}coupling constants. The electrochemistry of (1) was studied by cyclic voltammetry(CV), and was shown to undergo a reversible one electron reduction close to thesolvent limit.Hydrolysis of [(MeO)SnW₅O₁₈]³⁻produced [(OH)SnW₅O₁₈]³⁻(2) which is stable in thesolid state but in solution undergoes a condensation reaction to give [(µ-O)(SnW₅O₁₈)₂]⁶⁻(3).The chloro stannotungstate [ClSnW₅O₁₈]³⁻ (4)was also obtained during the synthesis of (1)and (2). Compounds (2) and (4) are crystallographically isostructural and Sn hetero site wasdisordered over all six metal positions in both anions. The redox properties of (4) werestudied by CV and showed an irreversible reduction peak at -1.67 V. Compound (4) is stable in air and did not react with H₂O or PhOH but did react with MeOH or NaOMeto give (1). It also reacted with diisopropylamine (DIPA) to produce the H-bondedaggregate [(Prⁱ₂NH₂)₂(µ-O)(SnW₅O₁₈)₂]⁴⁻. The adduct structure is related to a recentlycharacterised titanium analogue [(µ-O)(TiW₅O₁₈H)₂]⁴⁻, which forms the H-bondedTHF adduct [(µ-O)(TiW₅O₁₈H)₂(THF)]⁴⁻.2D-¹H EXSY NMR studies of the mixtures of (1) and MeOH did not show anyexchange peaks between (1) and methanol which demonstrates that exchange is slowbut reactivity studies of (1) have been carried out with various alcohols and phenols togive substituted products. Sterically smaller alkyl groups gave trans disorderedstructures, but no disorder is present in structures of anion with bulkier aliphaticalkoxide and aryloxide groups. Hydrogen bonding was observed between the POMcage and pendant phenolic OH groups All the alkyl and aryloxido derivatives havebeen characterised by single crystal X-Ray diffraction,¹H and multinuclear NMRspectroscopy, infrared spectroscopy and CHN analysis.Preliminary studies to explore the immobilisation of metal alkoxides [Ti(OPrⁱ )₄] and (1)on ~30% OH functionalised Si(111) surfaces have been carried out. The attemptedcovalent immobilisation of (1) to Si(111) surfaces appeared to be successful fromAtomic Force Microscopy (AFM) measurements.