31P MAS NMR spectroscopy

The second approach consists of synthesizing first the complex MLra 1(L X) with the desired ratio (L )/(M) this complex bears the reactive fragment X which then reacts with the surface of the silica. This method is of limited interest, because the synthesis and isolation of these functionalized complexes is not straightforward. One of the successful examples concerns the synthesis of nickel carbonyl complexes anchored to the surface via two bonds in an attempt to increase the stability through a sort of chelate effect. Initial attempts to achieve this by the methods described in Equation(5) (initial functionalization of silica) and Equation(6) (initial functionalization of complex) failed, as demonstrated by 29Si and 31P CP MAS NMR spectroscopies.51... 

Conclusions, some of them contrary to the above, were reached more recently by Zhuang et al. (145) from a combination of 31P and 1H MAS NMR spectroscopy of adsorbed trimethylphosphine. These authors found not only Lewis acid sites (vide infra), but also Brpnsted acid sites in TS-1 (145). They claimed that the 1H, 29Si MAS NMR spectra and the resonance related to Brpnsted acid sites in the 31P MAS NMR demonstrated clearly that the presence of Ti in the framework results in the formation of a new OH group, titanols, which is more acidic than the silanols of silicalite-1 (145) . The peak at 4.3 ppm in the 31P MAS NMR spectra was assigned to a ((CH3)3P-H)+ complex arising from the interaction of (CH3)3P with Brpnsted acid sites present on TS-1. The origin of this proton is not clear at present, especially because the MAS NMR spectra of the same TS-1 samples did not differ significantly from those of silicalite-1 (145) the latter, when free from impurities, is not known to be a Brpnsted acid. 

The ability of the boron atom of 59 to engage in a donor-acceptor interaction was illustrated with DMAP and DABCO (DABCO = diazabi-cyclo-[2.2.2]-octane) that readily formed the corresponding Lewis adducts. Interestingly, a similar behavior was retained after coordination of the phosphorus atom to palladium. The formation of the Lewis base adducts 66a and 66b of complex 65 (Scheme 38) was supported by solid-state 31P and nB CP/MAS-NMR spectroscopy (<5 1 B = 5-6 ppm), although the occurrence of decomposition and/or dissociation processes impeded spectroscopic characterization in solution and recrystallization to obtain X-ray quality crystals. Compounds 66a and 66b substantiate the ability of ambiphilic compounds to engage concomitantly into the coordination of donor and acceptor moieties. Such a dual behavior opens interesting perspectives for the preparation of metallo-polymers and multimetallic complexes. 

D MAS NMR techniques In the previous section, we reported applications of ID NMR spectroscopy, which enables the determination and quantitative characterisation of different phosphorus groups Q" via deconvolution of 31P resonances. Unfortunately, such an approach has at least two limitations. First, the 31P MAS NMR spectra suffer from broad and overlapping signals, and these methods fail when more complicated systems are to be analysed. Second, the structural information is significantly limited, for example the connectivities of Q group or through-space interactions cannot be established from only ID spectra. To overcome these limitations, it is necessary to apply more advanced 2D NMR techniques. 

Vinu and others219 exploited 31P CP/MAS NMR spectroscopy together with other instrumental techniques to describe physicochemical characterisation of a catalyst consisting of tungstophosphoric acid supported on zirconia and meso-porous silica MCM-41 and MCM-48. 

Characterisation of ZnAl204 powders was accomplished using 27A1 MAS-NMR spectroscopy.259 13C and 31P MAS-NMR spectra were used to study Zn(03PPh)(phen), Zn(03PR)2(phen) (R = Me, Et, Bz) and... 

The local structure of the fast solid ion-conductor Cu2P3I2, i.e. (CuI)8Pi2, was investigated by 1-D and 2-D 31P and 65Cu MAS-NMR spectroscopy.55131P NMR studies on SmFe4P12 show that the system remains in a paramagnetic state above the Curie temperature.552 The silica-supported complex =Si-ORh(P Pr3)2(H)2 was characterised by 31P MAS-NMR.553... 

Si 3H CP/MAS-NMR was used to probe interactions of transition metal carbonyl clusters (Ru3H(CO)M, Os2FI(CO)ii, Co(CO)4 ) deposited in the mesoporous aluminosilicate material MCM-41.637 A 29Si MAS-NMR study has been made of rhodium-amine complexes on Si02 surfaces.638 31P CP/MAS-NMR spectroscopy was able to characterise Cu6(TePh)6(PPh2Et)5 clusters in the pores of MCM-41.639... 

Information on the degree of disorder introduced by thermal treatment of hydroxyapatite during plasma spraying could be obtained by NMR spectroscopy. The positions and shift of 1H-MAS and 31P-MAS NMR peaks are indicative of the environment of the P043- tetrahedra in calcium orthophosphates and allow distinguishing between dehydroxylation (oxyhydroxyapatite) and decomposition (tricalcium phosphate, tetracalcium phosphate) products of hydroxyapatite. 

P and 19F NMR spectroscopy), and attempts to record a CP/MAS solid-state NMR spectrum (19F, 31P, 23Na) failed because of the large line-broadening by the 23Na ions (I = 3/2) and strong spin-spin coupling. 

Extensive characterisation studies have been performed with various techniques (XAFS, XPS, 31P CP/MAS-NMR, IR and Raman spectroscopies)13 to characterise Aul after deposition, and its decomposition and conversion into metal particles upon thermal treatment. The transformation of hydroxide supports into oxides was also followed. The amorphous hydroxides contain a larger number of surface hydroxyl groups and surface defects than do the corresponding oxides, and they interact more efficiently with Aul, which dissociates on the surface, releasing the... 

Very recently, Morais et al.178 presented the use of ID to 3D SS NMR spectroscopy in the studies of the structure of AlPO4-40 A1PO. From conducted MAS NMR experiments involving 31P and 27A1, it was apparent that the structure of the investigated AlPO4-40 contains at least four times more sites than expected. 

Figure 15.21. CP/MAS spectra l3C inp-dimethoxybenzene (note splitting induced in ortho carbons due to the asymmetry of the methoxy group), 29Si in poly-[dimethy lsiloxane) (PDMS), and 31P in bone mineral [roughly equivalent to Ca50H(P04)3]. (29Si spectrum reprinted with permission from Beshah K, Mark JE, Himstedt A, Ackerman JL. Characterization of PDMS model junctions and networks by solution and solid state silicon-29 NMR spectroscopy. J Polymer Sci B Polymer Phys. 1986 24 1207-1225. Copyright 1986 John Wiley Sons.)...

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