Platinum chemical shifts

A more quantitative attempt at interpreting platinum chemical shifts requires that we consider some form of the Ramsey (48) equation, which describes the resonance frequency, v9 in terms of the paramagnetic screening term, o>- QAB is a charge-density, bond-order matrix, AE is the average excitation energy, and r represents a distance from the nucleus for, in this case, a given d electron. 

Most of the reported results are given as evidence for structures in solution of compounds whose crystal structures are known from X-ray data. Some of them are completed by and P NMR spectra. We will give only the NMR parameters of these compounds using the chemical formulae. For more structural details, the reader can refer to the original publications. Platinum chemical shifts are referred to S = 21.4 MHz. In [Pt2Fe(dppm)2(CO)4], 5( Pt) = + 790 for the platinum atom bound to one phosphorus atom, and (i95pt)=+497 for the platinum bound to two phosphorus atoms, V(i 5pt,i95pt)= 1730 Hz [100]. Other results are presented in Table 20. 

Phosphorus-31—tritrium couplings see Tritium—phosphorus-31 couplings Platinum chemical shift, 452 Platinum-195 NMR, 3,8,101,446,452 Platinum-195—tin-119 couplings see Tin-119—platinum-195 couplings Polarization transfer see Cross polarization and INEPT Polyamides, chemical shift, 237-38 Polyelectrolyte, 325 Poly-L-glutamic acid, 147-48 Polymers, glassy, 365 Polymorphism, 371-72... 

More than a decade ago, Hamond and Winograd used XPS for the study of UPD Ag and Cu on polycrystalline platinum electrodes [11,12]. This study revealed a clear correlation between the amount of UPD metal on the electrode surface after emersion and in the electrolyte under controlled potential before emersion. Thereby, it was demonstrated that ex situ measurements on electrode surfaces provide relevant information about the electrochemical interface, (see Section 2.7). In view of the importance of UPD for electrocatalysis and metal deposition [132,133], knowledge of the oxidation state of the adatom in terms of chemical shifts, of the influence of the adatom on local work functions and knowledge of the distribution of electronic states in the valence band is highly desirable. The results of XPS and UPS studies on UPD metal layers will be discussed in the following chapter. Finally the poisoning effect of UPD on the H2 evolution reaction will be briefly mentioned. 

Platinum-195 is the only magnetically active isotope of platinum, the natural abundance being 33.8%. The shift of a saturated solution of K2PtCl6 is in D20 defined as zero ppm. The total chemical shift range is huge, about 13,000 ppm (from -6000 to +7000 ppm ). 

In the light of what we have said above, we might expect that satellites due to platinum-element coupling would be useful in structure determination. However, because of chemical shift anisotropy they are in fact often not visible, and experience (and theory) suggest that the chance of seeing them decreases as the magnetic field of the spectrometer increases. 

For platinum(O) complexes, [42] analysis of the 1H chemical shifts and coupling constants as well as results of ID selective ROE experiments has allowed determination of the torsional angles j/ and

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If either one of the terms dominates, it is sometimes possible to observe correlations. For example, a linear dependence of 195Pt chemical shift with UV-visi-ble data for a series of octahedral platinum complexes has been identified [16]. 

Metal chemical shifts have not found extensive use in relation to structural problems in catalysis. This is partially due to the relatively poor sensitivity of many (but not all) spin 1=1/2 metals. The most interesting exception concerns Pt, which is 33.7% abundant and possesses a relatively large magnetic moment. Platinum chemistry often serves as a model for the catalytically more useful palladium. Additionally, Pt NMR, has been used in connection with the hydrosilyla-tion and hydroformylation reactions. In the former area, Roy and Taylor [82] have prepared the catalysts Pt(SiCl2Me)2(l,5-COD) and [Pt()i-Cl)(SiCl2Me)(q -l,5-COD)]2 and used Pt methods (plus Si and NMR) to characterize these and related compounds. These represent the first stable alkene platinum silyl complexes and their reactions are thought to support the often-cited Chalk-Harrod hydrosilylation mechanism. 

Recent applications of X/Y correlation techniques to measure chemical shifts of low- , spin-1/2 transition metal nuclei other than rhodium focused mainly on the analysis of silver and tungsten complexes in addition, the use of 13C-relayed H/195Pt correlations for the stereochemical analysis of some platinum complexes was explored.44 A report on the application of 31P/51V correlation spectroscopy demonstrated further the possibility of indirect detection of rapidly relaxing quadrupolar metal nuclei and the feasibility of the... 

Because the chemical shifts of the nonexchangeable nucleobase proton signals are sensitive to (de)protonations of the aromatic structure, the absence of certain protonation shifts, or alterations in the expected pKa values, can give valuable information about the sites where platinum is bound. So, in N7-platinated guanine, no N7 protonation shift around pH 2 is observed, whereas the pKa of the N1 protonation decreases from 9.5 to 8.5 (54). 

Nitrite complexes can be simply prepared by metathetical replacement with nitrite ion.1163 The structure of n-anj-Pt(N02)2 P-(p-tol)3 2 has a Pt—N distance of 2.030(5) A and N—O distances of 1.228(8) A and 1.98(7) A.11 4 Chemical shift (5 Pt) and coupling constant data have been tabulated for a large group of platinum(II) and (IV) nitro complexes. Both chemical shift and coupling constant changes upon ligand substitution are dominated by the nature of the trans ligand/165... 

Two features need to be noted. Firstly, platinum-195 chemical shifts are quite sensitive to temperature, and in order to obtain acceptably narrow lines the solution temperature should be kept constant over the data accumulation time. Secondly, solvent effects need to be considered. A study of cis- and fraraj-PtCl2(PBu )2 in 14 solvents shows a change in A<5(P) of only 0.83p.p.m., but a change in Av(PtP) of 84.2Hz between n-hexane and acetonitrile.1355 Further work on temperature, solvent, substituent, oxidation state and stereochemical effects on 31P and 195Pt NMR chemical shifts and complexes is needed, and further efforts to collect and correlate data will be very useful.1356-1358... 

An acetylacetonate platinum(II) complex [PtMe3(acac)]2 is one of the few complexes for which 195Pt chemical shift anisotropy has been measured in the solid state.1605... 

The H NMR spectra of the platinum complexes display characteristic high-field chemical shifts of the vinyl protons of the complexed olefin, at the range of <5 2.56-3.02... 

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