Probing Isotope Shifts in ¹⁰³Rh and ¹⁹⁵Pt NMR Spectra with Density Functional Theory

Abstract

Zero-point vibrationally averaged (r g 0 ) structures were computed at the PBE0/SDD/6-31G* level for the [Pt

Isotope Effects in 195Pt NMR Spectroscopy: Unique 35/37Cl- and 16/18O-Resolved “Fingerprints” for All [PtCl6–n(OH)n]2– (n = 1–5) Anions in an Alkaline Solution and the Implications of the Trans Influence

“…Recent DFT computational studies aimed at understanding the possible origin of the experimental intrinsic isotope effects in the series of [PtCl 6– n (OH) n ] 2– ( n = 1–5) anions indeed show that the calculated Pt–Cl bond displacements trans to a hydroxido ligand are, on average, longer than those in the corresponding Pt–Cl distances trans to a coordinated water molecule in [PtCl 6– n (H 2 O) n ] (2– n )– ( n = 1–5) complexes. , This may be illustrated for geometry-optimized structures of the pair of complexes cis -[PtCl 4 (H 2 O) 2 ] and cis -[PtCl 4 (OH) 2 ] 2– . The computed Pt–Cl distance trans to a water molecule at 2.2778 Å in the former uncharged cis -[PtCl 4 (H 2 O) 2 ] species is considerably shorter than the corresponding bond in the cis -[PtCl 4 (OH) 2 ] 2– anion at 2.4124 Å, while the corresponding Pt–OH 2 and Pt–OH distances are 2.1424 and 2.0107 Å, respectively . For this pair of complexes, the mutually trans Cl–Pt–Cl bond distances in the cis -[PtCl 4 (H 2 O) 2 ] and cis -[PtCl 4 (OH) 2 ] 2– species are comparable at 2.3405 and 2.3741 Å, respectively.…”

“…In broad terms, therefore, these interesting, if subtle, differences in the intrinsic 1 Δ 195 Pt( 37/35 Cl) isotope effects observed in the [PtCl 6– n (OH) n ] 2– ( n = 1–5) anions, compared to their aquated (protonated) [PtCl 6– n (H 2 O) n ] (2– n )– ( n = 1–5) analogues, , can be understood in the context of the very high sensitivity of the σ( 195 Pt) nuclear shielding to extremely small differences in Pt–X (X = 35/37 Cl/OH/OH 2 ) bond displacements in their respective isotopologues (and when possible isotopomers), as previously predicted by the elegant theoretical work of Jameson et al − and in subsequent density functional theory (DFT) computational studies. ,− Generally, the intrinsic isotope shift for an NMR-active nucleus M bound to isotope X in a compound MX can be written as ΔM n ( m ′ / m X ) = σ M − σ M * = δ M * after the notation of Gombler and Jameson, where m and m ′ are the mass numbers of the light and heavy isotopes of element X, respectively, bound to M, with n indicating the number of chemical bonds separating atoms M and X, and σ M and δ M represent the magnetic shielding and chemical shift of nucleus M, with the asterisk indicating the quantities pertaining to the heavier isotope. It follows from the above definition that isotope shifts are usually negative ; i.e., the heavier isotope usually induces greater shielding or negative chemical shift change (after the sign convention proposed by Gombler and Wasylishen et al).…”

“…Given the extremely high sensitivity of the DFT-computed 195 Pt shielding to very small changes in the Pt–Cl bond displacements, typically ∼ 18300 ppm/Å in the gas phase for [PtCl 6– n Br n ] 2– anions, it is reasonable to expect that minute changes in the Pt–Cl bond displacements on the order of femtometers can result in detectable changes in the 195 Pt shielding of these complexes . Recent DFT computational studies aimed at understanding the possible origin of the experimental intrinsic isotope effects in the series of [PtCl 6– n (OH) n ] 2– ( n = 1–5) anions indeed show that the calculated Pt–Cl bond displacements trans to a hydroxido ligand are, on average, longer than those in the corresponding Pt–Cl distances trans to a coordinated water molecule in [PtCl 6– n (H 2 O) n ] (2– n )– ( n = 1–5) complexes. , This may be illustrated for geometry-optimized structures of the pair of complexes cis -[PtCl 4 (H 2 O) 2 ] and cis -[PtCl 4 (OH) 2 ] 2– . The computed Pt–Cl distance trans to a water molecule at 2.2778 Å in the former uncharged cis -[PtCl 4 (H 2 O) 2 ] species is considerably shorter than the corresponding bond in the cis -[PtCl 4 (OH) 2 ] 2– anion at 2.4124 Å, while the corresponding Pt–OH 2 and Pt–OH distances are 2.1424 and 2.0107 Å, respectively .…”

Atomic under-coordination fascinated catalytic and magnetic behavior of Pt and Rh nanoclusters

“…For instance, DFT calculations have been applied successfully to study the enhanced electrocatalytic activity of mushroom-like Pt clusters on the Pd-shell over Au core NPs, 23 as well as the isotope shifts in Pt and Rh NMR spectra. 24 Previously, we have successfully applied this method to study the electronic properties of Au, 25 Ag, 26 and Cu 26 nanoclusters. Here, we report consistency in trend between DFT calculations and the experimental observations on the local bond contraction, charge transfer, lattice strain, CLS, valence electron polarization, as well as magnetization of Pt and Rh nanoclusters.…”

Computational Insight into 103Rh Chemical Shift–Structure Correlations in Rhodium Bis(phosphine) Complexes

“…Interestingly, even though the 103 Rh chemical shift span is narrow, ca. 40 ppm, the computed values still correlate with average Rh–P bond distances at the picometer scale (Figure b) …”