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

Abstract

Zero-point vibrationally averaged (rg0) structures were computed at the PBE0/SDD/6-31G* level for the [Pt35Cln37Cl5–n(H218O)]− (n = 0–5), cis-Pt35Cln37Cl4–n(H218O)(H216O) (n = 0–4), fac-[Pt35Cln37Cl3–n(H218O)(H216O)2]+ (n = 0–3), [Pt35Cln37Cl5–n(16/18OH)]2– (n = 0–5), cis-[Pt35Cln37Cl4–n(16/18OH)2]2– (n = 0–4), fac-[Pt35Cln37Cl3–n(16/18OH)3]2– (n = 0–3), cis-[Pt35Cln37Cl2–n(16/18OH)4]2– (n = 0–2), [Pt35Cln37Cl1–n(16/18OH)5]2– (n = 0–1), [Rh35Cln37Cl5–n(H2O)]2– (n = 0–5), cis-[Rh35Cln37Cl4–n(H2O)2]− (n = 0–4), and fac-Rh35Cln37Cl3–n(H2O)3 (n = 0–3) isotopologues and isotopomers. Magnetic shielding constants, computed at the ZORA-SO/PW91/QZ4P/TZ2P level, were used to evaluate the corresponding 35/37Cl isotope shifts on the 195Pt and 103Rh NMR spectra, which are known experimentally. While the observed effects are reproduced reasonably well computationally in terms of qualitative trends and the overall order of magnitude (ca. 1 ppm), quantitative agreement with experiment is not yet achieved. Only small changes in M–Cl and M–O bonds upon isotopic substitution, on the order of femtometers, are necessary to produce the observed isotope shifts.