Prediction of Pt-195 NMR chemical shifts of dissolution products of H-2[Pt(OH)(6)] in nitric acid solutions by DFT methods: how important are the counter-ion effects?

摘要

Pt-195 NMR chemical shifts of octahedral Pt(IV) complexes with general formula [Pt(NO3)(n)(OH)(6-n)](2-), [Pt(NO3)(n)(OH2)(6-n)](4-n) (n=1-6), and [Pt(NO3)(6-n -m)(OH)(m)(OH2)(n)](-2+n-m) formed by dissolution of platinic acid, H-2[Pt(OH)(6)], in aqueous nitric acid solutions are calculated employing density functional theory methods. Particularly, the gauge-including atomic orbitals (GIAO)-PBE0/segmented all-electron relativistically contracted-zeroth-order regular approximation (SARC-ZORA)(Pt) 6-31G(d,p)(E)/Polarizable Continuum Model computational protocol performs the best. Excellent second-order polynomial plots of (calcd)(Pt-195) versus (exptl)(Pt-195) chemical shifts and (calcd)(Pt-195) versus the natural atomic charge Q(Pt) are obtained. Despite of neglecting relativistic and spin orbit effects the good agreement of the calculated Pt-195 chemical shifts with experimental values is probably because of the fact that the contribution of relativistic and spin orbit effects to computed sigma(iso) Pt-195 magnetic shielding of Pt(IV) coordination compounds is effectively cancelled in the computed Pt-195 chemical shifts, because the relativistic corrections are expected to be similar in the complexes and the proper reference standard used. To probe the counter-ion effects on the Pt-195 NMR chemical shifts of the anionic [Pt(NO3)(n)(OH)(6-n)](2-) and cationic [Pt(NO3)(n)(OH2)(6-n)](4-n) (n=0-3) complexes we calculated the Pt-195 NMR chemical shifts of the neutral (PyH)(2)[Pt(NO3)(n)(OH)(6-n)] (n=1-6; PyH=pyridinium cation, C5H5NH+) and [Pt(NO3)(n)(H2O)(6-n)](NO3)(4-n) (n=0-3) complexes. Counter-anion effects are very important for the accurate prediction of the Pt-195 NMR chemical shifts of the cationic [Pt(NO3)(n)(OH2)(6-n)](4-n) complexes, while counter-cation effects are less important for the anionic [Pt(NO3)(n)(OH)(6-n)](2-) complexes. The simple computational protocol is easily implemented even by synthetic chemists in platinum coordination chemistry that dispose limited software availability, or locally existing routines and knowhow. Copyright (c) 2016 John Wiley & Sons, Ltd.