We present a DFT approach for precise estimation of the intermolecular effects on the experimental and calculated 13C NMR shifts for a series of 5-spiro-2,4-dithiohydantoins (1–5), both in solid state and in solution. It has been found that the used B3LYP/6-31+ G** method gives very good agreement with the experimental structural and the NMR parameters, provided the intermolecular hydrogen bonds are properly considered. For correct description of the experimental NMR shifts in solid state we have initially used the isolated-molecule and the cluster approaches for GIAO calculations of the NMR shifts, followed by periodic boundary condition calculations of the structure and the nuclear magnetic shielding constants by the GIPAW method implemented in the Quantum Espresso code. The best agreement with the experimental solid state data is obtained for the optimized small cluster (a trimer of molecules) in the calculations using the atom-centered orbitals. Excellent agreement between the 13C CPMAS NMR and the GIPAW calculated shift is obtained for fully relaxed bulk structures of compounds 1–5. This has been used as a final verification of the proposed solid state structure of compound 5 whose crystal structure is unknown yet.
The authors are grateful for the calculation time, granted on PHYSON computer cluster, operating under the National Science Fund of Bulgaria grants VU-F-205/2006, DO-02-136/2008 and DO-02-167/2008 and for the help and support by Prof. Ana Proykova and Dr. Stoyan Pisov. The financial support of the Bulgarian National Science Fund for the acquisition of the used NMR equipment (Projects UNA-17/2005 and DRNF02-13/2009) is gratefully acknowledged. Part of the work is also supported by DAAD thanks to the kind hospitality of Prof. M. Springborg.
©2016 Walter de Gruyter Berlin/Boston