Systematic investigation of density functional theory methods for diorganotin 1,3-dithiole-2-thione-4,5-dithiolate complexes, R2Sn(dmit).

CONTEXT: Organotin complexes have been extensively studied due to their versatile structural features and potential applications in catalysis, materials science, and bioinorganic chemistry. Among them, compounds containing Sn-S interactions are of particular interest, as the tin-sulfur bond strongly affects both the stability and the electronic properties of the complexes. In addition, theoretical studies on 1,3-dithiole-2-thione-4,5-dithiolate systems have attracted considerable attention because of their potential technological applications.

METHODS: Density functional theory calculations were performed to evaluate the performance of different exchange-correlation functionals in describing the structural and spectroscopic properties of R2Sn(dmit) complexes. A total of 36 levels of theory were assessed for geometry optimization by combining 12 density functionals with three basis sets (def2-SVP, def2-TZVP, and def2-QZVP). The calculated geometric parameters were compared with experimental crystallographic data using statistical metrics including mean deviation, mean absolute deviation, standard deviation, and root mean square deviation. The results show that the choice of exchange-correlation functional has a greater influence on the accuracy of the optimized geometries than the basis-set size, with PBE/def2-SVP, BP86/def2-SVP, and M06-2X/def2-TZVP providing the best overall agreement with the experimental structures. Harmonic vibrational frequencies were corrected by linear scaling and compared with the experimental infrared spectra, demonstrating that BP86 and PBE consistently produced the lowest statistical deviations, whereas increasing the basis-set size beyond the triple-ζ level provided only marginal improvements. The 119Sn NMR chemical shifts were calculated using the ZORA, DKH, and X2C relativistic Hamiltonians. The double-hybrid B2PLYP-D3 functional yielded the lowest absolute errors overall within the investigated dataset. For most global and range-separated hybrid functionals (e.g., CAM-B3LYP, M06-2X, and ωB97X-D3), as well as the GGA functional BP86, the X2C Hamiltonian provided satisfactory agreement with the experimental data within the investigated dataset, yielding R2 values of 0.984-0.986, regression slopes moderately close to unity, and low mean absolute deviations. The chemical-shift range covered by the investigated systems represents only a subset of the full 119Sn chemical-shift range, reflecting the specific chemical space considered in this study. Overall, the results demonstrate that computationally efficient GGA functionals provide a favorable balance between accuracy and computational cost for geometry optimization and vibrational frequencies, whereas the prediction of 119Sn NMR chemical shifts is strongly influenced by the choice of relativistic treatment, B2PLYP-D3/ZORA being the top-performing individual protocol and X2C providing the most consistent agreement with the experimental data for most functionals for the systems investigated.