DFT calculations of the electric field gradient at the tin nucleus as a support of structural interpretation by 119Sn Mossbauer spectroscopy

DFT calculations, using an all-electron basis set and with full geometry optimization, were performed on 34 Sn-II and Sn-IV compounds of known structure and Sn-119 Mossbauer parameters, to obtain the theoretical values of the electric field gradient components, V-xx, V-yy and V-zz, at the tin nucleus. These were used to determine the quantity V=V-zz [1+ 1/3 (v(xx)-v(yy/)v(zz))(2)](1/2) for each investigated compound, which is related to the quadrupole splitting (Delta E) parameter according to Delta E = 1/2eQV, where e is the electronic charge and Q is the quadrupole moment of the tin nucleus. The linear fitting of the correlation plot of the experimental Delta E, versus the corresponding calculated V values, produced a slope that is equal to 0.93 +/- 0.03 and a correlation coefficient R = 0.982. The value of Q obtained, 15.2 +/- 4.4 fm(2), is in agreement with that previously experimentally determined or calculated by analogous procedures. The calculation method is able to establish the sign of the electric field gradient component V, in agreement with the sign of Delta E determined experimentally by Mossbauer-Zeeman spectroscopy. The calculated structural parameters are in good agreement with the corresponding experimental data, determined by X-ray crystallography in the solid state, with average structural deviations of about 3% for bond lengths and angles in the tin environment. Calculated values of Delta E were obtained from the calibration fitting constant and from the values of V By comparing experimental and calculated Delta E parameters, the structure assignment of configurational isomers was successful in two test cases, in agreement with the experimental X-ray crystallographic structures. These results indicate that the method can be used as a tool to support the routine structure interpretation of tin compounds by Sn-119 Mossbauer spectroscopy.