I am trying to calculate chemical shifts for Tellurium in an organotellurium compound with Gaussian16 but the calculated values do not match experimental values at all. I know that NMR calculation with heavier atoms can be problematic because of relativistic effects but there is another problem I can not make sense of. I calculated chemical shifts (B3LYP/def2-TZVP, GIAO) for a set of other organotellurium compounds and the values I obtain are nowhere around the calculated reference values, which were obtained using a similiar method. I know that to obtain a chemical shift from chemical shieldings, one has to calculate the difference between a reference compound (for Te-NMR: Dimethyltelluride, calculated isotropic shielding value: 387.4 ppm) and the compound of interest. But using this relation I obtain values that do not match any of the experimental or theoretical values I have seen so far. Did anyone do similiar calculations for Te compounds and is there something I am not getting right ?
The references I compared my results to are:
The output with the tellurium chemical shieldings for the reference compound (Me2Te) looks like this:
SCF GIAO Magnetic shielding tensor (ppm): 1 Te Isotropic = 384.9991 Anisotropy = 39.7993 XX= 411.5320 YX= -0.0030 ZX= -0.0004 XY= -0.0014 YY= 371.8145 ZY= 0.0002 XZ= -0.0003 YZ= 0.0002 ZZ= 371.6507 Eigenvalues: 371.6507 371.8145 411.5320
And for an organotellurium example (Tellurophene):
4 Te Isotropic = 379.3320 Anisotropy = 16.7719 XX= 390.5132 YX= -0.0006 ZX= 0.0000 XY= 0.0001 YY= 367.0601 ZY= 0.0000 XZ= 0.0000 YZ= -0.0000 ZZ= 380.4225 Eigenvalues: 367.0601 380.4225 390.5132
Those results were obtained using Gaussian16 on the B3LYP/def2-TZVP level and the GIAO method. The structures were optimized on the same level.