AbstractThe principal elements δiiof31P and77Se chemical shift tensors for the structural analogues bis(dineopentoxythiophosphoryl) diselenide (1) and bis(dineopentoxythiophosphoryl) disulphide (2) were calculated from spinning sideband intensities employing the MASNMR program. From analysis of the31P NMR data it was concluded that replacement of sulphur by selenium has little influence on shielding parameters, anisotropy Δδ and span Ω. The asymmetry η and skewkare very similar if the geometry of SPXXPS unit (X = S, Se) is not changed.77Se NMR data are discussed in terms of PSeSeP unit geometry. The static spectra were recorded employing the CPECHO pulse sequence. It was found that this technique is useful both for the lineshape analysis and the calculation of the second moment. The experimental values ofM2dare 0.387 kHz2for diselenide 1 and 0.495 kHz2for disulphide 2. These values are consistent with those calculated from the van Vleck equation for polycrystalline m