Information stored in the Cambridge Crystallographic Data Centre shows that anti-anti conformation is common for bis(organothiophosphoryl) dichalcogenides. In view of the 1-4 repulsion, the syn-syn conformation of the S-1=P-X-X-4-P=S (X = S and Se) backbone is unfavorable. However, in compounds with at least one phenyl group directly bonded to the phosphorus, such as bis[tert-butyl(phenyl)thiophosphinyl] disulfide (Knopik, P. et al. J. Chem. Sec., Dalton Trans. 1993, 2749), bis(diphenylthiophosphinyl) disulfide (Gallacher, A. C. et al. Acta Crystallogr. 1993, C49, 1793) and bis[tert-butyl(phenyl)thiophosphinyl] diselenide (this work) there is the syn-syn geometry caused by the aromatic-aromatic interactions. Bis[tert-butyl(phenyl)thiophosphinyl] diselenide is monoclinic, space group C2/c with a = 20.424(2) Angstrom, b = 9.373(1) Angstrom, c = 12.907(1) Angstrom, V = 2406.4(2) Angstrom(3), D-c = 1.525 (2) g/cm(3), and Z = 4. Refinement using 2351 reflection for 118 variables gives R = 0.047. We have used high-resolution Se-77 MAS NMR to study the structural properties of the compound. The principal elements T-ii of the Se-77 effective dipolar/chemical shift tensor were calculated from the intensities of the spinning sidebands. The values of the anisotropy and asymmetry parameters reflect the distortion of the environment of selenium. For a series of bis(organothiophosphoryl) diselenides the T-33 tensor component gives the largest contribution to the isotropic chemical shifts and the span parameter Omega reflects the strength of the diselenide bond. Molecular packing significantly influences the intramolecular dynamics of the aliphatic and aromatic groups. The C-13 dipolar dephasing experiment and line shape analysis of the H-1-H-2 CP/MAS spectra of selectively H-2-labeled compounds show that the phenyl groups are static as a result of the aromatic-aromatic interaction, while the tert-butyl groups are under a fast motional regime, with C-3v jumps around the P-C and C-C bonds.