A comparison of the square-planar complexes of group 10 (Pd-II, Pt-II) and 16 (Se-II, Te-II) centers with the tetraisopropyldiselenoimidodiphosphinate anion, [N((Pr2PSe)-Pr-i)(2)](-), is made on the basis of the results of a solid-state P-31, Se-77, Te-125, and Pt-195 NMR investigation. Density functional theory calculations of the respective chemical shift and N-14 electric field gradient tensors in these compounds complement the experimental results. The NMR spectra were analyzed to determine the respective phosphorus, selenium, tellurium, and platinum chemical shift tensors along with numerous indirect spin-spin coupling constants. Special attention was given to observed differences in the NMR parameters for the transition metal and main-group square-planar complexes. Residual dipolar coupling between N-14 and P-11, not observed in the solid-state P-31 NMR spectra of the Pd(II) and Pt(II) complexes, was observed at 4.7 and 7.0 T for M[N((Pr2PSe)-Pr-i)(2)](2) (M = Se, Te) yielding average values of R(P-31, N-11)eff = 890 Hz, C-Q(N-14) = 2.5 MHz, (1)J(P-11, N-14)(iso) = 15 Hz, alpha = 90 degrees, beta = 17 degrees. The span, Omega, and calculated orientation of the selenium chemical shift tensor for the diselenoimidodiphosphinate anion is found to depend on whether the selenium is located within a pseucloboat or distorted-chair MSe2P2N six-membered ring. The largest reported values of (1)J(Se-17, Se-77)(iso), 405 and 435 Hz, and (1)J(Te-125 Se-77)(iso), 1120 and 1270 Hz, were obtained for the selenium and tellurium complexes, respectively; however, in contrast a correspondingly large value of (1)j(Pt-115, Se-17)(iso) was not found. The chemical shift tensors for the central atoms, Se(II) and Te(II), possess positive skews, while for Pt(II) its chemical shift tensor has a negative K. This observed difference for the shielding of the central atoms has been explained using a qualitative molecular orbital approach.