Effects of heteroatoms on electronic states of divanadium-substituted gamma-Keggin-type polyoxometalates (TBA)(4) [gamma XV2W10O38(mu-OH)(mu-OR)] (X = Ge, Si; R = Me, Et, n-Pr, H; TBA = tetra(n-butyl)ammonium) and (TBA)(4)[gamma-XV2W10O38(mu-O)] (X = Ge, Si) were investigated, using a combination of nuclear magnetic resonance spectroscopy and density functional theory (DFT) calculations. Both the substitution of SiO4 heteroatom units with larger GeO4, ones and the introduction of more electronegative alkoxo groups in place of hydroxo groups resulted in deshielding of the vanadium nuclei. DFT calculations using the Def2-SVP basis set at TPSSh level of theory could well-reproduce the anionic moieties of a series of divanadium-substituted gamma-Keggin-type polyoxometalates, and the estimated chemical shifts approximately reproduced the experimental ones with the individual gauge localized orbital method (SO-IGLO) taking the spin orbit interaction into account. The magnetic shielding (sigma) consists of sigma(d) + sigma(p) + sigma(SD) + sigma(FC), where sigma(d), sigma(p), sigma(SD) and sigma(FC) are diamagnetic, paramagnetic, spin-dipolar, and Fermi contact terms, respectively. The sigma(p) changed much among (TBA)(4)[gamma-XV2W10O38(mu-OH2)], (TBA)(4)[gamma-XV2W10O38 (mu-OH) (mu-OR), and (TBA)(4)[gamma-XV2W10O38(mu-O)], while sigma(d), sigma(SD), and sigma(FC) did not change much. Therefore, the sigma(p) largely contributed to the magnetic shielding. Moreover, sigma(p) consisted of the occupied occupied transitions (s-terms) and the occupied virtual ones (u-terms), and the u-terms were predominant for sigma(p). The most contributing occupied localized orbital consisted of the d(z)(2) orbital of vanadium, the p(z) orbital of terminal oxygen related to the V=0 bond, and the p(z) orbital of oxygen of the XO4 unit, whereas the two virtual localized orbitals consisted of the d(yz) orbital of vanadium and the p(y) orbital of terminal oxygen. Analysis of the structural and electronic characteristics of a series of divanadium-substituted gamma-Keggin-type POMs revealed a linear correlation between both V-51{H} chemical shifts and the reciprocal values of the energy gaps between the corresponding XO4-predominant orbital HOMOs-X and the LUMOs+X (X = 0, 1, or 2). All these results indicate that neighboring XO4 units weakly interact with the addenda atoms and control the electronic states of polyoxometalates and the magnetic shielding of their addenda atoms.