A density functional theoretical study aimed at correlating the chemical shifts of interstitial atoms and electronic structures of main-group-centered hexazirconium halide clusters has been performed and analyzed within the framework of perturbation theory. The influence of bridging halides on electronic structure was studied with two series of model compounds [(Zr(6)Z)X-12](H2O)6(n+) (Z = B, C; X = Cl, Br, I). The effect of terminal ligands on electronic structure was investigated with model compounds [(Zr6B)Cl-12]L-6(+) (L = H2O, PH3, HCN, and OPHA There is a qualitative inverse proportionality between the chemical shifts and the calculated energy gaps between two Kohn-Sham orbitals, DeltaE(t(lu)*-t(lu)), where t(lu) and t(lu)* orbitals are the bonding and antibonding orbitals that result from the interaction between the zirconium cage bonding orbitals and the interstitial 2p orbitals. Chemical shielding properties of the interstitial atoms were further calculated with the gauge-including atomic orbitals (GIAO) method.