LAUSR

The energies and structural and spectroscopic characteristics of endohedral and exohedral isomers of oxovanadate complexes with MO4n− tetraoxo anions located in the inner and outer spheres of the V20O50 cluster have been calculated by the density functional theory method (B3LYP). It has been demonstrated that, among the endohedral MO4@V20O50n− clusters with strong multiply charged anions (VO43−, CrO42−, PO43−, SO42−, BO45−, etc.), the isomer in which a distorted “guest” tetrahedron MO4 is displaced from the cluster center and bonded to the V20O50 cage through two internal oxygen bridges M−O*−V is the most favorable one. Among the exohedral analogues MO4 · V20O50n−, the most favorable isomer contains the guest in the capping position bonded to the cage from the outside through three external M−O−V bridges. The latter isomer is more favorable than the former; however, the “exo–endo” transition between them for the clusters with multiply charged anions is accompanied by small changes in energy of ∼2−10 kcal/mol. Singly charged perchlorate and perbromate anions ClO4- and BrO4− in the inner sphere of V20O50 are unstable: during optimization, they are “reduced” with decomposition into atoms and concurrent “inner-sphere oxidation” of V20O50 to V20O54 with four peroxide cage bridges V−O−O−V. Charge transfer and specific features of the host–guest interaction in oxovanadate complexes and trends in the properties of endo- and exohedral isomers as a function of the charge and bond character of guest anions are discussed.