Semiempirical INDO method has been used for calcns. on four-electron Keggin structure heteropoly blue molybdosilicate. The frontier mol. orbitals, orbital energies, bond orders, and atomic charges have been obtained. It is indicated that the structure of the heteropoly blue molybdosilicate with Keggin structure is distorted. The highest occupied orbitals in which there is more composition of bridge oxygen Ob and Oc are consisted of orbitals of all atoms in the mol. Mulliken anal. shows that the reduced Mo atom has more neg. charge.

Key words: MOLECULAR ORBIT, QUANTUM CHEMISTRY, MOLYBDENUM COMPLEX, SILICON COMPLEX, HETEROPOLY BLUE