Unusual Formations of Superoxo Heptaoxomolybdates from Peroxo Molybdates.

Abstract Two novel dioxygen heptaoxomolybdates K 5 [Mo 7 O 22 (O 2 )(OH)]Cl·6H 2 O ( 1 ) and K 5 [Mo 7 O 22 (O 2 )(O 2 )]·8H 2 O ( 2 ) were isolated from the solution of peroxo molybdate accidently. The solids were characterized by IR, EPR and X-ray single crystal analysis. Complex 1 contains a superoxo group with a short bond distance 1.27(1) A, while 2 is a mixed complex with peroxo and superoxo groups [1.43(1), 1.27(1) A]. All of the dioxygen groups coordinate to molybdenum atoms in side-on (η 2 ) fashion. The two complexes are short-lived and will decompose into peroxo molybdates K 5 [Mo 7 O 21 (O 2 ) 2 (OH)]·6H 2 O ( 3 ) and K 6 [Mo 7 O 22 (O 2 ) 2 ]·9H 2 O ( 4 ) very quickly.