A new complex K~5H[Co~4(VW~9O~3~3)~2]·5H~2O was prepared and its structure was determined by X-ray diffraction analysis. The anion has α-B-Keggin structure. Two (VW~9O~3~3)^7^- moieties (α-B isomers) are linked via four Co(Ⅱ)O~6 groups. The single crystal of the title complex is monoclinic P2~1~/~n with a=1.2307(3)nm, b=2.1250(4)nm, c=1. 5817(3)nm, β=91.86(3)°, V=4.1343(14)nm^3, R=0.0895, R~W=0.2180.

Key words: VANADIUM OXIDE, TUNGSTEN OXIDE, COBALT COMPOUNDS, POTASSIUM COMPOUNDS, SYNTHESIS, STRUCTURE CHARACTERISTICS, THERMAL STABILITY