The controllable synthesis of two vanadium-containing polyoxoniobate-based three-dimensional organicinorganic hybrid compounds, [Co(pn)(2)](4)[(HPNb10V2O40)-O-IV((VO)-O-IV)(4)]center dot 17H(2)O (1) and [Co(pn)(2)](5)[PNb12O40((VO)-O-IV)(6)](OH)(7)center dot 15H(2)O (2), where pn = 1,2-diaminopropane, is realized by changing the hydrothermal temperature or adding N-(aminoethyl)piperazine as an additive. Both compounds 1 and 2 are structurally characterized by single-crystal/powder X-ray diffraction and IR and X-ray photoelectron spectroscopy. Compound 1 features a new divanadium-substituted Keggin polyoxoniobate capped by four vanadyl groups, and the polyanion in 2 exhibits the highest coordination number (10-connected) in polyoxoniobate chemistry. Moreover, the photocatalytic activities of 1 and 2 for hydrogen evolution are preliminarily assessed.