The reaction of ZrCl4 with [gamma-SiW10O36](8-) in a potassium acetate buffer results in two different products depending on the reactant ratios. The trimeric species [Zr6O2(OH)(4)(H2O)(3)(beta-SiW10O37)(3)](14-) (1) consists of three beta(23)-SW10O37 units linked by an unprecedented Zr6O2(OH)(4)(H2O)(3) cluster with C, point group symmetry. The dimeric species [Zr4O2(OH)(2)(H2O)(4)(beta-SiW10O37)(2)](10-) (2) consists of beta(22)-and beta(12)-SiW10O37 units sandwiching a Zr4O2(OH)(2)(H2O)(4) cluster, which also has C, symmetry. Polyanion 1 contains more zirconium centers than any other polyoxometalate known to date.