The generation of magic number silica clusters [(SiO2)(n)O2H3](-) with n = 4 and 8 by XeCl laser (308 nm) ablation of porous siliceous materials is reported. The production of magic cluster [(SiO2)(4)O2H3](-) can be enhanced by sample selection and experimental optimization so that it becomes the most prominent species in silica clusters. To study the structure of the magic cluster [(SiO2)(4)O2H3](-), we performed structural optimization for the neutral bare cluster (SiO2)(4), the neutral complex cluster (SiO2)(4)O2H4, and the anionic cluster [(SiO2)(4)O2H3](-) at the HF/6-31G** level. It was found that the ground state of the bare silica tetramer has a linear chain structure whereas a pseudotetrahedral cage-like structural isomer of Sq symmetry is most stable for the complex cluster (SiO2)(4)O2H4 The stabilization of the three-dimensional (3D) structure can be attributed to the active participation of the O2H4 group in chemical bonding during cluster formation. Our theoretical calculation and bonding analysis indicate that the magic number anionic cluster [(SiO2)(4)O2H3](-) might also take a pseudotetrahedral structure similar to (but with a different symmetry) that of the neutral precursor (SiO2)(4)O2H4 as the ground state in which the valence, coordination, and bonding characteristics of all the constituent atoms are nearly fully satisfied.