Three novel pentacoordinate silicon compounds with SiO5 skeletons containing SiOH or SiOSi groups were synthesized: triethylammonium bis[benzilato(2-)-O-1,O-2]hydroxosilicate (1; isolated as rac-1), anilinium bis[benzilato(2-)-O-1,O-2]hydroxosilicate [2; isolated as a conglomerate consisting of (Lambda)-2 . THF and (Delta)-2 . THF], and anilinium tetrakis[benzilato(2-)-O-1,O-2]-mu-oxo-disilicate (3; isolated as rac-3 . 2CH(3)CN). The lambda(5)Si-hydroxosilicate and lambda(5)Si,lambda(5)Si'-mu-oxo-disilicate anions of these salts formally derive from the pentahydroxosilicate-(1-) anion [Si(OH)(5)](-) and its anhydride [(HO)(4)Si-O-Si(OH)(4)](2-) respectively. All compounds were characterized in solution (H-1, C-13 and Si-29 NMR) and in the solid state (Si-29 VACP/MAS NMR, crystal structure analyses).