A series of borosilicates was synthesized, where the structure of the borosilicate core was easily modulated using two strategies: blocking of condensation sites and controlling the stoichiornetry of the reaction. Thus, on the one hand, the condensation of phenylboronic or 3-hydroxyphenylboronic acid with diacetoxysilylalkoxide [((BuO)-Bu-t)(Ph3CO)Si(OAc)(2)] led to the formation of borosilicates ((BuO)-Bu-t)(Ph3CO)Si{(mu-O)BPh}(2)(mu-O) (1), [{((BuO)-Bu-t)(Ph3CO)Si(mu-O)BPh(mu-O)}(2)] (2), and [{((BuO)-Bu-t)(Ph3CO)Si(mu-O)B(3-HOPh)(mu-O)}(2)] (3) with a cyclic inorganic B2SiO3 or B2Si2O4 core, respectively. On the other hand, the reaction of phenylboronic acid with triacetoxysilylalkoxide (Ph3CO)Si(OAc)(3) in 3:2 ratio resulted in the formation of a cagelike structure [{(Ph3CO)Si(mu-O)(2)BPh(mu-O)}(2)] (4) with B4Si4O10 core, while the reaction of the boronic acid with silicon tetraacetate generated an unusual 1,3-bis(acetate)-1,3-diphenyldiboraxane PhB(mu-O)(mu-O,O'-OAc)(2)BPh (5). Additionally, compound 1 was used to evaluate the possibility to form N -> B donor-acceptor bond between the boron atom in the borosilicates and a nitrogen donor. Thus, coordination of 1 with piperazine yielded a tricyclic [{((BuO)-Bu-t)(Ph3CO)Si(OBPh)(2)(mu-O)}(2)center dot C4H10N2] compound 6 with two borosilicate rings bridged by a piperazine molecule. Finally, the processes involved in the formation of the six- and eight-membered rings (B2SiO3 and B2Si2O4) in compounds 1 and 2 were explored using solution H-1 NMR studies and density functional theory calculations. These molecules represent to the best of our knowledge first examples of cyclic molecular borosilicates containing SiO4 units.