You can find information on this topic in:

J.A. Peters, Interactions between boric acid derivatives and saccharides in aqueous media; structures and stabilities of resulting esters

Coord. Chem. Rev. 268 (2014) 1–22. DOI: 10.1016/j.ccr.2014.01.016.

In Section 3 (Interactions between bor(on)ic acids and simple inorganic anions), self-association of borc acid is reviewed.

Mahshid,

This is about right, from my experience the signal of boric acid in dmso-D6 appears as a relatively broad singlet at 19.9 pm in 11B NMR.