It is very difficult to predict the structures of the borate anions from the stoichiometry of the complex borates. Anhydrous borates are prepared by fusing boric acid and metal oxides. The hydrated borates may be cryallized form aqueous solutions. The general composition of borates : KB₅O₈.4H₂O. CaB₂O₄, Na,B4O₇.10H₂O gives very  little information about the strucutes of the borate anions. They are generally cyclic or linear polymers formed by linking together of BO₃ and/or BO₄ units through shard oxygen atoms. Bortes containing one or more than one boron atom (upto 5B atoms) or polydimentsional networks (glasses) are known to exist. They mainly consist of :

(i)    Boron atom linked either to three oxygen atoms (BO₃ unit) or four oxygen atoms (BO₄ tetrahedron).
(ii)    Polynuclear anions are formed by corner sharing of boron-oxygen triangles or tetrahedrons.
(iii)    These units can be prorogated to various extents.
                                          Ring (K₃B₂O₄)                                  Chain (CaB₃O₆)

It may be noted that contrast to borates, the carbonate ion does not form polymeric strucutes. This may probably be attributed to the formation of strong C-O π bonds.

Borax, which is normally written as Na₂B₄O₇.10H₂O contains tetranuclear units [B₄O₅(OH)₄]₂^- comprising of BO₄ and BO₃ units. Borax should therefore be formulated as Na₂[B₄O₅(OH)₄]₄H₂O.

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