Borate complexes basic units

The structural chemistry of anhydrous metal borates is also complex but, unlike the hydrated analogs, polyborate ions can be composed of dissimilar basic units. 

Borates can be viewed as complex salts in which the Lewis basicity of the structural unit must match the Lewis acidity of the interstitial complex to produce a stable structure. The relationship between basicity of the borate structural unit and its BO4/BO3 ratio was mentioned above, indicating that each specific structural unit has an associated basicity. It was recently shown that the Lewis basicity of borate structural units correlates with the average coordination number of the oxygen atoms they contain, counting H-bonds... 

Thus, there are numerous structural types of anhydrous borates. However, it is possible to reduce some of these complex structures to various combinations of the three types of the basic structural units mentioned above FSU, CSU, and CRP. 

Numerous anhydrous borate structures can be reduced to various combinations of three types of basic structural units 1) fundamental structural units, 2) combined basic structural units, and 3) full radicals of polyanions. The stability of the FSU, CSU and CRP units in solid and liquid borates is one of the most important issues, and will provide a better understanding of, and control of, phase formation in complex borate systems. 

---