Bond analyses of borates from the Inorganic Crystal Structure Database.

Various fundamental building blocks (FBBs) are observed in the crystallographic structures of oxoborates available in the Inorganic Crystal Structure Database, Version 1.3.3 (2004); the occurrence of borate groups with low complexity is dominant. Bond-valence parameters d(0) of B-O bonds in 758 oxoborates with various FBBs have been calculated using the bond-valence sum model. Some discrepancies in the d(0) values obviously occur if the detailed configurations of FBBs in borate crystals are considered; d(0) is sensitive to the chemical bonding structure of B atoms in the crystallographic framework. Moreover, d(0) values are affected by the existence of interstitial atoms and the substitution of other anionic groups. In addition, the d(0) parameters for B-N, B-S, B-P and B-F bonds are also calculated statistically. Some suitable d(0) data for various borate FBBs are recommended according to their particular configurations, especially for those with low complexity. On the basis of the proposed linear relationship between calculated nonlinear optical (NLO) coefficients of borates and the current d(0) values for various FBBs, it is found that the d(0) values may be regarded as a useful parameter for pre-investigating the NLO properties of borates, leading to an efficient structural evaluation and design of novel borates.