Study On The Classification And Characteristics Of Borate Structure

On the basis of their abundant structures, borates are widely used as laser materials,luminescence host materials and non-linear optical materials, and have therefore attractedconsiderable attention.In borate crystals, the boron atoms are hybridized forming sp² structures with trigonalsymmetry [Bφ₃] or sp³ structures exhibiting tetrahedral symmetry [Bφ₄] (φ=O^2-, OH^-). These[Bφ₃] and [Bφ₄] polyhedra can be connected via common comers (oxygen atoms) to formrigid boron-oxygen groups. These groups represent the anionic repeat units of the crystalstructures and are called fundamental building blocks (FBBs). The FBBs can polymerize intocomplex borate polyanions such as infinite chains, layers and framework anions. Therefore,borates have the abundant structures. In this paper, we take the Inorganic Crystal StructureDatabase (ICSD, 2004) as data source and analyze all available borate structures by dint ofDiamond and Mercury softwares. The conclusions of the paper show:1. The fundamental building blocks of all available borates can be divided into 6 types:single Bφ₃ or Bφ₄ FBB, branched FBB, normal-ring FBB, bridge-ring FBB, helical-ring FBBand combined-ring FBB.2. A simpler and convenient algebraic description is proposed to describe the topologicalstructure of FBBs and their polymerization in borates.3. On the basis of the topological structure of FBB and their polymerization in borates(isolate, chain, layer and framework), a new systematic borate-classification is put forward,and all available borates are classified.4. The structures of borates and borophosphates are primarily influenced by polyanions,and in borates M_xB_yA_z the number of coordination of B atoms increases with theelectronegativity of A atoms.5. Based on the abundant characteristic structures and the high percentage ofnon-centrosymmetric compounds, borates and porophosphstes are the good field to search fornew non-linear optical materials.