Fluorooxoborate

Fluorooxoborate is one of a series of anions or salts that contain boron linked to both oxygen and fluorine. Several structures are possible, rings, or chains. They contain [BO_xF_4−x]^(x+1)− units BOF₃²⁻ BO₂F₂³⁻, or BO₃F₁⁴⁻. In addition there can be borate BO₃ triangles and BO₄ tetrahedrons. These can then be linked by sharing oxygen atoms, and when they do that, the negative charge is reduced. They are distinct from the fluoroborates in which fluorine is bonded to the metals rather than the boron atoms. For example, KBBF, KBe₂BO₃F₂ is a fluoroborate and has more fluorine and oxygen than can be accommodated by the boron atom.

Common properties are a wide range of transparency from deep ultraviolet (DUV) to near infrared (NIR); non-linear optical response, meaning that a high-intensity light will have some power converted to double the frequency; birefringence. The transparency deep into the ultraviolet corresponds to a large band gap, whereby it takes a lot of energy to shift an electron in the material.^[1]

Compared to borates, fluorooxoborates are more likely to have lower dimensional structures such as layers or chains, as there are fewer oxygen connections available. Fluorooxoborates are more likely to be noncentrosymmetric as adding one fluorine atom to a boron reduces symmetry.