Fluorooxoborate is one of a series of anions or salts that contain boron linked to both oxygen and fluorine.
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.
When dissolved, the nature of the fluorooxoborate ions present depends on the boron to oxygen ratio.
Above this it decomposes to BF3 boric oxide and Sn3[B3O7]F.[5] PbB2O3F2[4] contains two-dimensional sheets of BFOB pairs connected by four oxygen atoms to adjacent units.
[1] crystal system rhombohedral space group P31m 220 nm UV cutoff[1] BaB2O3F2 contains a double chain of -BO-O-BF-[1] The formula weight is 244.96.
[1] KB3O4F2 has a monoclinic crystal with space group P21/n with unit cell parameters a=4.6437 b=17.243 c=6.4301 β=102.660°.
[16] Ammonium, rubidium, and caesium salts also exist: NH4[B3O3F4(OH)], Rb[B3O3F4(OH)] and Cs[B3O3F4(OH)].
[17] NH4B4O6F, (ABF)[4] RbB4O6F (RBF), CsB4O6F, (CBF)[4] For the rubidium and ammonium compounds the structure is orthorhombic.
It contains borate sheets with fluorine pointing up and down into the between layers that contains the cations NH4, Rb or Cs.
The units in the sheet are a BO3 triangle joined to a boroxine ring with an extra fluorine (B3O6F).
[18] KB3O4F2 has a monoclinic crystal with space group P21/n with unit cell parameters a=4.6437 b=17.243 c=6.4301 β=102.660°.
The birefringence is around 0.06 in the visible light region of the spectrum, but increases sharply in the UV t 0.093 at 200 nm.
Each of the other boron atoms has a side oxygen connection that is shared with other of the building blocks.
Li2Na0.9K0.1B5O8F2 contains a two dimensional sheet composed of units which are a pair of borixine rings fused at one boron atom.
Each ring has an extra fluorine atom, and shares two oxygen bridges to adjacent units.
The other ring has an extra fluorine atom and bridges via two oxygens to adjacent units.
[18] Crystal structure is monoclinic, space group P21/c formula weight 383.15; unit cell a=7.3898 b= 14.2142 c=10.2551Å β=93.419° Volume=1075.3 Z=4, density=2.367 namd gap=6.98 eV.
The outer pair of rings is linked with extra oxygen atoms at each end to form a ladder-shaped structure.
It has orthorhombic structure with space group Pnma; formula weight 717.28 a=9.2659 b= 16.3431 c= 6.6326 Å Volume 1004.40 Å3 Z= 2 Density 2.372.
[18] CsRbB8O12F2[7] It contains borate sheets with fluorine pointing up and down into the between layers which contain mixed rubidium and caesium.