# Fluoroiodate

A fluorooxoiodate or fluoroiodate is a chemical compound or ion derived from iodate, by substituting some of the oxygen by fluorine. They have iodine in the +5 oxidation state. The iodine atoms have a stereochemically active lone-pair of electrons. Many are non-centrosymmetric, and are second harmonic generators (SHG) of intense light shining through them. They are under investigation as materials for non-linear optics, such as for generating ultraviolet light from visible or infrared lasers.
Different ions include [IOF$_4$]$^−$, [IO$_2$F$_2$]$^−$, [IO$_3$F]$^{2−}$, and [I$_2$O$_5$F$_2$]$^{2−}$.
They are distinct from the fluoride iodates which are mixed anion compounds that do not have fluorine-iodine bonds.

## Properties

Fluoroiodates are transparent in visible, longer wave ultraviolet and some of the infrared electromagnetic bands.
Compared to iodate, the I-O bonds are shorter, and I-F bonds are longer in fluoroiodates. The I-F bond is about 0.2 Å longer than the I-O bond. The fluorine atoms repel each other in [IO$_2$F$_2$]$^−$ and are almost opposite each other. The ∠OIF angle is close to 90° and the oxygen atoms ∠OFO are at about 102°, so they resemble an octahedral arrangement, with two adjacent positions deleted.

## List

| formula | crystal | space group | unit cell | volume | density | band gap eV | SHG × KDP 1064 nm | comment |
| NH$_4$IO$_2$F$_2$ | orthorhombic | Pca2$_1$ | a=8.639 b=6.166 c=8.629 Z=4 | 459.7 | | 4.53 | 1.2 | |
| (NH$_4$)$_3$(IO$_2$F$_2$)$_3$·H$_2$O | orthorhombic | Pnma | a=15.102 b=12.685 c=7.369 Z=4 | 1411.8 | | 4.55 | no | |
| [C(NH$_2$)$_3$]$^+$[IF$_2$O$_2$]$^–$ | triclinic | P1 | a = 6.6890 b = 10.2880 c = 10.30.92 α = 105.447 β = 108.568 γ = 91.051° Z=4 | 644.08 | 2.650 | 4.81 | | explosive; birefringence Δn = 0.110 |
| (C(NH$_2$)$_3$)$_2$(I$_2$O$_5$F)(IO$_3$)(H$_2$O) | monoclinic | P2$_1$/c | a=7.4388 b=19.2679 c=11.0753 β=106.289° Z=4 | 1523.70 | | 4.49 | | birefringence Δn = 0.068 |
| NaIO$_2$F$_2$ | orthorhombic | Cmcm | a=6.929 b=7.274 c=7.350 Z=4 | 370.42 | | | 0 | |
| KIO$_2$F$_2$ | orthorhombic | Pca2$_1$ | a=8.3943 b=5.9792 c=8.4468 Z=4 | 423.95 | | | 0 | ferroelastic; when compressed on 001 axis IO$_2$F$_2$ units rotate with abc transforming to cba; |
| CoIO$_3$F | monoclinic | P2$_1$/n | a=4.9954 b=5.2110 c=12.5179 β=95.347° | | | | | |
| NiIO$_3$F | monoclinic | P2$_1$/n | | | | | | |
| ZnIO$_3$F | monoclinic | P2$_1$/m | | | | 4.2 | 0.00 | birefringence 0.219 at 546 nm |
| [GaF(H$_2$O)][IO$_3$F] | orthorhombic | Pca2$_1$ | a=13.954 b=6.9261 c=4.7629 | | | 4.34 | 10 | laser damage threshold 298.40 MW cm$^{−2}$; decompose 300 °C; dipole moment density: 0.0908 D Å$^{−3}$ |
| NaGaI$_3$O$_9$F | monoclinic | P2$_1$/c | _a=14.120 b=4.9149 c=13.63 β=112.968° Z=4 | 871.0 | 4.853 | 4.27 | 0 | $_∞$[Ga$_2$(IO$_3$F)$_2$(IO$_3$)$_4$]$^{2−}$ layers sandwiching Na$^+$; birefringence Δn$_{exp}$ ~ 0.203 at 1064 nm |
| RbIO$_2$F$_2$ | orthorhombic | Pca2$_1$ | a=8.567 b=6.151 c=8.652 Z=4 | 455.92 | | 4.2 | 4 | |
| SrI$_2$O$_5$F$_2$ | monoclinic | P2$_1$/c | a=10.462 b=7.272 c=8.306 β=109.699° Z=4 | 594.9 | | 3.68 | 0 | |
| Sr$_4$O(IO$_3$)$_3$(I$_3$O$_7$F$_3$)BF$_4$ | | R3c | a=9.7216 c=38.759 | | | | | absorption band at 250 nm; decompose 380 °C |
| CdIO$_3$F | | P2$_1$2$_1$2$_1$ | | | | 4.22 | 6.2 | |
| Rb$_2$MoO$_2$F$_3$(IO$_2$F$_2$) | orthorhombic | Cmc2$_1$ | a 11.806 b 10.128 c 7.6661 | | | 3.77 | 5 | |
| CsIO$_2$F$_2$ | orthorhombic | Pca2$_1$ | a=8.781 b=6.377 c=8.868 Z=4 | 496.58 | | 4.5 | 3 | |
| Cs$_3$(IO$_2$F$_2$)$_3$•H$_2$O | | Pnma | | | | 3.37 | 0 | |
| Cs(IO$_2$F$_2$)$_2$•H$_2$O•H3O | monoclinic | P2$_1$/c | | | | 2.77 | 0 | |
| CsIO$_4$ | | Pnma | | | | | 0 | |
| Cs$_2$VOF$_4$(IO$_2$F$_2$) | orthorhombic | Cmc2$_1$ | a=12.188 b=10.349 c=7.779 Z=4 | 981.2 | 4.100 | 2.88 | 5 | yellow at 1064 nm |
| Cs$_2$MoO$_2$F$_3$(IO$_2$F$_2$) | orthorhombic | Cmc2$_1$ | a =12.2153 b =10.4656 c =7.8560 | | | 3.43 | 4.5 | |
| BaIO$_3$F | monoclinic | P2$_1$/c | | | | 4.32 | 0 | |
| Ba(IO$_2$F$_2$)$_2$ | monoclinic | P2$_1$/c | a=10.747 b=7.161 c=9.086 β=93.748° Z=4 | 697.7 | | 3.99 | 0 | UV cut off 230 nm |
| BaI$_2$O$_5$F$_2$ | monoclinic | P2$_1$/c | a=10.750 b=7.599 c=8.598 β=109.753° | | | | | birefringence Δn= 0.174 at 1064 nm |
| BaIO$_2$F$_3$ | orthorhombic | Cmca | a=6.334 b=6.343 c=23.300 | | | 4.27 | 0 | birefringence Δn=0.133 at 1064 nm |
| Ba$_2$[GaF$_5$(IO$_3$F)] | monoclinic | P2$_1$/c | a=7.5065 b=7.4160 c=14.5932 β=100.363° | | | | | birefringence Δn=0.068 at 550 nm; UV edge 230 nm; transparent 0.34–11.9 μm |
| CaCe(IO$_3$)$_3$(IO$_3$F)F | orthorhombic | Pna2$_1$ | a=11.068 b=18.15 c=6.0301 Z=4 | 1211.3 | 5.033 | 2,72 | 5 | pale-yellow; birefringence 0.071 at 1064 nm SHG 5×KDP at 1064 nm |
| Rb$_2$WO$_2$F$_3$(IO$_2$F$_2$) | orthorhombic | Cmc2$_1$ | a=11.726 b=10.188 c=7.666 | | | 4.42 | | |
| Cs$_2$WO$_2$F$_3$(IO$_2$F$_2$) | orthorhombic | Cmc2$_1$ | a=12.1122 b=10.6192 c =7.8333 | | | 4.29 | | |
| Pb$_4$O(IO$_3$)$_3$(I$_3$O$_7$F$_3$)BF$_4$ | | R3c | a =9.8184 c =38.867 | | | | | absorption band at 283 nm; decompose 300 °C |
| KBi$_2$(IO$_3$)$_2$F$_5$ | monoclinic | P2$_1$ | a=5.687 b = 5.864 c = 14.815 β=100.095º Z = 2 | 486.5 | 6.157 | | | colourless |
| RbBi$_2$(IO$_3$)$_2$F$_5$ | monoclinic | P2$_1$ | a=5.7347 b = 5.9095 c = 15.117 β=100.263º Z = 2 | 506.20 | 6.221 | | | colourless |
| CsBi$_2$(IO$_3$)$_2$F$_5$ | monoclinic | P2$_1$ | a=5.750 b = 5.864 c = 15.640 β=100.509º Z = 2 | 523.8 | 6.313 | | | colourless |