Context : Recent studies have confirmed the long standing suspicion that M22 shares a metallicity spread and complex chemical enrichment history similar to that observed in \omega Cen .
M22 is among the most massive Galactic globular clusters and its colour-magnitude diagram and chemical abundances reveal the existence of sub-populations .

Aims : To further constrain the chemical diversity of M22 , necessary to interpret its nucleosynthetic history , we seek to measure relative abundance ratios of key elements ( carbon , nitrogen , oxygen , and fluorine ) best studied , or only available , using high-resolution spectra at infrared wavelengths .

Methods : High-resolution ( R = 50,000 ) and high S/N infrared spectra were acquired of nine red giant stars with Phoenix at the Gemini-South telescope .
Chemical abundances were calculated through a standard 1D local thermodynamic equilibrium analysis using Kurucz model atmospheres .

Results : We derive [ Fe/H ] = - 1.87 to - 1.44 , confirming at infrared wavelengths that M22 does present a [ Fe/H ] spread .
We also find large C and N abundance spreads , which confirm previous results in the literature but based on a smaller sample .
Our results show a spread in A ( C+N+O ) of \sim 0.7 dex .
Similar to mono-metallic GCs , M22 presents a strong [ Na/Fe ] - [ O/Fe ] anticorrelation as derived from Na and CO lines in the K band .
For the first time we recover F abundances in M22 and find that it exhibits a 0.6 dex variation .
We find tentative evidence for a flatter A ( F ) -A ( O ) relation compared to higher metallicity GCs .

Conclusions : Our study confirms and expands upon the chemical diversity seen in this complex stellar system .
All elements studied to date show large abundance spreads which require contributions from both massive and low mass stars .