We combine a catalog of wide binaries constructed from Gaia DR2 with [ Fe/H ] abundances from wide-field spectroscopic surveys to quantify how the binary fraction varies with metallicity over separations 50 \lesssim s / { AU } \lesssim 50 , 000 .
At a given distance , the completeness of the catalog is independent of metallicity , making it straightforward to constrain intrinsic variation with [ Fe/H ] .
The wide binary fraction is basically constant with [ Fe/H ] at large separations ( s \gtrsim 250 AU ) but becomes quite rapidly anti-correlated with [ Fe/H ] at smaller separations : for 50 < s / { AU } < 100 , the binary fraction at [ Fe / H ] = -1 exceeds that at [ Fe / H ] = 0.5 by a factor of 3 , an anti-correlation almost as strong as that found for close binaries with a < 10 AU .
Interpreted in terms of models where disk fragmentation is more efficient at low [ Fe/H ] , our results suggest that 100 < a / { AU } < 200 is the separation below which a significant fraction of binaries formed via fragmentation of individual gravitationally unstable disks rather than through turbulent core fragmentation .
We provide a public catalog of 8,407 binaries within 200 pc with spectroscopically-determined [ Fe/H ] for at least one component .