Alkali metal cation effects on hydrogen uptake and binding in metal-organic frameworks.

A 2-fold interwoven metal-organic framework has been chemically reduced and doped with Li(+), Na(+), and K(+). At low pressures and temperatures, the reduced and doped materials exhibit enhanced H2 uptakeup to 65% higher than for the neutral framework. Notably, at similar doping levels, H2 binding is strongest with Li(+) and decreases as Li(+) > Na(+) > K(+). However, the uptake increases in the opposite order. We attribute the behavior to structural changes accompanying framework reduction.