Hydrogen peroxide can still form adducts with very strong acids.

Hydrogen peroxide is a much weaker Base (chemistry) than water, but it can still form adducts with very strong acids.

Square planar complexes of nickel can often form five-coordinate adducts.

This complex is a Lewis acid and forming adducts with a variety of hard bases.

For example, it forms stable adducts with metallocenes.

They form adducts with other (acidic) fluorides through their lone pair.

For example it reversibly forms adducts with some pharmaceuticals.

It forms adducts with a variety of Lewis bases.

It is a weak Lewis acid, forming adducts with pyridine and methylamine.

Others solids form adducts with other gases, (for example CO or ethylene).