Cracking occurs because of inhomogeneous shrinkage. Do you materials shrink much ?

This can be reduced by solvent exchange, replacing water in the porosity by diethyl ether for example, having much lower surface tension. The drying must also be slow, for example in an almost cosed vessel. You can also replace water by tert-butanol and freeze-dry your sample. More examples can be found in my RG profile.

Alain

Thanks a lot for the info.

Did you try to make the reaction at a lower temperature?