Abstract: A crystalline sorbent material of formula: AbM?[M(CN)6]y·nH2O wherein A is a group 1 metal; b is from 0.001 to 0.3; M? is a transition metal; M is iron or cobalt; y is from 0.65 to 0.80; and n is from 0 to 7. The crystalline sorbent materials of the present invention may be used in a method of capturing water. The method of the present invention utilising such crystalline sorbent materials may be used in water capture and purification processes to provide fresh water suitable for drinking or for use in agriculture. The method of the present invention may also be used to remove water as a contaminant or for use in dehumidification processes. A use of such a crystalline sorbent material is also disclosed.