Dehydration of the nanoporous coordination framework ErIII[CoIII(CN)6].4(H2O): single crystal to single crystal transformation and negative thermal expansion in ErIII[CoIII(CN)6].

Desorption of bound and unbound water molecules from the nanoporous coordination framework ErIII[CoIII(CN)6].4(H2O) to form the apohost, ErIII[CoIII(CN)6], proceeds via a single crystal to single crystal transformation in which the Er(III) cations change from 8- to 6-coordinate; dehydration results in a striking change in the thermal expansion properties.