Cation Exchange in Dynamic 3D Porous Magnets: Improvement of the Physical Properties

We report two novel three-dimensional
porous coordination polymers (PCPs) of formulas Li4{Mn4[Cu2(Me3mpba)2]3}·68H2O (2) and K4{Mn4[Cu2(Me3mpba)2]3}·69H2O (3) obtainedvia alkali
cation exchange in a single-crystal to single-crystal processfrom
the earlier reported anionic manganese­(II)–copper­(II) PCP of
formula Na4{Mn4[Cu2(Me3mpba)2]3}·60H2O (1) [Me3mpba4– = N,N′-2,4,6-trimethyl-1,3-phenylenebis­(oxamate)].
This postsynthetic process succeeds where the direct synthesis in
solution from the corresponding building blocks fails and affords
significantly more robust PCPs with enhanced magnetic properties [long-range
3D magnetic ordering temperatures for the dehydrated phases (1′–3′) of 2.0 (1′), 12.0 (2′), and 20.0 K (3′)]. Changes in the adsorptive properties upon postsynthetic
exchange suggest that the nature, electrostatic properties, mobility,
and location of the cations within the framework are crucial for the
enhanced structural stability. Overall, these results further confirm
the potential of postsynthetic methods (including cation exchange)
to obtain PCPs with novel or enhanced physical properties while maintaining
unaltered their open-framework structures.