6533b82efe1ef96bd1293359

RESEARCH PRODUCT

Postsynthetic Improvement of the Physical Properties in a Metal-Organic Framework through a Single Crystal to Single Crystal Transmetallation

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As ingle crystal to single crystal transmetallation process takes place in the three-dimensional (3D) metal- organic framework (MOF) of formula Mg II 2{Mg II 4(Cu II 2- (Me3mpba)2)3}·45 H2 O( 1 ;M e 3mpba 4¢ = N,N'-2,4,6-trimethyl- 1,3-phenylenebis(oxamate)). After complete replacement of the Mg II ions within the coordination network and those hosted in the channels by either Co II or Ni II ions, 1 is transmetallated to yield two novel MOFs of formulae Co2 II {Co II 4(Cu II 2(Me3- mpba)2)3}·56 H2 O( 2 )a nd Ni2 II {Ni II 4(Cu II 2(Me3mpba)2)3}· 54 H2 O( 3). This unique postsynthetic metal substitution affords materials with higher structural stability leading to enhanced gas sorption and magnetic properties. The design and synthesis of metal-organic frameworks (MOFs) have experienced ar apid development during the past years. (1) Since the pioneering works on the structural chemistry of MOFs, (2) interest in this field has increased exponentially .I na ddition to the wide range of physical and chemical properties that MOFs can exhibit, (3) this unique class of molecular multifunctional materials provide an excellent playground to study complex supramolecular dynamic pro- cesses. (4) An accurate control of the MOF structure through ligand design is crucial to achieve the desired properties .I nt his sense ,M OFs with predetermined dimensionalities and spe- cific topologies can be designed, to ac ertain extent, by ac areful choice of metal ions and organic ligands .H owever, at otal control of the MOF structure is not always possible because of the many subtle factors that may affect their assembly. (5) Alternative synthetic routes for the synthesis of MOFs with the desired physical properties ,c onsisting of ligand chemical modification and/or metal substitution (trans- metallation) of ap reformed MOF without altering its structure ,a re very promising because of the possibility to better control the nature of the ligand spacers and the interacting metal nodes of the MOF structure. (6) Up to now, only af ew examples showing ac omplete transmetallation within the coordination network of the MOF have been reported, with partial transmetallation within the pores being more frequently observed. (7) This is not surprising considering that controlling selective bond destruction and formation in the solid state has proved challenging. Herein, we report au nique solid-state transmetallation in an ew series of oxamato-based 3D MOFs with two exchange- able metal sites of general formula M II 2{M II 4(Cu II 2-