Heterometallic Modular Metal–Organic 3D Frameworks Assembled via New Tris-beta-Diketonate Metalloligands: Nanoporous Materials for Anion Exchange and Scaffolding of Selected Anionic Guests

The modular engineering of heterometallic nanoporous metal-organic frameworks (MOFs) based on novel tris-chelate metalloligands, prepared using the functionalised b-diketone 1,3-bis(4’-cyanophenyl)-1,3-propanedione (HL), is described. The complexes [M(III)L3] (M=Fe3+, Co3+) and [M(II)L3](NEt4) (M=Mn2+, Co2+, Zn2+, Cd2+) have been synthesised and characterised, all of which exhibit a distorted octahedral chiral structure. The presence of six exo-oriented cyano donor groups on each complex makes it a suitable building block for networking through interactions with external metal ions. We have prepared two families of MOFs by reacting the metalloligands [M(III)L3] and [M(II)L3]- with many silver salts AgX (X=NO3-, BF4-, PF6-, AsF6-, SbF6-, CF3SO3-, tosylate), specifically the [M(III)L3Ag3]- ACHTUNGTRENUNGX3·Solv and [M(II)L3Ag3]X2·Solv network species. Very interestingly, all of these network species exhibit the same type of 3D structure and crystallise in the same trigonal space group with similar cell parameters, in spite of the different metal ions, ionic charges and X- counteranions of the silver salts. We have also succeeded in synthesising trimetallic species such as [ZnxFeyL3Ag3]-(ClO4)(2x+3y)·Solv and [ZnxCdyL3Ag3]-(ClO4)2·Solv (with x+y=1). All of the frameworks can be described as sixfold interpenetrated pcu nets, considering the Ag+ ions as simple digonal spacers. Each individual net is homochiral, containing only D or L nodes; the whole array contains three nets of type D and three nets of type L. Otherwise, taking into account the presence of weak Ag-C sigma bonds involving the central carbon atoms of the b-diketonate ligands of adjacent nets, the six interpenetrating pcu networks are joined into a unique non-interpenetrated six-connected frame with the rare acs topology. The networks contain large parallel channels of approximate hexagonal-shaped sections that represent 37-48% of the cell volume and include the anions and many guest solvent molecules. The guest solvent molecules can be reversibly removed by thermal activation with retention of the framework structure, which proved to be stable up to about 270°C, as confirmed by TGA and powder XRD monitoring. The anions could be easily exchanged in singlecrystal to single-crystal processes, thereby allowing the insertion of selected anions into the framework channels.