Coordination polymers that afford controllable cavities and incorporate different guest molecules may provide structural prototypes for the design of porous host lattices for applications such as adsorption, [1,2] ion exchange [3] and heterogeneous catalysis. [4] The elaboration of such materials is a considerable challenge, as only a few of the previously synthesized solids are stable to the loss of the initially accumulated guests and capable of taking up small organic molecules in the resulting molecular holes. [1] New insights into the development of approaches for the engineering of metal-organic zeolites are possible on the basis of topological considerations. [5] Attractive metal-organic-zeolite models of metal-organic frameworks may be predicted for novel "2D building blocks" of semiregular topology [6] (Figure 1 b and c) that are expanded in a third direction by pillaring. [7] In this case, initial plane tiling by a set of different polygons, instead of uniform square grids as in [Cu(bipy) 2 SiF 6 ], [2] generates closely packed molecular triangles (cf. molecular hexagons) with very open regions within the network. Thus, the free space appears to be concentrated, and the resulting framework of relatively low overall porosity, which is stable and robust, could maintain large cages for guest molecules. Realistic prototypes of such arrays are provided by the structures of purely inorganic materials-tungsten bronzes. [6b] Herein, we report how the combination of the inherent functional features of organic and inorganic counterparts allows an especially effective implementation of this assembly scenario, and the generation of a target coordination network with unprecedented hexagonal tungsten bronze topology. Despite the fact that the angles at the net vertex (2 60, 2 1208) do not match the demands of a typical coordination environment around octahedrally coordinated transitionmetal ions, the desired connectivity may be tuned by the conformational flexibility of the organic linker. First, the 3,3',5,5'-tetramethylsubstituted 4,4'-bipyrazolyl ligand (4,4'-bpz) acts as an angular linker. [8] Its frame includes two planar pyrazolyl fragments, which have an angle of rotation around 60-808 and the resulting noncollinear orientation of two NÀM vectors makes possible the assembly of the desired flat coordination net. Second, these coordination layers [M(4,4'-bpz) 2 ] n , formed by the octahedrally coordinated metal ions and two equivalents of the bridging 4,4'-bpz ligands, have a rich and versatile functionality for cross-linking into a 3D superstructure. Each four-coordinate point M(pyrazole) 4 of the layer provides, in the two axial directions, six binding sites that include coordination positions at the metal atom, and four hydrogen bond donating NH groups of the coordinated pyrazole ligands. Thus, dense interconnection of the layers and generation of a rigid 3D network is feasible by the rational choice of an anionic counterpart to fit perfectly this set of binding sites.The 3D structure of a new family of fr...
Coordination polymers that afford controllable cavities and incorporate different guest molecules may provide structural prototypes for the design of porous host lattices for applications such as adsorption, [1,2] ion exchange [3] and heterogeneous catalysis.[4] The elaboration of such materials is a considerable challenge, as only a few of the previously synthesized solids are stable to the loss of the initially accumulated guests and capable of taking up small organic molecules in the resulting molecular holes.[1] New insights into the development of approaches for the engineering of metal-organic zeolites are possible on the basis of topological considerations.[5] Attractive metal-organic-zeolite models of metal-organic frameworks may be predicted for novel "2D building blocks" of semiregular topology [6] ( Figure 1 b and c) that are expanded in a third direction by pillaring. [7] In this case, initial plane tiling by a set of different polygons, instead of uniform square grids as in [Cu(bipy) 2 SiF 6 ], [2] generates closely packed molecular triangles (cf. molecular hexagons) with very open regions within the network. Thus, the free space appears to be concentrated, and the resulting framework of relatively low overall porosity, which is stable and robust, could maintain large cages for guest molecules. Realistic prototypes of such arrays are provided by the structures of purely inorganic materials-tungsten bronzes.[6b]Herein, we report how the combination of the inherent functional features of organic and inorganic counterparts allows an especially effective implementation of this assembly scenario, and the generation of a target coordination network with unprecedented hexagonal tungsten bronze topology. Despite the fact that the angles at the net vertex (2 60, 2 1208) do not match the demands of a typical coordination environment around octahedrally coordinated transitionmetal ions, the desired connectivity may be tuned by the conformational flexibility of the organic linker. First, the 3,3',5,5'-tetramethylsubstituted 4,4'-bipyrazolyl ligand (4,4'-bpz) acts as an angular linker.[8] Its frame includes two planar pyrazolyl fragments, which have an angle of rotation around 60-808 and the resulting noncollinear orientation of two NÀM vectors makes possible the assembly of the desired flat coordination net. Second, these coordination layers [M(4,4'-bpz) 2 ] n , formed by the octahedrally coordinated metal ions and two equivalents of the bridging 4,4'-bpz ligands, have a rich and versatile functionality for cross-linking into a 3D superstructure. Each four-coordinate point M(pyrazole) 4 of the layer provides, in the two axial directions, six binding sites that include coordination positions at the metal atom, and four hydrogen bond donating NH groups of the coordinated pyrazole ligands. Thus, dense interconnection of the layers and generation of a rigid 3D network is feasible by the rational choice of an anionic counterpart to fit perfectly this set of binding sites.The 3D structure of a new family of framework ...
Cross-linking of corrugated square grid coordination layers by anionic bridging groups generates five-connected coordination networks; the 3D topologies of mixed-anion cobalt(II) and nickel(II) complexes with a tetramethyl-substituted 4,4'-bipyrazolyl ligand are supported by mu-SO4(2-) functions and exist as neutral or cationic five-connected arrays involving additional terminal (NCS-) or non-coordinated (NO3-, ClO4-) groups.
Copper(II) oxalate coordination polymer [{Cu4(C2O4)4(L)4}3 · {Cu3(C2O4)3(L)6}2 · 3L · 25H2O]n (L = 3,3′,5,5′‐tetramethyl‐4,4′‐bipyrazole) reveals a structure that is related to the Pt3O4 net topology. The 3D linkage is sustained with copper‐oxalate squares and copper‐bipyrazole triangles sharing vertices. The framework supports giant icosahedral cages and entraps discrete molecular octahedra formed by two molecular complexes Cu3(C2O4)3(L)6 associated by means of NH‐‐‐N hydrogen bonding. The coexistence of the discrete and 3D portions formed by the same components suggests self‐templation as a key feature of the system. Simpler copper oxalate compounds [Cu(C2O4)(L)2(H2O)] · CH3OH · 3.75H2O and [Cu2(C2O4)2(L)5] · L · 11H2O are concomitant products of the reaction mixture and they exist in the form of molecular mono‐ and binuclear complexes.
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