Non‐Natural Eight‐Connected Solid‐State Materials: A New Coordination Chemistry

Abstract

Molecular and materials science has provided a wide range of topologies and connectivities in the solid state. The most common nomenclature for such systems has been based [1][2][3] on the idea of two-, three-, four-, or six-connected materials in one, two and three dimensions. [4][5][6][7][8][9][10][11] Connectivities of five, seven, or higher are extremely rare, [12][13][14] and recent studies on inorganic/organic hybrid materials, especially in the area of metal-ligand coordination framework polymers, have enriched this area substantially. [15][16][17][18][19][20][21] However, highly connected materials remain scarce because the construction of such systems is severely hampered by the available number of coordination sites at the metal centers and the sterically demanding nature of organic ligands. Our design is based upon the combination of high coordination number lanthanide metal centers and 4,4'-bipyridine-N,N'-dioxide ligands. The latter have flexible angular geometries at the O-donor, are complementary to hard lanthanide metal centers, and, therefore, form highly stable yet sterically flexible complex geometries. The only previously known examples of eightconnected frameworks have body-centered-cubic structures, [22][23][24] this structure representing the archetypal textbook lattice as found in CsCl. We report herein three unprecedented and unpredicted eight-connected networks that, for the first time, define non-CsCl topologies for eight-connected solid-state materials.The compounds 1-3 have been obtained by slow diffusion of methanolic solutions of La(CF 3 SO 3 ) 3 , La(ClO 4 ) 3 , or Yb(CF 3 SO 3 ) 3 , respectively, and 4,4'-bipyridine-N,N'-dioxide (L) in MeOH in a U-tube through a buffering layer of CH 2 Cl 2 (for 1), CHCl 2 CHCl 2 (for 2), or C 2 Cl 4 (for 3). Compound 3 can also be prepared by covering the solid metal salt Yb(CF 3 SO 3 ) 3 with CH 2 Cl 2 or chlorobenzene and carefully layering with a solution of L in MeOH. Single-crystal X-ray structure determinations [25] of 1-3 confirm that they all have polymeric structures based on networks of eight-coordinated Ln III nodes linked by bridging L ligands. The asymmetric unit of 1 contains two independent La III centers. Although both are eight-coordinate, their coordination spheres are different. One La III center is bound by eight molecules of L, each bridging between the metal center and eight other La III centers. This, therefore, defines an eightconnected node within the structure. The second Ln III center is ligated with a molecule of MeOH and seven molecules of L with each of the latter bridging to seven other Ln III ions. This, therefore, defines a seven-connected node. At each metal center, four of the bridging ligands are used to generate a (4,4) net in which the remaining ligands are sited on the same side of the net linking to a second (4,4) net to give the observed bilayer motif. This affords three-and fourfold bridges from seven-and eight-connected centers, respectively, between the two (4,4) nets (Figure 1) with a tetragonal antipr...

Self-assembly as a route to dinuclear lanthanide complexes with rare coordination pattern of salen-type ligand

“…Compared with d-electron elements, the potential of lanthanide ions in the rational design and synthesis of well-defined supramolecular architectures has been less exploited due to the difficulty in controlling the coordination environments of these ions which display high and variable coordination numbers with little stereochemical preferences. Many interesting supramolecular structures involving the lanthanides are sometimes unexpected and cannot be predicted [9][10][11][12][13][14][15][16]. However, their retrospective analysis may provide necessary information in the attempts at intentional design of new materials with specific functions and properties.…”

An unusual 3D complex showing 5,8-connected topology with encapsulated 8-connected octamolybdate polyoxoanions

“…Till now, many examples of highly connected coordination frameworks have been observed [50][51][52][53][54], however, 5,8-connected networks remains a challenging issue in coordination chemistry. The reason for this is due to that the triangular bipyramid coordination geometry is very rare for most of the transition metal ions.…”

An unusual binodal (6,8)-connected 3D supramolecular network with twofold self-penetration

“…Examples of five-, seven-, and eight-connected MOFs are relatively scarce [7,10,11]. To design such high-connected MOFs, the concept of secondary building units (SBUs) is utilized because these SBUs generally possess larger sizes, more coordination sites, and smaller steric hindrance for ligands [12][13][14][15].…”