ABSTRACT:The two-dimensional structure described here is the first example of a coordination polymer structure consisting of onedimensional polycatenanes fused via silver ions. It can be derived from simple rings consisting of two silver ions and two ligand molecules.In the past decade, metal-organic frameworks (MOFs) have turned out to be a fascinating pool for structure design, synthesis, and applications in numerous fields such as catalysis, magnetism, luminescence, or gas storage. 1 By judicious choice of the building units, (i) the ligand concerning rigidity, form, and donor functions and (ii) the metal ion with its capacity to accept coordination by a given number of ligands, low-dimensional frameworks can be designed and constructed. 2 However, polymorphism and supramolecular isomerism occur more frequently the more flexible both building blocks are. 3 Porous frameworks with large empty spaces are a big challenge as interpenetration can occur. 4 We are interested in using a flexible system with a metal ion such as Ag + and a multitopic ligand Ln (n ) 1, 2 ...) (Scheme 1) with N-and O-donor atoms to synthesize adaptable MOFs, which are able to link a second metal ion type. With the shorter ligand L1, n ) 1, a number of one-dimensional (1D) structural motifs could be characterized, 5-7 whereas with L2, a zero-dimensional metallacycle with two Ag + ions and two L2 molecules, as well as a 1D helix, could be reported. 8 Whereas with this ligand type Ln and Ag + , only coordination numbers of two for Ag + with respect to the nitrogen atoms of Ln were reported so far; 6-9 we now report a new type of network derived from the polycatenation of a 1D chain of fused metallacycles in which Ag + has a coordination number of four with respect to L2. The obtained structure is an unprecedented example of linked polycatenane chains to give a very robust two-dimensional (2D) network of high density.Results and Discussion. The reaction of L2 with AgClO 4 in the ratio 1:1 yields the 2:2 metallacycle or a 1D helix as a supramolecular isomer. 8 With AgPF 6 , exo-linked 2:2 metallacycles of the composition [Ag(L2)] 2 (PF 6 ) 2 ‚THF (1) (THF ) tetrahydrofuran) are obtained. The ratio L2/Ag + of 2:1 yields, after a long reaction time of over two months, a very dense and highly catenated structure of composition [Ag(L2) 2 ](PF 6 ) (2) representing a missing link in polycatenation motifs.1 crystallizes in the triclinic space group P1 h (No. 2), 15 with one molecule per unit cell. Two ligands L2 adopt a U-shape and coordinate to two metal ions to yield a cyclic structure, with Ag-N distances of 2.136(4) and 2.143(4) Å, and an N1-Ag-N2 angle of 169.31(19)° (Figure 1). The two PF 6 -anions bridge two silver ions belonging to the same ring; the Ag-F bonds are weak with distances of 2.960(7) and 3.092(5) Å. Because of this arrangement, the Ag-Ag distance within the ring is rather long at 5.213(13) Å, and π-stacking within the ring is thus excluded with pyridine rings offset from each other by 5.1218 Å.The rings in 1 are arranged parallel...