Clathration of two-dimensional coordination polymers:: Synthesis and structures of [M(4,4′-bpy)2(H2O)2](ClO4)2•(2,4′-bpy)2•H2O and [Cu(4,4′-bpy)2(H2O)2](ClO4)4•(4,4′-H2Bpy) (M = CdII, ZnII and bpy = bipyridine)

In the presence of guest 2,4'-bpy molecules or under acidic conditions, three compounds, [Cd(4,4'-bpy)(2)(H2O)(2)](ClO4)(2) . (2,4'-bpy)(2) . H2O (1), [Zn(4,4'-bpy)(2)(H2O)(2)](ClO4)(2) .(2,4'-bpy)(2) . H2O (2), and [Cu(4,4'-bpy)(2)(H2O)(2)](ClO4)(4) .(4,4'H(2)bpy) (3), were obtained from the reactions of the metal salts and 4,4'-bpy in an EtOH-H2O mixture. 1 has a 2-D square-grid network structure, crystallizing in the monoclinic space group P2/n, with a = 13.231 (3) Angstrom, b = 11.669(2) Angstrom, 15.019(3) Angstrom, beta = 112.82(3)degrees, Z = 2; 2 is isomorphous with 1, crystallizing in the monoclinic space group P2/n, with a 13.150(3) Angstrom, b = 11.368(2) Angstrom, c = 14.745(3) Angstrom, beta = 110.60(3)degrees Z = 2. The square grids superpose on each other into a channel structure, in which each layer consists of two pairs of shared edges, perfectly square-planar with an M-Pi ion and a 4,4'-bpy at each corner and side, respectively. The square cavity has dimensions of 11.669(2) x 11.788(2) and 11.368(2) x 11.488(2) Angstrom for 1 and 2, respectively. Every two guest 2,4'-bpy molecules are clathrated in each hydrophobic host cavity and are further stabilized by pi-pi stacking and hydrogen bonding interactions. The NMR spectra clearly confirm that both 1 and 2 contain 4,4'-bpy and 2,4'-bpy molecules in a 1:1 ratio, which have stacking interaction with each other in the solution. 3 crystallizes in the orthorhombic space group Ibam, with a 11.1283(5) Angstrom, b = 15.5927(8) Angstrom, 22.3178(11) Angstrom, Z = 4. 3 is made up of two-dimensional square [Cu-4(4,4'-bpy)(4)] grids, where the square cavity has dimensions of 11.13 x 11.16 Angstrom. Each [4,4'-H(2)bpy](2+) cation is clathrated in a square cavity and stacks with one gait of apposite edges of the host square cavity in an offset fashion with the face-to-face distance of ca. 3.95 A. Within each cavity, the [4,4'-H(2)bpy](2+) cation forms twin three-center hydrogen bonds with two pairs of ClO4- anions. The results suggest that the guest 2,4'-bpy molecules and protonated [4,4'-H(2)bpy](2+) cations present in the reaction systems serve as structure-directing templates in the formation of the crystal structures and exclude self-inclusion of the networks having larger square cavities.