Zipped-Up Chain-Type Coordination Polymers: Unsymmetrical Amide-Containing Ligands Inducing P-Sheet or Helical Structures

The crystal structures of thirteen Ag-1 coordination polymers involving py-CONH-(CH2)(n)-py (py = pyridine: n=0, 1) derivatives were determined by means of single-crystal X-ray analyses. All of the compounds form one-dimensional chains composed of Ag-1 atoms and bridging ligands with formulas {[Ag(py-CONH-(CH2)(n)-py)] [X]}(n) (X=PF6-, ClO4-, BF4-, and NO3- with solvent molecules). The unsymmetrical coordination environments around Ag-1 atoms induce direction in the chains. that is, -[NH-(CH2)(n)-py-Ag-py-CO]-. which resembles the alignment of amino acid chains in proteins. In compounds {[Ag(4-pia)][X]}(n) (1 superset of X: 4-pia= N-(4-pyridyl)isonicotinamide; X=PF6-, ClO4-, BF4-, and NO3-), {[Ag(4-pmia)][X]}(n) (2 superset of X; 4-pmia=N-(pyridin-4-ylmethyl)isonicotinaniide; X=PF6-, ClO4-center dot H2O, and NO3-center dot H2O and {[Ag(3-pmia)][X]}(n) (3 superset of X; 3-pmia =N-(pyridin-3-ylmethyl)isonicotinamide; X=PF6-, ClO4-, BF4-, and NO3-center dot H2O), each chain is aligned parallel to neighboring chains, but adjacent chains run in the opposite direction. Particularly in {[Ag(3-pmia)]-[PF6]}(n) (3 superset of PF6-), {[Ag(3-pmia)][ClO4]}(n) (3 superset of ClO4-), and {[Ag(3-pmia)][BF4]}(n) (3 superset of BF4-), amide moieties of 3-pmia ligands are complementarily hydrogen bonded to amide moieties in neighboring chains, as in the beta-sheet motif in proteins. On the other hand, in {[Ag(4-pmna)][PF6]center dot MeOH}(n) (4-pmna = N-(pyridin-4-ylmethyl)nicotinamide), all chains in the crystal form left-handed (4a superset of PF6-center dot MeOH) and right-handed (4b superset of PF6-center dot MeOH) helical structures with a helical pitch of 28 angstrom. Heterogeneous anion exchanges proceed reversibly in 2, but not in 3, which provides information about the thermal stabilities of the crystals.