Competition between coordination and hydrogen bonding in networks constructed using dipyridyl-1H-pyrazole ligands

The reaction between zinc(II) acetate and 3,5-di(4-pyridyl)-1H-pyrazole (HL1) is crucially dependent on the solvent, with products based on different architectures formed in DMF, methanol and water. When the reaction is undertaken in DMF, the product is [Zn-3(OAc)(6)(HL1)(4)] 1, in which Zn(OAc)(2) centres link Zn-2(OAc)(4)(HL1)(4) units into double-stranded zig-zag chains. Each chain is 'broken' after every fourth HL1 ligand, though the links between the chains ensure a coordination polymer is formed. The reaction in methanol produces [Zn(OAc)(2)(HL1)]center dot 0.5MeOH 2 which also contains double-stranded chains, though in this case both chains are continuous. The hydrothermal reaction gives [Zn(OAc)(2)(HL1)(2)]center dot H2O 3, which contains discrete zinc complex molecules that are linked into double-stranded chains through hydrogen bonds. Zinc(II) chloride reacts with HL1 to form [ZnCl2(L-1)] 4. The structure of 4 consists of chains that are cross-linked into sheets by N-H center dot center dot center dot Cl hydrogen bonds. The nitrates of zinc(II), cobalt(II) and nickel(II) react with 3,5-di(3-pyridyl)-1H-pyrazole (HL2) to form [M(MeOH)(4)(HL2)(2)](NO3)(2)center dot 2H(2)O (5, M = Zn; 6, M = Co; 7, M = Ni). These isostructural compounds contain discrete cations that are linked into double-stranded chains by O-H center dot center dot center dot N hydrogen bonds, with further hydrogen bonds connecting these into sheets. The structures of 1-3 and 5-7 all contain double-stranded chains, with both bridging ligands and hydrogen bonds linking individual chains into pairs.