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 [Zn3(OAc)6(HL 1)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)].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].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-HCl hydrogen bonds. The nitrates of zinc(ii), cobalt(ii) and nickel(ii) react with 3,5-di(3-pyridyl)-1H-pyrazole (HL 2) to form [M(MeOH)4(HL2)2](NO 3)2.2H2O (5, M = Zn; 6, M = Co; 7, M = Ni). These isostructural compounds contain discrete cations that are linked into double-stranded chains by O-HN 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. Copyright 2011 The Royal Society of Chemistry
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