Acid directed in situ oxidation and decarboxylation of 4,4′,6,6′-tetra-methyl-2,2′-bipyridine: Synthesis and structural characterisation of 4,4′,6-tri-carboxy-2,2′-bipyridine and its copper(II) coordination polymer
作者:Niamh R. Kelly、Sandrine Goetz、Chris S. Hawes、Paul E. Kruger
DOI:10.1016/j.ica.2012.12.033
日期:2013.7
The reaction of either 4,4',6,6'-tetramethyl-2,2'-bipyridine, L, or 4,4',6,6'-tetracarboxy-2,2'-bipyridine, H4L, with Cu(OAc)(2)center dot H2O under acidic hydrothermal conditions (50:1 H2O/HNO3; 160 degrees C) led to the formation of crystalline [Cu(HL')(H2O)]center dot H2O}, 1, which was structurally characterised to identify H3L' as 4,4',6-tricarboxy-2,2'-bipyridine. Clearly, in situ mono-decarboxylation of a tetracarboxylic acid ligand gave the tricarboxy-analogue, H3L'. The structure of 1 consists of a 1D coordination polymer that cross-links through hydrogen-bonding between adjacent carboxylic acid and carboxylate groups, as well as through an aqua ligand and lattice water molecule, to form a densely interconnected 3D network. Regioselective mono-decarboxylation of L or H4L at the 6'-carboxylic acid position may also be affected by heating L or H4L in acidic solution under hydrothermal conditions (2:1 H2O/HNO3; 160 degrees C) to yield crystalline 4,4',6'-tricarboxy-2,2'-bipyridinium nitrate hydrate [H4L'][NO3]center dot H2O}, 2, which was also structural characterised. The structure of 2 features an array of hydrogen-bonding interactions that generate a 3D network. More forceful heating of the acidic solution at 180 degrees C led to double decarboxylation and the formation of 4,4'-dicarboxy-2,2'-bipyridine, whereas heating at 200 degrees C led to total decarboxylation and the formation of 2,2'-bipyridine. Details of the structures of 1 and 2 along with their synthesis are discussed. (C) 2012 Elsevier B. V. All rights reserved.