552272-75-0Relevant academic research and scientific papers
Stereoselective association of binuclear metallacycles in coordination polymers
Khlobystov, Andrei N.,Brett, Matthew T.,Blake, Alexander J.,Champness, Neil R.,Gill, Peter M. W.,O'Neill, Darragh P.,Teat, Simon J.,Wilson, Claire,Schroeder, Martin
, p. 6753 - 6761 (2007/10/03)
A series of structurally related binuclear metallacycles Cd(NO3)2L]2, where L is an angular exobidentate ligand, have been synthesized. Each metallacycle contains two coordinatively unsaturated, chiral metal centers within a single molecule, and the assembly of these metallacycles into polymeric framework structures has been studied systematically for the first time. Stereoselective homochiral association of [Cd(NO3)2L]2 leads to the formation of helical coordination polymers, whereas meso type association results in nonhelical chain structures. The type of stereoselective aggregation depends on the conditions of self-assembly as well as on ligand functionality. Both helical and nonhelical polymeric complexes have been isolated for the metallacycle [Cd(NO3)2(2,4′-pyacph)]2 (2,4′-pyacph = 2,4′-(4-ethynylphenyl)bipyridyl). Homochiral association results in the formation of helical [Cd(NO3)]∞ chains which link the binuclear [Cd(NO3)2(2,4′-pyacph)]2 metallacycles into racemic two-dimensional sheets which contain both P and M [Cd(NO3)]∞ helices. In contrast, meso-association leads to the formation of nonhelical one-dimensional chains. It is shown that the product of homochiral association is predominately formed at room temperature and that of meso-association is generated at elevated temperatures. Thus, it may be concluded that the homochiral association appears to be energetically less favorable than the meso-association, a conclusion that has been confirmed by theoretical calculations of the crystal lattice energy. Several high-yield syntheses of bipyridyl-type ligands used for metallacyclic assembly are also reported.
