3,3 '-Di(pyrazinamoyl)-2,2 '-bipyridine: rational ligand design for the self-assembly of a 1-D coordination polymer

摘要

A new ligand, 3,3'-di(pyrazinamoyl)-2,2'-bipyridine, (LH2)-H-3 has been prepared and is comprised of distinct binding domains capable of facilitating the formation of coordination polymers. Reaction of (LH2)-H-3 with [Cu-2(OAc)(4)(H2O)(2)] in the presence of Et3N center dot HCl affords the complex {[Cu-6(L-3)(2)(Cl)(2)(OAc)(6)]center dot 2H(2)O center dot 2MeOH}(n) (1) in which the [L-3](2-) anion binds two unique copper ions in a bis-tridentate fashion via amide and pyridyl N atoms. This bimetallic unit is linked to an equivalent unit via a pair of 1,3-acetato and mu-chloro bridges to afford a tetrameric [Cu-4(L-3)(2)Cl-2(OAc)(2)] core. Coordination of one of the pyrazole substituents from each ligand to a third copper centre of a rigid paddlewheel [Cu-2(OAc)(4)] unit leads to a unique 1-D polymeric structure. Magnetic studies of 1 reveal that the magnetism can be described in terms of two sets of exchange interactions; strong antiferromagnetic interactions between the two copper centres within the "paddle-wheel" (J/k = -190 K) and a combination of weaker ferro-and antiferro-magnetic interactions within the tetrameric core (J'/k = -5.7 K and J ''/k = +2.1 K).