Enantiomerically Pure Chiral Coordination Polymers:  Synthesis, Spectroscopy, and Electrochemistry in Solution and on Surfaces

Abstract

The two enantiomerically pure bridging ligands (+/-)-[ctpy-x-ctpy] have been prepared employing a two-fold stereospecific alkylation reaction of the enantiomerically pure, chiral terpyridyl-type ligands (+/-)-ctpy. The reaction of each of the enantiomerically pure bridging ligands with Fe(2+) gives rise to chiral coordination polymers whose formation and stoichiometry were followed spectrophotometrically. An assignment of the absolute configuration of the formed helical polymeric structures was carried out on the basis of circular dichroism studies. Highly ordered domains (as determined from STM imaging) of the enantiomerically pure chiral redox polymers could be prepared via the interfacial reaction, over an HOPG substrate, of the bridging ligand in CH(2)Cl(2) and FeSO(4) in water. The degree of polymerization was estimated to be up to 60 from analysis of the STM images of the highly ordered domains on HOPG. The helicality of the domains was compared to the configuration obtained from the circular dichroism studies. The electrochemical properties of the polymers were investigated using cyclic voltammetry and the results compared to those of the respective monomeric complexes. The redox behavior of the iron centers in the polymer was comparable to that of the monomeric complex [Fe((-)-ctpy)(2)](PF(6))(2) as well as to that of [Fe(tpy)(2)](PF(6))(2). The polymeric materials undergo electrodeposition following the two-electron reduction of each bridging ligand unit (one electron per terpyridine group). No ligand-mediated metal-metal interactions were evident from the cyclic voltammetric measurements, suggesting that the metal centers act independently. Moreover, oxidation of the metal centers within the polymeric materials did not give rise to electrodeposition.

New Functional Polymers and Materials Based on 2,2′:6′,2″‐Terpyridine Metal Complexes

“…[69] , already mentioned in Section 1 of this review, were deposited as a monomolecular film on HOPG. [18] As in the case of the dendrimeric system mentioned above, CV measurements proved the adsorption of a bis-terpyridine±Fe II complex containing species. STM images of films derived from each of the metal± enantiomeric ligand complexes showed mirror symmetric structures.…”

“…4). [18] Complexation reactions with iron(II) salts were studied in solution with UV/vis and CD spectroscopy, in order to confirm the formation of chiral metallo-assemblies. From the UV/vis titration with iron(II) tetrafluoroborate it can be seen that the isolated MLCT band especially increases in intensity up to an equivalent of 1:1, but remains unchanged after overtitration (Fig.…”

Chiral Heterocyclic Ligands. XI. Self-assembly and X-ray Crystal Structures of Chiral Silver Coordination Polymers of (S)-(–)-Nicotine

“…Various approaches have been employed in the design of homochiral coordination polymers. These include the use of chiral metal precursors [28], chiral ligands [29][30][31][32][33][34], chiral counterions [35,36], helicate formation [37][38][39][40][41] and even the use of spontaneous resolution of achiral materials [42][43][44][45].…”

“…Various approaches have been employed in the design of homochiral coordination polymers. These include the use of chiral metal precursors [28], chiral ligands [29][30][31][32][33][34], chiral counterions [35,36], helicate formation [37][38][39][40][41] and even the use of spontaneous resolution of achiral materials [42][43][44][45].We believe that the simplest approach is to use chiral bridging ligands and have recently reported the synthesis and study of some C 2 -symmetric chiral bridging ligands derived from the readily available monoterpene (+)-camphor [46,47] Crystalline products suitable for X-ray structure determination were obtained from three such reactions. Reaction of equimolar quantities of silver nitrate and nicotine in acetonitrile followed by vapour diffusion of diethyl ether into the reaction mixture furnished a crystalline product (2) that was shown by elemental analysis to have a 1:1 metal:ligand ratio.…”

Spontaneous chiral resolution directed by symmetry restriction and π-π interaction

“…Metal-organic frameworks (MOFs), an important class of self-assembled materials, built by organic linkers and metal ions or clusters have attracted great attention over the past decades due to the structural diversity and outstanding properties67891011121314151617181920. Chiral MOFs are more attractive because of their additional properties for asymmetric catalysis, entiomorphous selectivity, chiral molecular imaging, etc1415161718.…”