Anion-controlled assembly of silver(I) complexes of multiring heterocyclic ligands: A structural and photophysical study

• Main Authors: Kundu, N., Audhya, A., Abtab, S.M.T., Ghosh, S., Tiekink, E.R.T., Chaudhury, M.
• Format: Article
• Published: American Chemical Society 2010
• Subjects: QD Chemistry
• Online Access: http://eprints.um.edu.my/15123/

Four multiring heterocyclic ligands with benzimidazole (L-1 and L-3) and benzothiazole nuclei (L-2 and L-4) are reported. Their silver(I) complexes involving it variety of anions (both organic and inorganic) have been prepared by the process of self-assembly and structurally characterized by single-crystal X-ray diffraction analyses. Discrete metallocyclic complexes [Ag(L-3)(X)](2) (X = NO3-, 3a; cis-HOOCCH=CHCOO-, 3b; 0.5SiF(6)(2-) 3c) and [Ag(L-4)(Y)](2) (Y = NO3-, 4a; CF3SO3-, 4b) have been formed with the ligands L-3 and L-4, respectively, where the pyridine nitrogen atom N1 is in the 3-position its against the coordination polymers [Ag(L-1)(H2O)(NO3)](n), 1a, [Ag(L-1)(CF3COO)](n), 1b and {2[Ag(L-2)(2)(ClO4)].0.5.C2H5OH}(n) 2a, and [Ag(L-2)(2)(cis-HOOCCH =CH COO)](n), 2b, with the ligands L-1 and L-2, respectively, in which the N1 atom occupies the 4-position in the pyridine ring. In addition to the primary ligands (L-1-L-4), the counteranions also have it dominant influence on the overall structures of these compounds. Secondary bonding interactions, namely, hydrogen bonding, pi center dot center dot center dot pi-stacking, and C-H center dot center dot center dot pi interactions, are also proven effective in shaping the dimensionalities of the solid state structures. Thus, it zigzag chain structure of 1a mediated by it nitrate anion generates it more complicated double layer structure in 1b where trifluoroacetate has replaced nitrate as the counterion. Discrete 12-membered metallocycles in 3a-3c generate 2-D arrays of flat (3a) and undulating topologies (3b and 3c), depending upon the type of their associated anions. Metallocycles 4a and 4b have less complicated structures compared to those of 3a-3c because of the replacement of NH by S in the heterocyclic ring, thereby reducing the hydrogen-bonding potential in the primary ligand in going from L-3 to L-4. In the solid state, the complexes show enhanced phosphorescence at 77 K with triplet lifetime in the range of 0.5-0.8 s, much shorter than those for the free ligands (2.3 - 3.3 s) because of increased spin-orbit coupling introduced by the coordinated Ag+ ion. This heavy-atom effect also has a causative influence in shortening the fluorescence lifetimes of these compounds.