Acyclic and cyclic compartmental ligands: Recent results and perspectives

The most relevant results published from 2006 up to 2010 are reported; they especially regard the synthetic pathway and the structural and physico-chemical aspects of planar or tridimensional cyclic and acyclic compartmental Schiff bases, their polyamine homologs and related polynuclear complexes. Particular emphasis is placed on the role of the shape of the coordinating ligands and of the different metal ions in directing the synthesis totally or preferentially toward specific entities. The multiple self-condensation of appropriately designed polyformyl- with polyamine-precursors or the templating capability of different metal ions in directing the synthesis pathway toward specific compounds are evaluated together with the possibilities offered by the transmetalation reactions in the obtainment of not otherwise accessible complexes. The ability of compartmental ligands to bind two or more metal ions in close proximity into two identical or different compartments, the presence of different bridging groups inside these coordination moieties, the insertion of peripheral functionalities and their relevance in modulating the type and the extent of mutual interaction between the metal ions inside the adjacent chambers and in producing quite sophisticated architectures is reviewed. The selective generation of helically folden strands, which can modify their structure into a linear one upon complexation and to return to the helical form by demetalation cycling between contracted and extended structures, is also reported. Also the ability of acyclic and macrocyclic ligands without endogenous bridging groups to incapsulate two or more metal ions and to act as building blocks in the construction of oligomeric or polymeric systems is also analyzed. The magneto-structural correlation of the homo- and hetero-dinuclear or -polynuclear complexes, together with the photochemical and photophysical properties resulting from these specific recognition processes, were also considered. The insertion of specific linkers. capable of evolving dinuclear complexes into oligomeric or polymeric ones or into unusual structures with the consequent modification of their properties, is also reported. Also, the design and diversification of the two adjacent sites, aimed at enhancing the ability of these ligands to act as selective transfers of specific cations, anions or salts across liquid membranes are discussed. Finally, the specific reactivity and catalytic properties arising from di- or polynuclear aggregations are considered. (C) 2012 Elsevier B.V. All rights reserved.