New metal organic frameworks incorporating the ditopic macrocyclic ligand dipyridyldibenzotetraaza[14]annulene

Abstract

The synthesis and crystal structures of three new metal organic frameworks of type [Zn(L-2H)] n (1), {[ZnLCl 2](CH 3CN) 0.5(DMF) 0.5(H 2O) 0.5} n (2) and {[CdL(DMF)(NO 3) 2]•DMF} n (3), all based on the dipyridyl-derivatised macrocycle, dipyridyldibenzotetraaza[14] annulene (L), are reported along with the X-ray structure of the protonated metal-free ligand as its perchlorate salt, [(HL)(ClO 4)] n (4). In [Zn(L-2H)] n, the zinc ion occupies the macrocyclic cavity, being bound to the N 4-donor set of the macrocyclic ring in its doubly deprotonated form. Each zinc atom is also axially bound by a pyridyl moiety from an adjacent complex, resulting in formation of an infinite one-dimensional chain of the 'herringbone' type in which pairs of macrocyclic complexes interact via face-to-face π-π stacking interactions. In contrast, the zinc ion in {[ZnLCl 2](CH 3CN) 0.5(DMF) 0.5(H 2O) 0.5} n does not occupy the macrocyclic cavity but is bound to a pyridyl nitrogen from two ligands such that it acts as a bridge between macrocyclic units and results in the generation of a one-dimensional chain. Two chloro ligands also bind to each zinc centre to yield a distorted tetrahedral coordination geometry. Offset π-π stacking occurs between adjacent chains involving alternate macrocycles in each chain, giving rise to a zig-zag arrangement. Pairs of interacting chains pass through the above-mentioned chains to generate further π-π stacking to yield an overall three-dimensional structure that contains large ellipsoidal-shaped channels. In {[CdL(DMF)(NO 3) 2]•DMF} n the cadmium ion again does not occupy the macrocyclic cavity but acts as a bridge between macrocycles to once again afford a linear chain structure. Each cadmium is bound to two pyridyl groups (arising from different molecules of L), two nitrato ligands and one oxygen-bound dimethylformamide molecule to yield a distorted pentagonal bipyramidal coordination geometry. The protonated ligand, [(HL)(ClO 4)] n, adopts a linear chain structure in which one pyridyl group is protonated and interacts intermolecularly via a hydrogen bond with the non-protonated pyridyl group of an adjacent macrocyclic unit to yield a hydrogen-bonded linear chain structure. © 2011 Springer Science+Business Media B.V.