Date: 19 Jul 2011

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

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Abstract

The synthesis and crystal structures of three new metal organic frameworks of type [Zn(L-2H)] n (1), {[ZnLCl2](CH3CN)0.5(DMF)0.5(H2O)0.5} n (2) and {[CdL(DMF)(NO3)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)(ClO4)] n (4). In [Zn(L-2H)] n , the zinc ion occupies the macrocyclic cavity, being bound to the N4-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 {[ZnLCl2](CH3CN)0.5(DMF)0.5(H2O)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)(NO3)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)(ClO4)] 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.

Andrew Parkin—deceased.
Y. Mulyana, C. J. Kepert, J. McMurtrie, P. Turner, G. Wei and J. G. Wilson dedicate this manuscript to Prof. Len Lindoy in celebration of his 75th birthday.