New metal–organic frameworks and supramolecular arrays assembled with the bent ditopic ligand 4,4-diaminodiphenylmethane

Abstract

Twelve novel coordination polymers and supramolecular architectures have been obtained using the bent ditopic ligand 4,4′-diaminodiphenylmethane (dadpm) and different metal salts (chlorides and nitrates), and their structures have been elucidated by single crystal X-ray analysis. The new products include some examples of simple zigzag chains, as in [MCl₂(dadpm)] [M = Co (1); M = Cd (2)] and [Ag(NO₃)(dadpm)] (3). The chains are connected via weaker interactions (H-bonds or contacts with the anions) to give 2-D layers. In [Ni(H₂O)₂(dadpm)₂]Cl₂ (4) the polymeric 1-D chains consist of parallel ribbons of rings with the non-coordinated chloride anions generating a 3-D architecture via NH⋯Cl bonds. Noteworthy, compound 5a, [Ni(H₂O)₂Cl₂(dadpm)₂], has an identical composition but a different structure, thus representing a novel case of supramolecular isomerism: it contains mononuclear octahedral complexes, with two trans coordinated H₂O molecules, two trans Cl anions and two trans monodentate dadpm ligands. The dangling ends of the dadpm ligands, however, form H-bonds with the H₂O molecules coordinated on adjacent complexes, thus giving rise to double-stranded chains resembling the ribbons of rings present in 4. Compound 5b, [Mn(H₂O)₂Cl₂(dadpm)₂], is isomorphous with 5a and also compound 6, [Ni(H₂O)₂(NO₃)₂(dadpm)₂], shows a similar structure. Compounds [MCl₂(dadpm)] [M = Cd (7); M = Mn (8)] are isostructural, but not isomorphous, and contain single 3-D networks with the ths (ThSi₂) topology. In compound 9, [CdCl₂(dadpm)], complex 2-D layers of (6,3) topology are observed. The structure of [Cd₃Cl₆(dadpm)₂] (10) is comprised of complex Cd/Cl chains inter-connected by double bridging dadpm ligands to give a 3-D network with the cds (CdSO₄) topology (or, alternatively, the cds-a augmented topology). In [Ag(dadpm)₃](NO₃) (11) the Ag centres are octahedrally coordinated by six bridging dadpm ligands, resulting in a 3-D network with the pcu (α-Po) topology. It is worth mentioning that three compounds (2, 7 and 9, of composition [CdCl₂(dadpm)]) show a remarkable case of supramolecular isomerism.