Structural characteristics of some metallo-organic discogens

Abstract

We have recently analysed the crystal and molecular structures of six metalloorganic discogens with substituted β -diketone ligands. The molecules consist of a rigid 11 atom core and a fringe made up of four phenyl rings substituted with alkyl/alkoxy chains. In complex (i), with four octyloxy chains, there are four oxygen atoms around the core. Complex (ii) is asymmetrically substituted with two heptyloxy and two heptyl chains and therefore has two oxygen atoms and complexes (iii) to (vi) have only alkyl chains and hence no oxygen atoms around the core. The metal atom used for coordination has been chosen as Cu/Pd/Ni. Determination of the crystal and molecular structures of these discogens has led to the identification of the following similarities: (1) All the six discogens crystallize in the triclinic space group P1. The recurrence of the space group may be correlated with the structural requirements for efficient packing of the molecules in the crystal lattice. (2) The coordination around the metal atom is square planar. (3) The 11 atom core is only nearly planar. (4) The phenyl rings and the chains are tilted with respect to the core. (5) The molecular conformation in the crystal confers a nearly rectangular shape to these discogens. (6) The chains are fully extended in an all trans conformation. (7) The molecular arrangement is tilted columnar except for the crystal structure of complex (ii).In addition to the similarities, distinct differences in the crystal structural characteristics have also been observed. For example, when oxygen atoms are present in the fringe, the molecules have no crystallographic symmetry and they tend to pair. In the crystal structure of (i) where the repeat unit along the column is a molecular pair, the metal atoms are distributed in a zig-zag fashion. In the other crystals with columnar arrangement, the metal atoms are stacked one over another. Complex (ii) has a layer-like molecular arrangement in the crystalline phase.