Unusual cocrystals made of a Schiff base metal complex and an organic molecule - Close-packing vs. hydrogen bond interactions

The mononuclear complexes [ML2]0 (M = Co, Ni, Zn; HL - Schiff base ligand formed in situ from 2-pyridinecarbaldehyde and anthranilic acid, AA) can efficiently interact with unreacted AA molecules to produce CoL2·AA·H2O (1), NiL 2·AA·H2O (2) and ZnL 2·AA·0.25CH3OH·0.5H2O (3) cocrystals. Compounds 1-3 have been obtained as single crystals and characterized by elemental analysis, IR spectroscopy, thermal analysis, and single-crystal X-ray diffraction techniques. The compounds crystallize in the triclinic space group P1̄, with 1 and 2 being isomorphous. Neutral ML 2 molecules in 1-3 show no crystallographically imposed symmetry with the metal atoms octahedrally surrounded by two anionic ligands in a mer configuration. Of the two crystallographically distinct AA molecules, one molecule only is engaged in H-bonding N/OH⋯O interactions with ML 2 units. The solid-state organization of the cocrystals is described as an insertion of the organic molecules between the layers of ML2 complexes as they occur in the reported native NiL2·H 2O structure. © 2014 Elsevier B.V. All rights reserved.