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), NiL2·AA·H2O (2) and ZnL2·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 P 1 ‾ , with 1 and 2 being isomorphous. Neutral ML2 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 ML2 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·H2O structure.