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

• Cocrystals of Schiff base Co, Ni and Zn complexes and anthranilic acid were reported.
• The organic molecules are inserted between the layers of ML2 units.
• The two independent AA molecules in 1–3 show different H-bonding preferences.
• The solid-state architectures of 1–3 and a parent complex are contrasted.
• Thermal behaviour of 1 and 3 was investigated.

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 P1‾, 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.

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