Synthesis, spectral characterization, and single crystal X-ray structures of a series of manganese-2,2′-bipyridine complexes derived from substituted aromatic carboxylic acids

Reaction of [Mn(2,2′-bpy)2(OAc)](ClO4)(H2O) with a series of aromatic carboxylic acids yields new Mn(II)carboxylates [Mn(2,2′-bpy)2(L)](ClO4)}2 (1–3), [Mn(2,2′-bpy)2(L)2] (4–5) and [Mn(2,2′-bpy)2(L)(H2O)](ClO4) (6) (L = 2-aminobenzoate (2-aba) (1), 4-hydroxybenzoate (4-hba) (2), thiophene-2-carboxylate (2-tca) (3), 2-hydroxynapthoate (2-hnapa) (4), 3,5-diisopropylsalicylic acid (dipsa) (5), 2,4,6-triisopropylbenzoate (tipba) (6)). The new compounds have been characterized with the aid of elemental analysis, spectroscopy, and single-crystal X-ray diffraction studies. Compounds 1–3, which have been synthesized from less bulky carboxylic acids, are dimeric in the solid-state. Compounds 4–6, which are derived from more bulkier aromaric carboxylic acids, exist as monomeric complexes. In the case of 6, where very bulky 2,4,6-triisopropyl benzoic acid is used as the starting material, only one carboxylate ligand binds to the metal, resulting in a cationic complex. Interestingly in all the six complexes, the C–H hydrogen atoms of the 2,2′-bpy ligands are involved in extensive hydrogen bonding with the carboxylate oxygen atoms of the adjacent molecules and hence form non-covalent 1-D or 2-D aggregates in the solid state.

Graphical abstractMono- and dinuclear Mn(II)-2,2’-bipyridine complexes containing aromatic carboxylic acid ligands bearing additional functional groups and bulky alkyl substituents exhibit interesting supramolecular association aided by hydrogen bonding and π-π stacking interaction.Figure optionsDownload full-size imageDownload as PowerPoint slide