Mn(II) coordination architectures with mixed ligands of 3-(2-pyridyl)pyrazole and carboxylic acids bearing different secondary coordination donors and pendant skeletons

In our efforts to investigate the factors that affect the formation of coordination architectures, such as secondary coordination donors and pendant skeletons of the carboxylic acid ligands, as well as H-bonding and other weak interactions, two kinds of ligands: (a) 3-(2-pyridyl)pyrazole (L1) with a non-coordinated N atom as a H-bonding donor, a 2,2′-bipyridyl-like chelating ligand, and (b) four carboxylic ligands with different secondary coordination donors and/or pendant skeletons, 1,4-benzenedicarboxylic acid (H2L2), 4-sulfobenzoic acid (H2L3), quinoline-4-carboxylic acid (HL4) and fumaric acid (H2L5), have been selected to react with Mn(II) salts, and five new complexes, [Mn(L1)2(SO4)]2 (1), [Mn(L1)2(L2)]∞ (2), [Mn(L1)(HL3)2]∞ (3), Mn(L1)2(L4)2 (4), and [Mn(L1)2(L5)]∞ (5), have been obtained and structurally characterized. The structural differences of 1–5 can be attributed to the introduction of the different carboxylic acid ligands (H2L2, H2L3, HL4, and H2L5) with different secondary coordination donors and pendant skeletons, respectively. This result also reveals that the typical H-bonding (i.e. N–H⋯O and O–H⋯O) and some other intra- or inter-molecular weak interactions, such as C–H⋯O weak H-bonding and π⋯π interactions, often play important roles in the formation of supramolecular aggregates, especially in the aspect of linking the multi-nuclear discrete subunits or low-dimensional entities into high-dimensional supramolecular networks.

Five new Mn(II) complexes with mixed ligands, 3-(2-pyridyl)pyrazole and carboxylic acids bearing different secondary coordination donors and pendant skeletons have been synthesized and structurally characterized. Their structures are different mainly due to the different secondary coordination donors and pendant skeletons of the carboxylic acid ligands. In addition, intra- or inter-molecular H-bonding and π⋯π interactions also play important roles in the formations of such complexes, and further link the discrete subunits or low-dimensional entities into high-dimensional supramolecular assemblies.Figure optionsDownload as PowerPoint slide