Three-dimensional manganese(II) coordination polymers based on m-pyridinecarboxylates: synthesis, X-ray structures, and magnetic properties.

Strong metal-ligand coordination bonds and their directionality have recently been extensively exploited for the design and synthesis of extended solid materials.1-7 Compared to metal oxides and other simple inorganic solids, the structural diversity of polymeric coordination networks can be enormous owing to the ability to incorporate a vast number of organic ligands into the frameworks. The prospect of tuning the properties of metalorganic frameworks via a systematic change of the organic linking ligands provides further impetus for the research on metal-organic frameworks.8-11 Our recent preliminary results on the tuning of nonlinear optical properties of coordination networks by incorporating organic linking ligands of different length (hence conjugation) illustrate the potential of such a rational synthetic approach.12-14 However, due to the presence of many subtle interactions in such supramolecular systems, the construction of extended solids based on metal-organic coordination networks is still at a primitive stage and lacks predictability.15 The detailed knowledge of such interactions on metal-organic coordination networks can be obtained by systematically changing the organic bridging ligands (building blocks). Our work focuses on the construction of coordination networks by using bridging ligands with the same geometry but different length, in particular conjugated π-systems.12-14,16 Such ligands have rigid conformations and will therefore simplify the crystal engineering of the resulting coordination networks. Herein we wish to report the synthesis, X-ray structures, and magnetic properties of two topologically similar 3-D manganese(II) coordination polymers based on bridging m-pyridinecarboxylate: bis(nicotinato)manganese and bis[4-(3pyridyl)ethynylbenzoato]manganese.