Temperature-controlled synthesis of two novel coordination polymers modeled by semi-rigid tetrapyridines

Abstract

Solvothermal reactions of tetrakis(4-pyridyloxymethylene)methane (TPOM) with deprotonated benzoate (L1) in the presence of acetate (L2) of copper in H₂O/CH₃OH with reactant ratio 1 : 2 : 2 under different synthesis temperatures produced two new complexes, namely, {[Cu₂(TPOM)₂(L1)₂(L2)₂]·Guest}_n (1), and {[Cu₄(TPOM)(L1)₂(L2)₄(OH)₂]·6H₂O}_n (2). These complexes were characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. Complex 1 reveals a 3D crystal structure with a novel 2,3,4-connected 3-nodal topology constructed from the connection of Cu centers and TPOM ligands, which neutralized the mono-dentate carboxylates from different ligands coordinated to Cu ions. Complex 2 exhibits a distinct 3D framework with 2-nodal PtS topology, constructed from the connection of neutral Cu₄ SBUs and TPOM ligands. The increasing reaction temperature must be responsible for the versatile coordination modes of carboxylates in 2 compared to the ones in 1, resulting in the formation of the distinct crystal structure. In addition, magnetic investigations on complex 2 revealed antiferromagnetic intra-tetramer interactions through the mixed hydroxo and carboxylato bridges.