Four coordination polymers based on dinuclear and trinuclear units with a new multifunctional pyridyl-dicarboxylate ligand: luminescence and magnetic properties

Abstract

Four coordination polymers of different transition metal ions with a new pyridyl-dicarboxylate ligand, 4-(3,5-dicarboxylphenyl)-2-methylpyridine (H₂L), were synthesized under solvothermal conditions and their structures and properties were characterized. They are formulated as [Zn(L)(H₂O)]·H₂O (1), [Mn₃(L)₂Cl₂(H₂O)₂]·2H₂O (2), [Co₃(L)₂(NO₃)₂(H₂O)₂] (3) and [Ni₃(L)₂(NO₃)₂(H₂O)₂]] (4). Compound 1 exhibits a 2D network with a (3,6)-connected kgd topology based on the dinuclear [Zn₂O₂] units. In compound 2, the linear trinuclear [Mn₃(μ-O_carboxylate)₂(COO)₂Cl₂] units with mixed carboxylate and μ-Cl triple bridges are cross-linked by the L ligands into a 3D framework with a (3,6)-connected rtl topology. Compounds 3 and 4 are isostructural and both show 2D networks in which the linear trinuclear [M₃(μ-O_carboxylate)₂(COO)₂(μ-O_NO3)₂] units (M = Co (3) and Ni (4)) are cross-linked by the L ligands. Compound 1 shows strong blue emissions in the solid state at room temperature. Magnetic studies indicate that the mixed triple [(μ-O_carboxylate)(COO)Cl] bridges transmit antiferromagnetic interactions between Mn(II) ions in 2, while the mixed triple (μ-O_carboxylate)(COO)(μ-O_NO3) bridges in 3 and 4 transmit ferromagnetic interactions. Further magnetic studies demonstrated that the Co(II) compound shows no long-range magnetic ordering at 2 K.