Framework control by a metalloligand having multicoordination ability: New synthetic approach for crystal structures and magnetic properties

By utilizing the novel metalloligand L-Cu [Cu(2,4-pydca)(2)](2-) (2,4-pydca (2-) = pyridine-2,4-dicarboxylate), which possesses two kinds of coordination groups, selective bond formation with the series of the first-period transition metal ions (Mn-II, Fe-II, Co-II, Cu-II, and Zn-II) has been accomplished. Depending on the coordination mode of 4-carboxylate with Co-II, Cu-II, and Zn-II ions, L-Cu forms a one-dimensional (1-D) assembly with a repeating motif of [-M-O2C-(py)N-Cu-N(py)-CO2-]: {[ZnLCu(H2O)(3)(DMF)](DMF)-D-.}(n) (2), [ZnLCu(H2O)(2)(MeOH)(2)](n) (3), and {[MLCu(H2O)(4)](.)2H(2)O}(n) (M = Co (4), Cu (5), Zn (6)). The use of a terminal ligand of 2,2'-bipyridine (2,2'-bpy), in addition to the Cu-II ion, gives a zigzag 1-D assembly with the similar repeating unit as 4-6: {[Cu(2,2'-bpy)L-Cu](.)3H(2)O}(n) (9). On the other hand, for Mn-II and Fe-II ions, L-Cu shows a 2-carboxylate bridging mode to form an another 1-D assembly with a repeating motif of [-M-O-C-O-Cu-O-C-O-]: [MLCu(H2O)(4)](n) (M = Mn (7), Fe (8)). This selectivity is related to the strength of Lewis basicity and the electrostatic effect of L-Cu and the Irving-Williams order on the present metal ions. According to their bridging modes, a variety of magnetic properties are obtained: 4, 5, and 9, which have the 4-carboxypyridinate bridge between magnetic centers, have weak antiferromagnetic interaction, whereas 7 and 8 with the carboxylate bridge between magnetic centers reveal 1-D ferromagnetic behavior (Cu-II-M-II; M-II = Mn-II, J/k(B) = 0.69 K for 7; M-II = Fe-II, J/k(B) = 0.71 K for 8).