Framework Control by a Metalloligand Having Multicoordination Ability: New Synthetic Approach for Crystal Structures and Magnetic Properties

By utilizing the novel metalloligand LCu, [Cu(2,4-pydca)2]2- (2,4-pydca2- = pyridine-2,4-dicarboxylate), which possesses
two kinds of coordination groups, selective bond formation with the series of the first-period transition metal ions
(MnII, FeII, CoII, CuII, and ZnII) has been accomplished. Depending on the coordination mode of 4-carboxylate with
CoII, CuII, and ZnII ions, LCu 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}n (2), [ZnLCu(H2O)2(MeOH)2]n (3), and {[MLCu(H2O)4]·2H2O}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 CuII ion, gives
a zigzag 1-D assembly with the similar repeating unit as 4−6:  {[Cu(2,2‘-bpy)LCu]·3H2O}n (9). On the other hand,
for MnII and FeII ions, LCu 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 LCu 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 (CuII−MII; MII = MnII, J/kB = 0.69 K for 7; MII
= FeII, J/kB = 0.71 K for 8).