A series of tetranuclear [2 × 2] grid complexes derived from an asymmetric ligand: Structural differences based on metal ion affinities*

A series of tetranuclear grid-type complexes were prepared by the reaction of the asymmetric multidentate ligand HL (HL = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridine carboxylic acid ethylester) with different metal sources. The tetranuclear copper complex, [Cu4(L1)4(NO3)4(H2O)4] Et2O 2MeOH (1, HL1 = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridine carboxylic acid methyl ester) consists of four ligands, four copper ions, four nitrate ions and four water molecules, forming a [2 × 2] grid structure, in which all four copper ions have the same coordination environment. On the other hand, the corresponding nickel and cobalt complexes, [M4(L2)4(H2O)4] 4MeOH 6H2O (M = Ni (2) and Co (3), (H2L2 = 6-[1,3-dioxo-3-(2-phenyl)propionyl]pyridine-2-carboxylic acid)), have a similar grid core structure to the copper complex with four metal ions, four ligand molecules, and four water molecules, however, in these clusters there are two kinds of coordination site for the metal ions. Temperature-dependent magnetic susceptibility measurements for all complexes demonstrated that antiferromagnetic interactions between the metal ions were in operation. The magnetic susceptibility data of the copper and nickel complexes were analyzed using a tetranuclear model based on H = –2J(S1S2+S2S3+S3S4+S4S1) to give best-fit parameters of g = 2.11(1), J = –1.39(3) cm–1 and g = 2.19(1), J = –0.44(2) cm–1, respectively.