Synthesis and Characterization of a Tetracopper(II) Complex Having a [Cu4(µ4-O)] Framework Stabilized by the Tetranucleating Macrocyclic Ligand

A tetranucleating macrocyclic ligand bearing four acetate pendants, L6−, was newly yielded by a stepwise synthesis from [Zn4(L′)(AcO)2(OH)2](ClO4)2·H2O (1), which was prepared from [2 + 2] Schiff-base condensation of 2,6-diformyl-4-methylphenol and 1,2-bis(2-aminoethoxy)ethane in the presence of Zn(ClO4)2·6H2O, sodium acetate, and triethylamine. A µ4-oxo tetracopper(II) complex [Cu4(L)(µ4-O)]·H2O (2) was obtained from the reaction of Cu(ClO4)2·6H2O and Na2H4L in methanol under basic conditions, and characterized by X-ray crystallography. Two adjacent copper centers were bridged by the phenoxo oxygen of L6− to form [Cu2(µ-OPh)] unit, two pairs of which were further linked by an oxo anion with a distorted tetrahedral geometry, finally creating a tetracopper core [{Cu2(µ-OPh)}2(µ4-O)]. Cryomagnetic measurements of 2 in the range of 2–300 K exhibited antiferromagentic behavior. Magnetic analysis of 2 was carried out by the four spin-exchange interactions model based on the bridging mode and the Cu–(µ4-O)–Cu angles, JA: Cu1/Cu4, JB: Cu2/Cu3, JC: Cu1/Cu2 and Cu3/Cu4, and JD: Cu1/Cu3 and Cu2/Cu4 pairs. The estimated four magnetic exchange interactions (JA, JB, JC, and JD) were −17, −161, −108, and −109 cm−1, respectively.