Synthesis and crystal structure of a first-generation model for the trinuclear copper site in ascorbate oxidase and of a dinuclear silver precursor

Abstract

The synthesis and X-ray crystal structure of a disilver complex [Ag₂L¹][BF₄]₂ of a bibracchial tetraimine Schiff-base macrocycle derived from the silver-templated cyclocondensation of 2,6-diacetylpyridine and tris(2-aminoethyl)amine are reported. The complex crystallises in the monoclinic space group P2₁/n(a non-standard setting of P2₁/c, no. 14) and has unit-cell dimensions a= 11.660(22), b= 28.14(4), c= 12.158(21)Å, β= 107.94(13)° with Z= 4. Functionalisation of the pendant arms with salicylaldehyde followed by transmetallation with Cu^II leads to the formation of a trinuclear copper(II) complex [Cu₃L⁴-(OH)][ClO₄]₃·2H₂O in which there is a single Cu^II atom 4.9 and 5.9 Å distant from a pair of Cu^II atoms which are 3.6 Å apart and hydroxy-bridged. The complex, which crystallises in the monoclinic space group P2₁(no. 4) and has unit cell dimensions a= 13.997(24), b= 16.043(9), c= 14.353(11)Å, β= 118.97(10)° with Z= 2, may be regarded as a first-generation model for ascorbate oxidase. A study of the magnetic properties shows that the trinuclear copper(II) complex can be regarded as a mononuclear site non-interacting with a moderately coupled copper pair (2J=–202 cm^–1).