SYNTHESIS AND CRYSTAL-STRUCTURE OF A 1ST-GENERATION MODEL FOR THE TRINUCLEAR COPPER SITE IN ASCORBATE OXIDASE AND OF A DINUCLEAR SILVER PRECURSOR

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 P2(1)/n (a non-standard setting of P2(1)/c, no. 14) and has unit-cell dimensions a = 11.660(22), b = 28.14(4), c = 12.1 58(21) angstrom, beta = 107.94(13)-degrees 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 angstrom distant from a pair of Cu(II) atoms which are 3.6 angstrom apart and hydroxy-bridged. The complex, which crystallises in the monoclinic space group P2,(no. 4) and has unit cell dimensions a = 13.997(24), b = 16.043(9), c = 14.353(11) angstrom, beta = 118.97(10)-degrees 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).