Single hydroxy bridges have been shown to mediate strong antiferromagnetic exchange between copper (I1) centres, depending on the oxygen bridge angle and the ground state of the metal ion (1-4) and in some cases very large exchange integrals are observed (-25> 800 cm-')(2, 3) approaching the range observed for binuclear copper protein centres (5, 6); For dihydroxy bridged systems exchange integrals are somewhat smaller, with a linear ...