Cobalt(III) complexes containing incomplete C3O4 or complete Co4O4 cubane core

The modeling study of the photosynthetic water oxidation center has been extended to the cobalt(III) complexes with incomplete or complete cubane core. In the preparation of the [Co-3(N-N-O)(3)(mu-OH)(3)(mu(3)-O)](+) complexes from [Co(N-N-O)(H2O)(3)](2+), some isomers of the trinuclear complexes with three N-H...O hydrogen bonds are stereoselectively formed, as shown in the following: in the 38 possible geometrical isomers of [Co-3(edma)(3)(mu-OH)(3)(mu(3)-O)](+) (edma: ethylenediamine-N-acetato(1-)), each of the isolated four isomers has the three N-H...O hydrogen bonds, which was isolated. The tetranuclear cobalt(III) complex with Co4O4 core was not isolated when using edma as ligand, but isolated when using pg (pg = 2-pyridylmethylglycinato(1-)); the X-ray data shows that the Co4O4 structure of [Co-4(pg)(4)(mu(3)-O)(4)] was stabilized by four N-H...O hydrogen bonds and two pairs of pyridyl-pyridyl attractive interactions. In the trinuclear L-histidinato complex, only one isomer has three hydrogen bonds, which was isolated. However, using D,L-histidine instead of L-histidine, the major products isolated were dinuclear cobalt(III) complexes. (C) 2000 Elsevier Science S.A. All rights reserved.