SPIN-DENSITY IN AN ENAMINOCETONE NITROXIDE COPPER COMPLEX

The copper complex C(18)H(28)O(2)N(2)Cn(NO)(2) is a molecule which car ries three spins S=1/2. It crystallizes in the monoclinic space group Pc, with two molecules in the asymetric unit. Its chi T starts to incr ease when the temperatures decreases, indicating ferromagnetic intramo lecular coupling, and then, below T=40K, it completely collapses, show ing negative coupling between molecules. We have investigated its spin density with polarized neutrons at T=40K and T=4.10K. At the higher t emperature, the spin density is well localized on the Cu atom and the two NO groups of each molecule. At the lower temperature, the spin den sity exists, for each molecule, on the Cu atom and on one of the two N O groups only. There is a quasi dimerization on two NO groups, belongi ng to the different molecules, facing each other, and distant only by 3.40 Angstrom.