COORDINATION GEOMETRIES AND COOPERATIVE ORDERING EFFECTS IN COPPER(II) COMPLEXES WITH TRIDENTATE SCHIFF-BASE DIANIONS .4. EPR MONOCRYSTAL INVESTIGATION OF -SALICYLIDENE-(R,S)-ALPHA-ALANINATO)]DICUPRATE(II)

Some aspects of the crystal structure of sium-bis[(mu-isocyanato-N,O){ N-salicylidene-(R,S)- alpha-alaninato}] dicuprate(II), K-2[Cu-2{sal-R, S-ala}(2)(mu-NCO)(2)], necessary for the interpretation of EPR monocry stal spectra are reported. The crystal structure consists of centrosym metric binuclear [Cu-2{sal-R,S-ala}(2)(mu-NCO)(2)](2-) complex anions connected with the K+ ions by electrostatic forces. The coordination a round Cu-II is approximately square-pyramidal. The basis of the pyrami d is formed by the donor atoms, O,N,O of the tridentate Schiff base li gand and the N atom of the additional NCO- ligand. Completion of the p yramid is achieved by a weak apical contact (Cu-O' = 2.70 Angstrom) to the terminal O atom of the NCO- ligand within the dimeric unit. The t wo dimeric anions in the unit cell ar mutally canted by an angle 2 gam ma=75.5 degrees. The EPR powder spectrum shows molecular g components g(x) = 2.043, g(y) = 2.055, g(z) = 2.232. In measurements on the monoc rystal two angular-dependent EPR lines, which are phase-shifted in the ab plane by the above canting angle 2 gamma, confirm the distributed antiferrodistortive arrangement of two separate chains (nearest Cu ... Cu spacings: 8.66 Angstrom) of ferrodistortively stacked Cu-II specie s.