METAL ION-INDUCED SELF-ASSEMBLY OF OPEN-CHAIN TETRAPYRROLE DERIVATIVES - DOUBLE-STRANDED DINUCLEAR COMPLEXES FROM 10-OXO-5,15-BILADIENES

Syntheses of double stranded neutral species via the complexation of Z n, Cd, and Hg with 10-oxo-5,15-biladiene LH2 are described. Formation of the single stranded Cd complex indicates that the self assembly pro cess which affords the double stranded system is not simply a conseque nce of relief of steric strain. The crystal structure of the cadmium(I I) double stranded dimer 8 is described. Long contact distances betwee n carbonyl spacers and Cd ions in the crystal structure of 8 complete the coordination sphere of each Cd, concomitantly forming two distorte d trigonal bipyramidal metal centers. Fast coordination/decoordination phenomena involving the carbonyl spacers and the two metallic centers in the zinc(II), cadmium(II) and mercury(II) dimeric complexes 7, 8 a nd 9, respectively, are investigated by using variable temperature H-1 NMR. A bending/twisting process is proposed, and its associated energ y barrier (40-50 kJ mol(-1)) is determined for the first time. (C) 199 8 Elsevier Science Ltd. All rights reserved.