STRUCTURE AND CONFORMATION OF PHOTOSYNTHETIC PIGMENTS AND RELATED-COMPOUNDS .6. THE 1ST CRYSTAL-STRUCTURE OF A COVALENTLY-LINKED CHLORIN DIMER - 20,20'-ETHYLENEBIS(TRANS-2,3,7,8,12,13,17,18-OCTAETHYLCHLORIN)

The crystal structure of the title compound 1 has been determined by X-ray diffraction methods to obtain structural information on covalently-linked chlorin dimers as biomimetic models for the photosynthetic reaction centre. The dimer crystallizes in two different crystal forms. Both forms show different macrocycle conformations which indicates the conformational flexibility of the chlorin macrocycle. This shows that not only the overall structural similarity but also conformational parameters have to be considered in the design of reaction centre models. Crystal data: Form angstrom: C74H98N8.CH2Cl2, monoclinic, space group C2/c with a = 32.610(9) angstrom, b = 10.804(2) angstrom, c = 21.185(5) angstrom, beta = 108.90(6)-degrees, and V = 7063(3) angstrom3, Z = 4. R = 0.073 (120 K). Form B: C74H98N8, monoclinic, space group C2/c with a = 24.068(14) angstrom, b = 10.216(6) angstrom, c = 26.44(3) angstrom, beta = 92.19(6)-degrees, V = 6497(7) angstrom3, Z = 4. R = 0.063 (130 K).